Unlocking the Kimberley's Past: the Applicability of Organic Spring

Unlocking the Kimberley’s past: The applicability of organic spring deposits for reconstructing late Quaternary climatic and environmental change

Emily Field

M.Sc. Quaternary Science, 2010

B.A. (Hons) Geography, 2009

A thesis submitted for the degree of Doctor of Philosophy at

The University of Queensland in 2018

School of Earth and Environmental Sciences

Abstract

There are limited high-resolution records of climatic and environmental change from the Kimberley region of northwest Australia. This has hindered the development of knowledge of climate and environmental change in Australia’s monsoonal tropics, and the ability to provide context for the area’s rich archaeological record and globally renowned rock art. The lack of high-resolution records from this region is primarily a result of the monsoonal climate which limits the presence of “classic” palaeoenvironmental archives such as perennial lakes and wetlands. Organic spring deposits are unconventional archives of past environmental change yet offer potential to provide outstanding records in arid and semi-arid regions such as the Kimberley. Despite this, the majority of existing research demonstrates complications with their use, in particular the application of standard radiocarbon (14C) techniques to build robust chronologies of their development. Because of the importance of springs as critical palaeoenvironmental archives, and the pressing need for high-resolution records from northwest Australia, this thesis utilised three organic spring deposits to develop new, high-resolution records of climate and environmental change for the Kimberley. These records span the last ~14,500 years, and were underpinned by a new protocol for establishing robust chronologies from these settings which was developed via a rigorous geochronological investigation.

Initial 14C results from a core collected from Black Springs in 2005 were confusing, with convoluted ages below 94.5 cm limiting the reliability of an initial palaeoenvironmental reconstruction >9070 cal. yr BP. A new protocol for obtaining robust chronologies from organic spring deposits was therefore developed for cores collected from the three sites in 2015, utilising multiple geochronological methodologies including 14C dating of different carbon fractions (stable polycyclic aromatic carbon (SPAC), macro-charcoal, pollen concentrate, bulk sediment and roots), 210Pb dating, the application of 239+240Pu, and high-spatial resolution, luminescence techniques

(natural sensitivity-corrected luminescence (Ln/Tn)). Whilst Ln/Tn demonstrated that the organic spring deposits contained a relatively uncompromised stratigraphic record, 14C dates were contaminated by roots, groundwater fluctuations, and incorporation of allochthonous “old” carbon. SPAC isolated by the hydrogen pyrolysis (HyPy) pre-treatment appeared to remove post- depositional sources of alteration, and therefore provided a viable approach for constructing chronologies in these settings. Developing more recent chronologies (i.e. the past 100 years) using 210Pb was found to be problematic due to the behaviour of the springs as an open system with regards to uranium, suggesting this may not be possible in many spring environments. Whilst this investigation was made with respect to springs, the contamination pathways are not unique to these

settings and therefore the chronological developments are more widely applicable (e.g. for constructing chronologies in archives subject to deep root growth and/or significant changes in hydrology).

This new dating protocol enabled the climatic and environmental reconstructions from the three new records presented in this thesis to be placed on secure timescales. These new records utilised pollen, micro-charcoal, non-pollen palynomorphs (NPPs) and elemental geochemistry (Itrax micro X-ray fluorescence (µXRF) core scanning). Principal Components Analysis (PCA) axis 1 scores demonstrated similarity between inter-site elemental geochemistry and non-pollen palynomorph datasets, although there were significant discrepancies between the pollen records which reflected predominantly local conditions. In order to isolate dominant modes of regional variability, Monte Carlo Empirical Orthogonal Function (MCEOF) analysis was applied to proxies from the geochemistry and NPP datasets, providing a regional reconstruction of climatic variability in the Kimberley for the last 14,500 years. The results of this reconstruction show increasing monsoon activity from 14,500 cal. yr BP consistent with the deglaciation, followed by peak monsoon activity during the early-Holocene (between ~11,000 – 7500 cal. yr BP). There is a trend of decreasing monsoon activity throughout the remainder of the Holocene, interrupted by a short period of wetter conditions at ~4200 cal. yr BP, and peak aridity spanning ~2600 – 1000 cal. yr BP.

This thesis makes a significant contribution to understanding of climatic change in Australia’s monsoonal tropics, in particular long-term changes in monsoon activity in northwest Australia since the Last Glacial-Interglacial Transition (LGIT). It also provides a method for building reliable chronologies in organic spring deposits which are critical palaeoenvironmental archives in arid and semi-arid environments. In light of the Kimberley’s rich archaeological record, requirements have been highlighted for the need to extend high-resolution palaeoclimate reconstructions in the region to ~50,000 cal. yr BP to encompass the entire known history of likely human occupation in the region.

Declaration by author

This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis.

I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my higher degree by research candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award.

I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School.

I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co-authors for any jointly authored works included in the thesis.

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Publications during candidature

Peer reviewed papers:

Field, E., McGowan, H., Moss, P., Marx, S., 2017. A late Quaternary record of monsoon variability in the northwest Kimberley, Australia. Quaternary International 449, 119 – 135.

Field, E., Marx, S., Haig, J., May, J.-H., Jacobsen, G., Zawadzki, A., Child, D., Heijnis, H., Hotchkis, M., McGowan, H., Moss, P., 2018. Untangling geochronological complexity in organic spring deposits using multiple dating methods. Quaternary Geochronology 43, 50 – 71.

Conference abstracts:

Child, D., Hotchkis, M., Marx, S., Knight, J., Field, E., 2017. The Australian fallout isotopic signature – implications for sediment fallout chronometry. The 14th International Conference on Accelerator Mass Spectrometry, P31, Ottawa, Canada.

Field, E., Haig, J., May, J.-H., Marx, S., Jacobsen, H., Zawadski, A., Child, D., Heijnis, H., McGowan, H., Moss, P., 2016. Using multiple dating methods to understand controls on geochronological complexity in organic spring deposits. AQUA Biennial Meeting, P58, Auckland, New Zealand.

Field, E., Moss, P.T., McGowan, H.A., Gadd, P., 2016. Evidence of regionally synchronous environmental and climatic change across the Kimberley during the Holocene. AQUA Biennial Meeting, P59, Auckland, New Zealand.

Field, E., Moss, P.T., McGowan, H.A., 2016. A late Quaternary fire history of the Kimberley region, northwest Australia: New records from the Northern Kimberley Bioregion. Bushfire Conference, P80-02, Brisbane, Australia.

Field, E, McGowan, H.A., Jacobsen, G., Heijnis, H., Zawadzki, A., Child, D., Haig, J., Marx, S., Moss, P.T., 2016. Gaining new high-resolution palaeoclimate information from Australia’s water-limited environments: Dating the “un-dateable” of cores. AESC Conference, P52, Adelaide, Australia.

Field, E., McGowan, H.A., Moss, P.T., Marx, S., Hammond, A., 2015. Using established approaches in a challenging new environment: The first palaeo-environmental records from mound springs in the Kimberley region of north Western Australia. INQUA Congress, P89, Nagoya, Japan.

Field, E.; McGowan, H.A., Moss, P.T., Marx, S., Hammond, A., 2015. New records and approaches for past climate reconstruction in the Kimberley region of northwest Australia. AMOS Conference, Brisbane, Australia.

Publications included in this thesis

Field, E., McGowan, H., Moss, P., Marx, S., 2017. A late Quaternary record of monsoon variability in the northwest Kimberley, Australia. Quaternary International 449, 119 – 135. Incorporated as Chapter 5.

Contributor Statement of contribution Emily Field (Candidate) Conception and design (100%) Analyses and interpretation (70%) Drafting and production (70%) Hamish McGowan Analyses and interpretation (10%) Drafting and production (10%) Patrick Moss Analyses and interpretation (10%) Drafting and production (10%) Sam Marx Analyses and interpretation (10%) Drafting and production (10%)

Contributor Statement of contribution Emily Field (Candidate) Conception and design (80%) Analyses and interpretation (60%) Drafting and production (60%) Sam Marx Conception and design (20%) Analyses and interpretation (10%) Drafting and production (5%) Jordahna Haig Analyses and interpretation (10%) Drafting and production (5%) Jan-Hendrik May Analyses and interpretation (5%) Drafting and production (5%) Geraldine Jacobsen Analyses and interpretation (5%) Drafting and production (2.5%) Atun Zawadzki Analyses and interpretation (5%)

Drafting and production (2.5%) David Child Analyses and interpretation (5%) Drafting and production (2.5%) Henk Heijnis Drafting and production (5%) Michael Hotchkis Drafting and production (2.5%) Hamish McGowan Drafting and production (5%) Patrick Moss Drafting and production (5%)

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Contributions by others to the thesis

Standard contributions were made by the supervisory team of Professor Hamish McGowan and Associate Professor Patrick Moss. This included shared project design, assistance with technical support, and revisions and editing of this thesis. Pauline Heaney of the Takarakka Nowan Kas Rock Art Archive produced Figure 4.4, Figure 4.7, Figure 4.9 and Figure 4.10. Dr Andrew Hammond and the late Dr Grahame Walsh were responsible for the collection of core BSP00 from Black Springs presented in Chapter 5, whilst Hamish McGowan, Patrick Moss, Sam Marx and Andrew Hammond coordinated the majority of radiocarbon dating of core BSP00 (Field et al., 2017; Field et al., 2018). Dr Lydia Mackenzie assisted in laboratory work on the cores collected in 2015, including core sub- sampling and loss-on-ignition (LOI). Dr Jordahna Haig ran radiocarbon (14C) samples through the hydrogen pyrolysis (HyPy) rig at James Cook University, whilst natural sensitivity-corrected luminescence (Ln/Tn) analysis was undertaken at The University of Freiburg, the results of these analyses being presented in Chapter 6. Dr Sam Marx also produced Figure 6.7 - Figure 6.10, Figure 6.12Figure 6.13 within this Chapter. Dr Jon Tyler assisted with statistical analysis, and produced Figure 7.10 - Figure 7.13 presented in Chapter 7.

Statement of parts of the thesis submitted to qualify for the award of another degree

None

Research Involving Human or Animal Subjects

No animal or human participants were involved in this research

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Acknowledgements

There is a small army of people to thank throughout the course of my PhD candidature! Firstly I would like to thank my advisory team who have been fantastic supervisors throughout. I am extremely grateful to my principal supervisor, Hamish McGowan, for the opportunity to undertake this PhD and for his continued guidance and much valued critique of my work. Hamish has been a mentor and friend since I commenced this project in 2014, and has provided me with the opportunity to travel around Australia to workshops and on fieldwork both in relation to my own research, and to help on other projects. I am very grateful to have had his help and sense of humour in the 2015 field campaign, including his ability to keep a cool head in the event of a colleague becoming “lost” in the outback! I am sincerely thankful for his continued support, particularly for employing me as a research assistant and tutor, and especially for his career advice and for acting as a referee which enabled me to organise employment post-PhD.

I would also like to thank my co-supervisor, Patrick Moss, in particular for his input and training in the lab with regards to pollen analysis and processing. Patrick entrusted me with not only tutoring but also supervision of summer students, for which experience I am very grateful. I am deeply appreciative of his support of my attendance on field trips and at workshops, in particular his support for my attendance at a Tilia Workshop at the Australian National University, without with I would not have developed some of the skills so essential for completing this PhD.

I would like to extend my gratitude to Sam Marx, without whom many of my ideas would still be floundering and much of my writing would not have the finesse it needed. Thank you for your company during the 2015 field campaign to the Kimberley, for invitations to visit Wollongong, and for the opportunities to collaborate.

This PhD would not have been possible without the unwavering and generous support of the Kimberley Foundation Australia. I would like to thank the Foundation for their financial support which enabled me to complete this research and attend their Science Advisory Council annual workshops. These workshops enabled me to meet a cohort of other researchers and I have constantly been amazed at the brilliant interdisciplinary nature of the work that the Foundation fosters. It was through these workshops that I was able to meet Pauline Heaney, who warmly invited me into her home to teach me about the wonderful rock art of the Kimberley, and who produced some beautiful graphics for this thesis (and also baked some delicious treats for me to enjoy during the rock art lessons).

Thank you to the Koeyers family of Drysdale River Station and the Lacey family of Mount Elizabeth Station in Western Australia, who provided excellent local knowledge and warm Kimberley hospitality during the 2015 field campaign. I would also like to extend my thanks to Andrew Hammond and the late Grahame Walsh who collected the original core (BSP00) from Black Springs in 2005. Without the donation of this core to UQ and the subsequent pilot study that was done on it, my PhD would never have come to life.

Thank you to Jamie Shulmeister and his lovely wife Val for their hospitality and invitations to numerous BBQs at their house. I would also like to extend my thanks to Jamie for unofficially taking on the role of my “career advisor”, and for providing guidance, references and support throughout my job hunt. I would also like to thank Jamie for entrusting me with designing new course content for GEOS1100 which was a rewarding experience.

I would also like thank Jon Tyler for his statistical expertise and readiness to collaborate following an idea born at the AQUA biennial meeting in Auckland, 2016. Thank you for giving up your time to work with me in Adelaide and for your subsequent assistance. I am also indebted to Michael Bird for his advice regarding my radiocarbon dating issues. Without his suggestions and introduction to Jordahna Haig the chronology for much of this work would be highly unreliable.

This research was partly funded by an AINSE Postgraduate Research Award. I would like to extend a big thank you to all those at ANSTO and AINSE who taught me new laboratory techniques and made the many weeks at Lucas Heights so enjoyable. The work I undertook at ANSTO enabled a large portion of this thesis to come to fruition, in particular the dating aspects presented in Chapter 6. Special thanks to Patricia Gadd, Henk Heijnis, Atun Zawadzki, Geraldine Jacobsen, David Child, Fiona Bertuch, Brodie Cutmore, Daniela Fierro, Jack Goralewski (and everyone else in Building 34) for the excellent company and training.

I would also like to recognise the wonderful SEES professional staff. Firstly to the brilliant HR and finance girls – Lia Whalley, Genna McNicol, Suhan Chin and Christina Jack- thank you for the hilarious conversations and your patience with my ineptitude at putting in timesheets correctly/lodging travel requests. I would also like to acknowledge the technical staff, including Linda Nothdurft, Michael Tobe, Eros Romero Bonilla, Bryn Base, Clwedd Burns, Alan Victor and Jurgen Overheu. Without them I would never have been able to access any field work equipment, freight it to a remote cattle station and back, deal with my IT issues, and work in the labs. In particular I would like to thank Linda who not only has been of fantastic assistance in the lab throughout my candidature, but has also become a cherished friend.

I would also like to thank all the friends I have made during my candidature who continued to make lab work, conference and workshop attendance, and my thesis write up enjoyable: Lydia Mackenzie, Dan Ellerton, Michael Gray, James Daley, Len Martin, Loraine Watson-Fox, Haidee Cadd, Helen Green, Fiona McRobie, Sarah Kachovich, William Goulding, Laura Phillips, Astrid Hentschel, Valeria Bianchi, Matthius Klawitter, Davide Pistellato, Djalmbu Hilder, Lincoln Steinberger and Joshua Soderhom just to name just a few. In particular, thanks to those who endured some less-than-ideal conference accommodation with me in Adelaide and Auckland, your humour made the hideous dorm rooms without windows in unsavoury locations bearable. I would like to extend a special thank you to Lydia, who provided additional support with some of my lab work, and who has been a constant source of PhD companionship whilst both near and afar.

Last, but my no means least, I would like to thank my family who have been incredibly supportive of my decision to undertake a PhD and have always shown an interest in my work. Most importantly I would like to thank my wonderful husband, Gavin, who has been there to share the entire journey with me. Thank you for comforting me when things seemed almost impossible, for listening to my frustrations, for championing me, and for pretending to be interested when I wanted to talk about my research! Thank you for encouraging me to pursue my dreams of achieving my PhD – without you it would not have been possible. Finally a big thank you to my daughter, whose imminent arrival into the world acted as a fantastic motivational tool to get this thesis finished!

Financial support

This research was completed whilst the candidate was the recipient of an Australian Postgraduate Research Award. The research was also supported by the Kimberley Foundation Australia, who provided a top-up scholarship, funding for laboratory and field work, and covered costs for annual interstate workshop attendance. This thesis was also supported by an AINSE Postgraduate Research Award (PGRA No. 2158493). I acknowledge the financial support from the Australian Government for the Centre for Accelerator Science at ANSTO through the National Collaborative Research Infrastructure Strategy (NCRIS).

Financial support was also provided by AINSE and the Australasian Quaternary Association (AQUA) to attend the AQUA Biennial Meeting in Auckland, 2016.

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Keywords

Kimberley, monsoon, organic springs, chronology, radiocarbon, palaeoclimate, palaeoenvironments

Australian and New Zealand Standard Research Classifications (ANZSRC)

ANZSRC code: 040606, Quaternary Environments, 40%

ANZSRC code: 040605, Palaeoclimatology, 30%

ANZSRC code: 040303, Geochronology, 30%

Fields of Research (FoR) Classification

FoR code: 0406, Physical Geography and Environmental Geoscience, 70%

FoR code: 0403, Geology, 30%

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Table of Contents

Unlocking the Kimberley’s past: The applicability of organic spring deposits for reconstructing late Quaternary climatic and environmental change ...... i Abstract ...... i Declaration by author ...... iii Publications during candidature ...... iv Publications included in this thesis ...... vi Contributions by others to the thesis ...... viii Statement of parts of the thesis submitted to qualify for the award of another degree ...... viii Research Involving Human or Animal Subjects ...... viii Acknowledgements ...... ix Financial support ...... xii Keywords ...... xiii Australian and New Zealand Standard Research Classifications (ANZSRC) ...... xiii Fields of Research (FoR) Classification ...... xiii Table of Contents ...... xiv List of Figures ...... xx List of Tables ...... xxix List of Equations ...... xxx List of abbreviations used in the thesis ...... xxxi 1 Introduction ...... 1

1.1 Introduction to thesis ...... 1

1.1.1 Context of this research...... 1

1.2 Archives of late Quaternary environmental and climatic change in the Kimberley ...... 2

1.2.1 Organic spring deposits ...... 3

1.3 Thesis resolution...... 4

1.3.1 Problem statement ...... 4 1.3.2 Aims and objectives ...... 5

1.4 Generalised research approach ...... 6 1.5 Thesis structure...... 7

2 Regional setting ...... 10

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2.1 Introduction and geographical setting ...... 10 2.2 The Kimberley’s geology, geomorphology and hydrogeology ...... 11 2.3 Vegetation ...... 12 2.4 Climate ...... 14 2.5 Characteristics of the study sites ...... 18

2.5.1 Black Springs ...... 19 2.5.2 Fern Pool ...... 21 2.5.3 Gap Springs ...... 22

2.6 Conclusion ...... 24

3 Assessing current knowledge of late Quaternary climate and environmental change in the Kimberley: a synthesis of available records ...... 25

3.1 Introduction ...... 25 3.2 Data analysis and interpretation ...... 25 3.3 Marine records ...... 29

3.3.1 Sediment cores ...... 29 3.3.2 Geomorphology ...... 34 3.3.3 Corals ...... 34

3.4 Terrestrial records...... 35

3.4.1 Sediment cores ...... 35 3.4.2 Speleothems ...... 37 3.4.3 Geomorphology ...... 39 3.4.4 Archaeological sites ...... 41

3.5 Synthesis of climatic and environmental change in the Kimberley ...... 43 3.6 Conclusion: gaps in the current state of knowledge and future research ...... 48

4 The Kimberley’s human history: evidence of human and environmental/ climatic interactions during the late Quaternary ...... 49

4.1 Introduction ...... 49 4.2 Human arrival in the Kimberley and occupation trends...... 49 4.3 The Kimberley’s rock art ...... 52 4.4 Aboriginal mythology ...... 56 4.5 Discussion ...... 57

4.5.1 Climatic inferences from rock art iconography, Aboriginal mythology and population densities ...... 57 4.5.2 Anthropogenic impacts on the Kimberley’s climate and environment ...... 63

4.6 Conclusion ...... 64

5 A late Quaternary record of monsoon variability in the northwest Kimberley, Australia ...... 65

5.1 Introduction ...... 65

5.1.1 Mound springs and climate proxies ...... 66

5.2 Regional setting ...... 67 5.3 Materials and methods...... 70

5.3.1 Sample collection ...... 70 5.3.2 Chronology...... 71 5.3.3 Pollen and microcharcoal analysis ...... 71 5.3.4 Sediment analysis ...... 72 5.3.5 Humification analysis ...... 72

5.4 Results ...... 73

5.4.1 Chronology...... 73 5.4.2 Surface pollen ...... 76 5.4.3 Fossil pollen and microcharcoal ...... 81 5.4.4 Sediment analysis ...... 87 5.4.5 Humification ...... 89

5.5 Discussion ...... 90

5.5.1 Mound spring morphology and environmental change at Black Springs ...... 90 5.5.2 Drivers of change ...... 95 5.5.3 Impacts of chronological uncertainty ...... 96

5.6 Conclusions ...... 97

6 Untangling geochronological complexity in organic spring deposits using multiple dating methods ...... 98

6.1 Introduction ...... 98

6.1.1 Conceptual sources of geochronological complexity in organic spring deposits ...... 101 6.1.2 Common chronological issues in organic spring deposits ...... 104

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6.2 Physical setting ...... 108 6.3 Materials and methods...... 109

6.3.1 Core collection and description ...... 109 6.3.2 Carbon-14 dating...... 109 6.3.3 Lead-210 dating ...... 112 6.3.4 Plutonium-239+240 chronostratigraphic markers ...... 112 6.3.5 Supporting chronological information ...... 113

6.4 Results ...... 114

6.4.1 Core lithology ...... 114 6.4.2 Carbon-14 dates ...... 115 6.4.3 Lead-210 profiles and modelled ages ...... 121 6.4.4 Plutonium-239+240 profiles ...... 123

6.4.5 Ln/Tn profiles for BSP02 ...... 125

6.5 Discussion ...... 126

6.5.1 The behaviour of 210Pb and 239+240Pu in organic spring deposits and their utility for developing chronologies ...... 126 6.5.2 The behaviour of different carbon fractions in organic springs ...... 129 6.5.3 Sources of 14C anomalies ...... 132 6.5.4 The feasibility of different carbon fractions for building reliable 14C chronologies in organic spring deposits ...... 138

6.6 Conclusions ...... 139

7 Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years ...... 141

7.1 Introduction ...... 141 7.2 Study sites...... 142 7.3 Materials and methods...... 144

7.3.1 Sample collection and description ...... 144 7.3.2 Geochronology ...... 145 7.3.3 Geochemical analysis ...... 146 7.3.4 Pollen, NPP and micro-charcoal analysis ...... 147

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7.3.5 Statistical methods ...... 148

7.4 Results ...... 149

7.4.1 Geochronology ...... 149 7.4.2 Itrax µXRF elemental geochemistry ...... 152 7.4.3 Pollen, NPPs and micro-charcoal...... 158 7.4.4 Statistical analysis ...... 169

7.5 Discussion ...... 174

7.5.1 Interpretation of Itrax µXRF data ...... 174 7.5.2 IASM variability over the last 14,500 years ...... 177

7.6 Conclusion ...... 186

8 Conclusions and future research directions ...... 188

8.1 Problem statement and research aims ...... 188 8.2 Research findings ...... 189

8.2.1 Aim 1: To develop knowledge of the Kimberley at present to construct a framework for understanding past changes: ...... 189 8.2.2 Aim 2: To assess the current state of understanding regarding late Quaternary (<50,000 yr BP) climate and environmental change in the Kimberley in order to identify knowledge gaps: ...... 190 8.2.3 Aim 3: To ascertain whether organic spring deposits are suitable archives for reconstructing climatic and environmental change in otherwise challenging environments such as the Kimberley (e.g. arid and semi-arid regions): ...... 191 8.2.4 Aim 4: To reconstruct climate and environmental change in tropical northwest Australia during the period spanning the LGIT to present day, and relate changes to potential drivers of climatic variability: ...... 192 8.2.5 Aim 5: To assess whether the Kimberley has experienced changes in past climate and environmental conditions on a regional-scale (i.e. >1000s km2): ...... 193 8.2.6 Aim 6: To relate changes in the Kimberley’s climate and environment since the LGIT to potential drivers of climatic variability...... 194

8.3 Contribution of this research ...... 195 8.4 Thesis limitations ...... 196 8.5 Future research priorities ...... 198

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8.6 Summary ...... 199

Reference list...... 201 Appendices ...... 236

Appendix 1. Submitted journal articles during candidature ...... 236 Appendix 2. Locations of samples mentioned in the text ...... 237 Appendix 3. Pollen (%), micro-charcoal and NPP (concentration and accumulation rates) data for all samples mentioned in the text ...... 238 Appendix 4. Humification data (% transmission and residuals) for BSP00 ...... 255 Appendix 5. LOI data (% organic) for all samples mentioned in text ...... 256 Appendix 6. 210Pb results including age calculations using both the CIC and CRS models...... 260 Appendix 7. 239+240Pu results ...... 261 Appendix 8. Elemental composition (% by weight) of charcoal fragments derived from SEM and EDXA ...... 262 Appendix 9. Ln/Tn data for BSP02 ...... 263 Appendix 10. PCA axis 1 scores for pollen and NPP datasets for all samples mentioned in the text ...... 265

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List of Figures

Chapter 1

Figure 1.1. Flow chart of the thesis structure, linking thesis chapters to research objectives ...... 8

Chapter 2

Figure 2.1. The geographical setting of the Kimberley. Inset shows the location of the area in the larger map in relation to Australia (red square) ...... 11

Figure 2.2. (A) Tectonic units and physiographical divisions of the Kimberley adapted from Wende (1997), Tyler et al. (2012) and Pepper and Keogh (2014). (B) Simplified geological divisions of the Kimberley Basin, depicting various rock units of the Kimberley including the KLS, CV, WS and PS adapted from Brocx and Semeniuk, 2011. (C) Major hydrogeological divisions of the Kimberley in comparison to tectonic units (depicted by solid lines, adapted from panel A). (D) Bioregions of the Kimberley in comparison to tectonic units (depicted by the same colouring shown in panel A) ..... 14

Figure 2.3. Mean annual rainfall in the Kimberley (1990-2005) (adapted from Department of Water, 2010) ...... 15

Figure 2.4. Location of the Kimberley (outlined) in relation to climatic features mentioned in the text (IPWP adapted from Gagan et al., 2004; Pilbara heat low and wind patterns adapted from Kuhnt et al., 2015)...... 17

Figure 2.5. The location of Black Springs, Fern Pool and Gap Springs in relation to the MVGs and the Kimberley Plateau (the extent of which is depicted by the dashed line) ...... 19

Figure 2.6. Black Springs shown in comparison to the surrounding tropical savanna woodland in panel A. Panel B depicts the dense monsoon vine thicket growing on the mound, whilst Panel C depicts the vegetation typical of the fringing wetland (e.g. P. karka and Cyperaceae)……………..20

Figure 2.7. Satellite imagery of Black Springs (Google Earth, 2017). Coring location shown by white cross...... 20

Figure 2.8. A series of three mounds can be seen at Fern Pool in Panel A, whilst typical vegetation growing on these mounds is depicted in Panel B. Upwelling groundwater in the nearby Donkey Creek is shown in Panel C ...... 21

Figure 2.9. Satellite imagery of Fern Pool (Google Earth, 2017). Coring location shown by white cross ...... 22

Figure 2.10. The vegetation at Gap Springs is shown in Panels A – C, with the less topographically distinct nature of the spring depicted in Panels A and B ...... 23

Figure 2.11. Satellite imagery of Gap Springs (Google Earth, 2017). Coring location shown by white cross...... 23

Figure 2.12. The location of Black Springs, Fern Pool and Gap Springs in relation to altitude. The extent of the Kimberley Plateau is depicted by the dashed line...... 24

Chapter 3

Figure 3.1. Location of sites containing records of late Quaternary palaeoclimate and palaeoenvironmental change in the Kimberley and surrounding marine environment. Numbering relates to ID in Table 3.1, with high-resolution records described in Section 3.1 given red, italicised labels. Site 8 is excluded from this map since it is off the Cape Range Peninsula >500 km from the southwest limit of the Kimberley………………………………………………………………….29

Figure 3.2. Sea level change in the Bonaparte Gulf during the LGM and deglacial (De Deckker and Yokoyama, 2009:89). Open circles and triangles represent data from Yokoyama et al. (2000) and Yokoyama et al. (2001a), open squares represent data from van Andel et al. (1967). Black dots represent data from De Deckker and Yokoyama (2009). Errors are depicted by grey shading ...... 31

Figure 3.3. Timor Sea XRF-scanner records illustrating riverine runoff/terrigenous input (ln(K/Ca)) from northwest Australia (data courtesy of Wolfgang Kuhnt). Red arrows indicate increasing monsoon activity ...... 32

Figure 3.4. Weighted Averaging Partial Least Squares estimates of selected climatic parameters based on fossil pollen from core FR10/95-GC17, with vertical lines indicating modern values for each climatic parameter (van der Kaars et al., 2006:887) ...... 33

Figure 3.5. Coral growth records at Cockatoo Island (Solihuddin et al., 2015) and Scott Reef (Collins et al., 2011) (adapted from Solihuddin et al., 2015) ...... 35

Figure 3.6. Terrestrial sediment cores recovered in the Kimberley. The length of the records are depicted by grey bars, with white bars indicating hiatuses ...... 36

Figure 3.7. Stable isotope time series of the KNI-51 (black line) and Ball Gown Cave (grey line) stalagmites, with red arrows on vertical axes depicting IASM activity (increased monsoon strength oriented up) (data sourced from www.ncdc.noaa.gov; Denniston et al., 2013a, 2013b) ...... 38

Figure 3.8. The timing of climatic changes from selected geomorphological records in the Kimberley (from Fitzsimmons et al., 2012:476), including: (a) linear dunes in the Gregory Lakes

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basin (Fitzsimmons et al., 2012); (b) lake and dune records from the Gregory Lakes basin (Bowler et al., 2001); (c) lake highstands at Lake Mulan (Veth et al., 2009); (d) fluvial and lacustrine sediments in the Gregory Lakes basin and Fitzroy River catchment (Wyrwoll and Miller, 2001); and (e) lake and dune records from Lake Woods in the Northern Territory (Bowler et al., 1998) ...... 41

Figure 3.9. Generalised changes in the Kimberley’s monsoon activity and climate over the last 50,000 years. Changes are with respect to the previous time interval: A) Late MIS3 (50,000 – 30,000 yrs BP); B) glacial (30,000 – 18,000 yrs BP); C) deglacial (18,000 – 12,000 yrs BP); D) early-Holocene (12,000 – 8000 yrs BP); E) mid-Holocene (8000 – 4000 yrs BP); and F) late- Holocene (4000 yrs BP – present. The present day Kimberley coastline is outlined in black…..….47

Chapter 4

Figure 4.1. A) Plot of all archaeological 14C dates for the Kimberley and B) frequency of dates (Veth et al., 2017a:5)...... 51

Figure 4.2. Map showing the location of archaeological sites in the Kimberley discussed in the text ...... 51

Figure 4.3 The Kimberley rock art sequence (adapted from Walsh, 1994) ...... 53

Figure 4.4. Characterisation of iconography for each of the six major Kimberley rock art periods initially classified by Walsh (1994). Information adapted from Veth et al. (2017a) and Walsh (2006); chronology adapted from Ouzman et al. (2017). Imagery by Graeme Walsh, courtesy of Takarakka Nowan Kas Rock Art Archive ...... 54

Figure 4.5. Mega-tsunami chronology in the Kimberley, falling within the believed time frame of Wanjina mythology (adapted from Bryant et al., 2007) ...... 57

Figure 4.6. An Irregular Infill Animal period depiction from the Kimberley’s north which bears resemblance to the Greater Bilby (Macrotis lagotis), a species presently found in desert areas to the south (Walsh, 2000) ...... 58

Figure 4.7. A compilation of figures appearing in Gwion period art in the Kimberley, with depictions of hunting with long range spears and macropods. Imagery adapted from Walsh (2000) courtesy of Takarakka Nowan Kas Rock Art Archive ...... 59

Figure 4.8. Kimberley art motifs by period (Veth et al., 2017a:15) ...... 60

Figure 4.9. A compilation of turtle and fish motifs appearing in Painted Hand period art. Imagery adapted from Walsh (2000) courtesy of Takarakka Nowan Kas Rock Art Archive ...... 60

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Figure 4.10. Lightning depicted in Wanjina paintings in a variety of schematised forms (shown in red). Panel A shows the form of more ‘naturalistic’ lightning depicted as zig zag lines emanating from the shoulder of Early Wanjinas. Panels B and D have blown white spots incorporated in the lines of lightning above and radiating from their headdress. Panel E has a heavy secondary arch of lighting draped over its headdress. Panels C and F show schematised “classic” Wanjinas, F with children and followers painted in horizontal alignment, with lightning ‘arch’ under head. Imagery by Grahame Walsh, courtesy of Takarakka Nowan Kas Rock Art Archive ...... 61

Figure 4.11. Modelled October - April response to vegetation change: (a) leaf area index;(b) sensible heat flux; (c) latent heat flux; (d) ground temperature; (e) surface air temperature; (f) precipitable water; (g) vertical velocity; (h) precipitation; and (i) evaporation (Wyrwoll and Notaro, 2014:112)……………………………………………………………………………………………64

Chapter 5

Figure 5.1. Location of Black Springs in relation to (A) Australian climatic features (IPWP adapted from Gagan et al. (2004) and Pilbara heat low and wind patterns adapted from Kuhnt et al. (2015)), (B) regional hydrogeologic units of the North Kimberley Bioregion, and (C) satellite imagery of the Black Springs study site - the mound is visible as the dark green patch in the centre of the image (Google Earth, 2017)...... 69

Figure 5.2. Photographs of Black Springs. The top plate shows mound spring vegetation including Ficus sp., M. viridiflora and a fern understorey; the centre plate shows the fringing P. karka; the bottom plate shows surrounding tropical savanna grassland ...... 70

Figure 5.3. Bayesian age model generated for BSP00. The age model was generated using Bacon 2.2 (Blaauw and Christen, 2011). The blue dots represent the 14C ages………………………..….76

Figure 5.4. (A) Map showing the vegetation zones of Black Springs. The position of surface sample locations is indicated on the panel, while the composition of each surface sample is indicated in the pie charts. (B) PCA biplot of the surface samples shown in panel A………………………………80

Figure 5.5. Pollen percentage diagram of the Black Springs core (pteridophytes, Myrtaceous, grass, tropical savanna and wetland taxa included within the total pollen sum (dot = ≤1.5%)). Also shown are the results of cluster analysis which aided the identification of the eight pollen zones shown (labelled BSP1 – BSP8) ...... 84

Figure 5.6. PCA biplot of the Black Springs fossil and modern pollen data ...... 86

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Figure 5.7. Overview pollen diagram for Black Springs, with LOI and humification results and pollen zones BSP1 – BSP8 indicated. Pollen, charcoal and Pseudoschizaea accumulation rates and concentrations are also plotted...... 88

Figure 5.8. Black Springs humification record plotted against age. The solid (red) line shows % transmission data smoothed (with a 3-point moving average) and normalised to LOI. The dashed (blue) line shows the detrended and smoothed residuals. Inferred wet and dry phases are indicated by grey shaded areas. Note - only oscillations from ~9600 cal. yr BP to present are inferred as representing changes in bog surface wetness (see main text for further details) ...... 89

Chapter 6

Figure 6.1. Potential sources of geochronological complexity in organic springs via (1) aeolian and alluvial input, (2) root growth and washdown of organic substances and sediment, (3) upwelling groundwater, (4) bioturbation, (5) self-mulching, slumping, and (6) weathering…………………103

Figure 6.2. Carbon-14 chronologies from (A) Dalhousie Springs, Australia (Boyd, 1990b), (B) Uitzigt, South Africa (Butzer, 1984a, 1984b), (C) Ulungra Springs, Australia (Dodson and Wright, 1989), (D) Black Springs, Australia (Field et al., 2017), (E) Warburton Spring, Australia (Fluin et al., 2013), (F) EDSA, Jordan (Rambeau, 2010), (G) Scot, South Africa (Scott, 1982b), (H) Tate Vondo, South Africa (Scott, 1987), (I) Meriba Spring, South Africa (Scott, 1988), (J) Rietvlei, South Africa (Scott and Vogel, 1983), (K) Florisbad Spring, South Africa (Scott and Nyakale, 2002) and (L) Wonderkrater, South Africa (Scott et al., 2003) ...... 105

Figure 6.3. Carbon-14 chronologies from (M) Zawadówka, Poland (Dobrowolski et al., 2005), (N) Radzików, Poland (Dobrowolski et al., 2012), (O) Komarów, Poland (Dobrowolski et al., 2016), (P) Melaleuca Tin Mine, Australia (Macphail et al., 1999), (Q) Bobolice, Poland (Mazurek et al., 2014), (R) Orgartowo, Poland (Mazurek et al., 2014), (S) Broadmeadow Swamp, Australia (van de Geer et al., 1986), (T) Mowbray Swamp, Australia (van de Geer et al., 1986) and (U) Pulbeena Swamp, Australia (van de Geer et al., 1986) ...... 106

Figure 6.4. The location of springs plotted in Figure 6.2 and Figure 6.3 ...... 107

Figure 6.5. Location of the three springs investigated in this study. An overview map is shown in panel (A), whilst satellite imagery of the three sites are shown for Black Springs (BSP02/BSP00) in panel (B), Fern Pool (FRN02) in panel (C), and Gap Springs (ELZ01) in panel (D). Coring locations are indicated by a white cross ...... 108

Figure 6.6. Generalised stratigraphy, organic content and photographs of cores BSP02, FRN02 and ELZ01 ...... 115 xxiv

Figure 6.7. Calibrated 14C dates for (A) BSP02, (B) BSP00, (C) FRN02 and (D) ELZ01. The 2σ calibrated age ranges are plotted, however in most cases these are not visible at the plotted resolution. These age ranges are provided in Table 6.1…………………………………………..118

Figure 6.8. Supported and unsupported 210Pb activities for (A) BSP02, (B) FRN02 and (C) ELZ01. The grey bar at 0 Bq/kg highlights apparent negative unsupported 210Pb activities. X-axis error bars represent the 2σ error, y-axis error bars represent the sampling depth range ...... 121

Figure 6.9. Lead-210 derived age models for (A) BSP02 and (B) ELZ01 ...... 123

Figure 6.10. Plutonium-239+240 depth profiles for BSP02 and ELZ01. X-axis errors bars represent the 1σ error, y-axis error bars represent sampling depth range. The grey box indicates the potential range of depths over which peak 239+240Pu activity may occur in ELZ01 given the sampling resolution and activity profile ...... 124

Figure 6.11. Quartz (BSL) and feldspar (IRSL) Ln/Tn profiles within BSP02. The organic content and photograph of this core are included for comparison ...... 125

Figure 6.12. The comparison of 210Pb chronologies and 239+240Pu chronostratigraphic information for (A) BSP02 and (B) ELZ01 ...... 127

Figure 6.13. Quartz (BSL) and feldspar (IRSL) Ln/Tn profiles for BSP02 alongside 14C dates from all carbon fractions (macro-charcoal, SPAC, pollen and roots). A possible growth hiatus region is depicted by the grey line, the region of increased variability in the Ln/Tn data is indicated by shading, and the shift to lower Ln/Tn towards the base of the core is defined by brackets……….130

Figure 6.14. SEM micrographs of charcoal structure from macro-charcoal 14C samples from BSP02 core: (A) OZT910, (B) OZT911, (C) OZT912, (D) OZT913; FRN02 core: (E) OZT916, (F) OZT917, (G) OZT918, (H) OZT919; ELZ core: (I) OZT914, (J) OZT915; and entire fragments from (K) OZT919 and (L) OZT910 ...... 135

Figure 6.15. Elemental composition (% by weight) of charcoal fragments from macro-charcoal 14C samples in Kimberley springs. Samples are plotted alongside their calibrated ages (shown as grey bars) and depth-sequences (shown as orange lines) for comparison ...... 136

Chapter 7

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Carson Volcanics (CV; dark grey), Warton Sandstone (WS; white) and Pentecost Sandstone (PS; light grey) adapted from Brocx and Semeniuk (2011). (C) Overview map of northern Australia, location of panels (A) and (B) are indicated by the black square ...... 144

Figure 7.2. Bayesian age-depth models generated for cores (A) BSP02, (B) FRN02 and (C) ELZ01 using Bacon 2.2 (Blaauw and Christen, 2011). The upper panels indicate the number of iterations performed, accumulation rates and memory used in the generation of each model………………152

Figure 7.3. Selected Itrax µXRF scanner records for BSP02 (grey lines are raw data, black lines depict a 9-point moving average with ~50 year resolution) and Cr Inc/Coh plotted alongside generalised stratigraphy, core photograph and LOI……………………………………………….155

Figure 7.4. Selected Itrax µXRF scanner records for FRN02 (grey lines are raw data, black lines depict a 9-point moving average with ~50 year resolution) and Cr Inc/Coh plotted alongside generalised stratigraphy, core photograph and LOI ...... 156

Figure 7.5. Selected Itrax µXRF scanner records for ELZ01 (grey lines are raw data, black lines depict a 5-point moving average with ~50 year resolution) and Cr Inc/Coh plotted alongside generalised stratigraphy, core photograph and LOI ...... 157

Figure 7.6. The representation of A) spring taxa, B) wetland taxa, D) Eucalyptus, and E) Poaceae through time at Black Springs (blue), Fern Pool (grey) and Gap Springs (green). Spring/wetland taxa ratios are shown in panel C, whilst Eucalyptus/Poaceae ratios are shown in panel F ...... 159

Figure 7.7. Summary pollen diagram of BSP02 (pteridophytes, wetland and spring taxa included within the local pollen sum; grass and tropical savanna taxa included within the regional pollen sum), with generalised stratigraphy, key pollen taxa (>5 % in at least one sample) and accumulation rates for pollen, charcoal and NPPs plotted. Also shown are the results of CONISS analysis which guided the identification of the six pollen zones shown (labelled BSP02_01 – BSP02_06)...... 162

Figure 7.8. Summary pollen diagram of FRN02 (pteridophytes, wetland and spring taxa included within the local pollen sum; grass and tropical savanna taxa included within the regional pollen sum), with generalised stratigraphy, key pollen taxa (>5 % in at least one sample) and accumulation rates for pollen, charcoal and NPPs plotted. Also shown are the results of CONISS analysis which guided the identification of the five pollen zones shown (labelled FRN02_01 – FRN02_05) ...... 165

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rates for pollen, charcoal and NPPs plotted. Also shown are the results of CONISS analysis which guided the identification of the five pollen zones shown (labelled ELZ01_01 – ELZ01_05)...... 168

Figure 7.10. Time series of PCA axis 1 scores for Itrax µXRF, pollen, and NPP data at each site. The black lines depict the data on their age models as presented in Figures 7.3 - 7.9. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 10,000 iterations of age-depth modelling ...... 169

Figure 7.11. MCEOF Si/Ti synthesis for BSP02, FRN02 and ELZ01. Time series of local Si/Ti records at each site presented in blue, with the black lines depicting data on their age models as presented in Figures 7.3 - 7.5. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Y axes are oriented to show higher Si/Ti ratios plotting upwards. The results of the MCEOF proxy Si/Ti synthesis are presented in red, with the black line depicting the median, dark red shading = 90% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 10,000 iterations of age-depth modelling ...... 173

Figure 7.12. MCEOF Pseudoschizaea synthesis for BSP02, FRN02 and ELZ01. Time series of local Pseudoschizaea records at each site presented in blue, with the black lines depicting data on their age models as presented in Figures 7.7 - 7.9. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Y axes are oriented to show higher Pseudoschizaea accumulation rates plotting upwards. The results of the MCEOF proxy Pseudoschizaea synthesis are presented in red, with the black line depicting the median, dark red shading = 90% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 2000 iterations of age-depth modelling ...... 174

Figure 7.13. Screeplot of variance explained vs. axis number for MCEOF analysis of A) Si/Ti and B) Pseudoschizaea regional EOF1 scores. Solid black line = mean solution from A) 10,000 and B) 2,000 iterations, solid grey line = 1σ error, grey dashed line = 2σ error. Red line = broken stick model, used as a test of axis significance (Bennett, 1996) ...... 174

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reduction in runoff, recharge and spring discharge; E) 2600 – 1000 cal. yr BP with a very weak or absent summer monsoon and the possible northward contraction of Tropical Eucalypt Woodland/Grassland (MVG 12) and expansion of drier vegetation communities; and F) 1000 cal. yr BP to present with ameliorating climatic conditions and a more active summer monsoon, resulting in runoff, recharge, and spring discharge ...... 186

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List of Tables

Chapter 3

Table 3.1. Metadata for late Quaternary palaeoclimate and palaeoenvironmental change in the Kimberley and northwest Australia ...... 27

Table 3.2. Summary of all published records in the Kimberley and offshore from the late MIS3 to present ...... 44

Chapter 4

Table 4.1. Possible chronology of climate and environmental changes inferred from the Kimberley’s rock art, archaeological record and Aboriginal mythology (imagery adapted from Figures 4.6 - 4.10) ...... 62

Chapter 5

Table 5.1. 14C dates and calibrated ages for Core BSP00. Carbon-14 dates incorporated in the age model are shown in bold, italicised text ...... 75

Table 5.2. Some information on pollen taxa encountered in the surface and core samples ...... 78

Table 5.3. Summarised wet and dry shifts observed in the humification record (approximate depths and ages). The wettest and driest period is indicated by bold, italicised text ...... 90

Chapter 6

Table 6.1. 14C dates and calibrated ages for all samples from cores BSP02, FRN02, ELZ01 and BSP00...... 116

Table 6.2. Polonium-210 and 226Ra activities of groundwater at Black Springs, Fern Pool and Gap Springs ...... 128

Chapter 7

Table 7.1. 14C dates and calibrated ages for all samples from cores BSP02, FRN02 and ELZ01 ... 150

Table 7.2. Correlation matrices for selected elements and ratios in BSP02, FRN02 and ELZ01. Strong positive correlations (r ≥ 0.7) are indicated by shaded, italicised text whilst strong negative correlations (r ≤ -0.7) are indicated by shaded, bold text ...... 153

Table 7.3. Indicative values of the NPPs encountered in this study (adapted from Carrión and Navarro, 2002)……………………………………………………………………………………..159

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Table 7.4. Species scores for variables selected for PCA for each dataset at each of the three sites (Itrax µXRF, pollen, and NPPs)……………………………………………………………….…..170

List of Equations

3 (1) ρ = Dry bulk density (g/mL); Swm = Sample wet mass (g); Swv = Sample wet volume (m ); θs = Sample moisture content (%) ...... 112

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List of abbreviations used in the thesis

µXRF Micro X-ray fluorescence 133Ba Barium-133 137Cs Caesium-137 210Pb Lead-210 209Po Polonium-209 210Po Polonium-210 242Pu Plutonium-242 239+240Pu Plutonium-239+240 14C Radiocarbon 226Ra Radium-226 233U Uranium-233 AAA Acid-alkali-acid ABOX-SC Acid base oxidation-stepped combustion AMS Accelerator mass spectrometry ANSTO Australian Nuclear Science and Technology Organisation B/A Bølling-Allerød

BaSO4 Barium sulfate BSL Blue light stimulation

C3H8O3 Glycerol

(CH3CO)2O Acetic anhydride Cal. yr BP Calendar years before present CIC Constant initial concentration

CO2 Carbon dioxide CRS Constant rate of supply CV Carson Volcanics D/O Dansgard-Oeschger DCA Detrended Correspondence Analysis EASM East Asian Summer Monsoon EDXA Energy dispersive X-ray analysis ENSO El Niño Southern Oscillation EOF Empirical orthogonal function

Fe(OH)3 Iron(III) oxide-hydroxide

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H0 Younger Dryas H1 Heinrich Event 1

H2O2 Hydrogen peroxide

H2SO4 Sulphuric acid HCl Hydrochloric acid

HCl:HNO3 Aqua regia HF Hydrofluoric acid

HNO3 Nitric acid HPGe High purity germanium HyPy Hydrogen pyrolysis IASM Indonesian-Australian summer monsoon Inc/Coh Incoherence/coherence scattering ratio IOD Indian Ocean Dipole IPO Inter-decadal Pacific Oscillation IPWP Indo-Pacific Warm Pool IRMS δ13C Isotope Ratio Mass Spectrometer ITCZ Inter-tropical Convergence Zone KLS Kimberley Sandstone KOH Potassium hydroxide LGIT Last Glacial-Interglacial Transition LGM Last Glacial Maximum

Ln Natural luminescence signal

Ln/Tn Natural sensitivity-corrected luminescence LOI Loss-on-ignition MCEOF Monte Carlo Empirical Orthogonal Function MIS3 Marine Isotope Stage 3 MJO Madden-Julian Oscillations MVG Major Vegetation Group

Na4P2O7 Tetrasodium pyrophosphate PCA Principal Components Analysis SEAPAC Southeast Asia, Australia and the Pacific SPAC Stable polycyclic aromatic carbon SSTs Sea surface temperatures

Tn Test signal

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1 Introduction

1.1 Introduction to thesis

The monsoonal Kimberley region in northwest Australia is vast and remote, encompassing high rainfall tropics, savanna and semi-arid deserts, punctuated by gorges, mesas, rainforest, mangroves and swamps (Government of Western Australia, 2011). The region is renowned for its rich archaeological legacy, and arguably one of the world’s most significant and complex collections of rock art (Walsh, 2000; Welch, 2016), providing evidence of human occupation for ~50,000 years (e.g. Hiscock et al., 2016). Consequently there is a significant volume of ongoing research into the Kimberley’s rock art and archaeology. However, knowledge of climatic and environmental change over the late Quaternary in northwest Australia, particularly for the time-period spanning human occupation, is limited.

This thesis develops new, high-resolution records of late Quaternary climatic and environmental change for the Kimberley region, whilst also assessing the suitability of organic spring deposits as critical archives in arid and semi-arid environments such as northwest Australia. This chapter provides context for the current gaps in knowledge, followed by a statement of the thesis aims and objectives. It also outlines a generalised research methodology, thesis structure, and subsequent chapter content.

1.1.1 Context of this research

Across northern Australia there is evidence of significant climate and environmental change during the late Quaternary (Reeves et al., 2013). These include cooler conditions during the Last Glacial Maximum (LGM), rapid flooding of the continental shelf during the deglacial, and a trend to wetter climates into the Holocene, punctuated by millennial-scale variability – particularly during the late- Holocene (Reeves et al., 2013). Such changes may have impacted human populations in a number of ways, e.g. by challenging the ability of societies to adapt. For instance, rapid climate change has been cited as the driver behind the collapse of several civilisations in a number of global locations (Diamond, 2005), such as an abrupt weakening of the Asian monsoon at approximately 4400 yrs BP thought to be responsible for the collapse of Neolithic Cultures on China’s Central Plain (Wenxiang and Tungsheng, 2004). In northern and central Australia, there is evidence that monsoon variability forced pre-historic Aboriginal populations to develop increased mobility and new technologies to adapt to changing resource availability such as food and water (Williams et al., 2010). Whilst there is archaeological evidence for significant changes in human occupation of the Kimberley over the last ~50,000 years, e.g. periods of abandonment across a mosaic of sites (e.g. O’Connor and Veth,

1 Chapter 1

2006), and dramatic changes in rock art iconography and information exchange behaviours indicative of past environmental and climatic changes (Walsh, 2006; Veth et al., 2017a), there is limited environmental or climatic context with which to interpret these. Understanding the late Quaternary climate of this region is also essential for gaining a complete understanding regarding human occupation patterns in central Australia, as the hydro-climatology of this region is heavily influenced by the northwest Australian monsoon (Smith et al., 1991; Smith, 2009; Fitzsimmons et al., 2013).

The lack of knowledge regarding long-term monsoon activity in northwest Australia limits overall understanding of the global climate system. The Kimberley’s climate is dominated by the Indonesian-Australian summer monsoon (IASM), which is part of a wider monsoon system spanning the Indo-Pacific Warm Pool (IPWP) and the Maritime Continent, incorporating the East Asian Summer Monsoon (EASM) (Denniston et al., 2013a). This wider region acts as a global heat source which plays a major role in driving planetary scale circulation (Keenan et al., 1989, 2000) and is a primary source of latent heat release driving the Southern and Madden-Julian Oscillations (MJO) (McRobie et al., 2015). Therefore at present, there is an incomplete understanding regarding the interactions between a number of monsoon systems, and ultimately planetary scale circulation, over long timescales.

Whilst it is important to understand the nature of tropical climate change throughout the late Quaternary, in particular the Last Glacial-Interglacial Transition (LGIT) since this enables insight into the Earth’s climate system during a significant climatic period, (Reeves et al., 2013), palaeoclimate data can also be used to test the robustness of models which predict projected climate change (Henderson et al., 2009). New palaeoclimate records from the Kimberley are therefore critical for testing predictions of future dynamics of the IASM, the wider monsoon region, and global low latitude atmospheric circulation.

1.2 Archives of late Quaternary environmental and climatic change in the Kimberley

Despite the Kimberley’s vast size, only a handful of high-resolution published records of environmental and climatic change exist for the region (e.g. McGowan et al., 2012; Denniston et al., 2013a, 2013b; Proske et al., 2014; Denniston et al., 2015; Proske, 2016). Just one of these records extends past the Holocene (e.g. Denniston et al., 2013a), and several of the others are either short (e.g. Denniston et al., 2015), contain hiatuses (e.g. Proske et al., 2014; Proske, 2016), or are limited to coastal environments (e.g. Proske et al., 2014; Proske, 2016). The lack of long, continuous palaeoenvironmental records from northwest Australia stands in stark contrast to eastern and southern Australia where many such records have been developed, e.g. in Tasmania (e.g. Colhoun 2 Chapter 1 et al., 1982, 1999), Victoria (e.g. D’Costa et al., 1989; Edney et al., 1990; Kershaw et al., 2007b), New South Wales (e.g. Dodson and Wright, 1989; Sweller and Martin, 2001; Black et al., 2006), and Queensland (e.g. Longmore and Heijnis, 1999; Donders et al., 2006; McGowan et al., 2008; Moss et al., 2013). Whilst some long records for the Australian tropics exist (e.g. Dimitriadis and Cranston, 2001; Haberle, 2005; Tibby and Haberle, 2007; Kershaw et al., 2007a; Burrows et al., 2016), these have been derived from wetter regions such as the Atherton Tablelands, and as such there is a pressing need to develop records from the drier regions including the savanna that comprises a large part of the tropics (Reeves et al., 2013).

The lack of continuous, high-resolution records from the Kimberley is primarily due to the monsoonal climate, where high evaporation rates and a lack of rain during the dry season limits perennial water sources (e.g. extensive lakes or wetlands) which may preserve robust sedimentary records typically used in “classic” palaeoenvironmental and climatic research. Records from seasonal wetlands and ephemeral lakes are also likely to be compromised by unconformities and poor fossil preservation as a result of desiccation, oxidation and aeolian deflation during dry phases, and/or scouring during periods of heavy rainfall (Head and Fullager, 1992; Magee et al., 1995). In addition to the small number of high-resolution records from the Kimberley, palaeoclimate and environmental data is also available from other archives including archaeological sites and geomorphology. However, the information that can be derived from these records is limited by their discontinuous nature (e.g. Jennings, 1975; Thom et al., 1975; Wyrwoll et al., 1986, 1992; Lees, 1992a, 1992b; Lees et al., 1992; Wende et al., 1997; Bowler et al., 2001; Wyrwoll and Miller, 2001; Veth et al., 2009; Fitzsimmons et al., 2012; Fujioka et al., 2014) and/or coarse temporal resolution (e.g. McConnell and O’Connor, 1997; Vannieuwenhuyse et al., 2017). Additional information regarding the environmental and climatic change in the Kimberley may be derived from offshore records (e.g. van Andel and Veevers, 1967; van Andel et al., 1967; van der Kaars, 1991; Wang et al., 1999; van der Kaars and De Deckker, 2002; Kershaw et al., 2002; van der Kaars et al., 2006; Kuhnt et al., 2015), and whilst these records are somewhat useful in providing an insight into late Quaternary environments of the region, they are limited by their lower temporal resolution and location.

1.2.1 Organic spring deposits

Although there are few perennial lakes or wetlands in the Kimberley region, there are perennial or ephemeral springs with organic deposits (e.g. Vernes, 2007; Government of Western Australia, 2014). In several arid and semi-arid environments, organic spring deposits have been used as an alternative where there are few conventional sites for palaeoenvironmental/climatic research (e.g.

3 Chapter 1

Scott, 1982a, 1982b; Scott and Vogel, 1983; Scott, 1988; Dodson and Wright, 1989; van Zinderen Bakker, 1989; Boyd, 1990b; Scott and Cooremans, 1990; Scott and Nyakale, 2002; Owen et al., 2004; Rambeau, 2010; Fluin et al., 2013; Truc et al., 2013), including in the Kimberley (McGowan et al., 2012; Field et al., 2017). However, there are a number of complications in developing reliable chronologies for these archives, making robust environmental and climatic interpretations difficult (Field et al., 2018). The ability to build reliable chronologies from organic spring deposits is therefore essential in unlocking the Kimberley’s past, and in enabling researchers in other arid and semi-arid locations to obtain accurate, high-resolution palaeoclimate and environmental records.

1.3 Thesis resolution

1.3.1 Problem statement

A number of research problems exist that are relevant to understanding the Kimberley’s past climate and environments, and in using organic spring deposits to do so, including:

 There are scarce continuous, high-resolution records of palaeoclimatic and palaeoenvironmental change from the Kimberley;

 There is a lack of “classic” archives of palaeoenvironmental/palaeoclimate conditions in the Kimberley e.g. lakes and extensive wetlands due to the extreme seasonality in the region. Those records that do exist may be compromised by chronological hiatuses, oxidation and unconformities due to climatic variability; and

 Whilst organic spring deposits located in arid and semi-arid regions (including the Kimberley) offer an alternative to “classic” sedimentary archives, previous research indicates that records from these otherwise promising settings is generally compromised by problematic chronological control, particularly pertaining to radiocarbon dating.

4 Chapter 1

1.3.2 Aims and objectives

This thesis has six aims which seek to address the problem statement:

1. To develop knowledge of the Kimberley at present to construct a framework for understanding past changes;

2. To assess the current state of understanding regarding late Quaternary (<50,000 yr BP) climate and environmental change in the Kimberley in order to identify knowledge gaps;

3. To ascertain whether organic spring deposits are suitable archives for reconstructing climatic and environmental change in otherwise challenging environments such as the Kimberley (e.g. arid and semi-arid regions);

4. To reconstruct climate and environmental change in tropical northwest Australia during the period spanning the last 50,000 years;

5. To assess whether the Kimberley has experienced changes in past climate and environmental conditions on a regional-scale (i.e. >1000s km2); and

6. To relate changes in the Kimberley’s climate and environment during the last 50,000 years to potential drivers of climatic variability.

Each of the research aims will be addressed through the following objectives:

1. Review the Kimberley’s current climate, geology, hydrology and environments, including the distribution of known organic spring deposits. This objective will identify whether springs with characteristics suitable for developing new records are located within the region for use in objectives 4 and 6;

2. Review existing published records of late Quaternary environmental and climatic change in the Kimberley and offshore. This objective will provide a justification for developing new records in this region (objectives 4 and 6);

3. Review existing archaeological and rock art data, alongside literature regarding Aboriginal mythology in the region, to gather additional evidence of human-environmental interactions in the region. This objective will provide additional justification for developing new records in this region (objectives 4 and 6);

4. Develop new records of environmental and climatic change over the last 50,000 years using organic spring deposits in the Kimberley. This objective will also ascertain whether organic spring deposits in the region contain proxies amenable to palaeoenvironmental/climatic

5 Chapter 1

research, and address deficiencies in the current understanding of the region’s palaeoclimate identified in objective 2;

5. Identify the potential and limitations in the use of organic spring deposits as a palaeoenvironmental and palaeoclimate archive;

6. Develop a protocol for building robust chronologies in organic spring deposits. This protocol will address the primary limitations outlined in objective 5;

7. Compare climatic and environmental records spanning the last 50,000 years in the Kimberley. This objective will utilise records developed from three organic spring deposits in the region (objective 4); and

8. Identify potential drivers of climatic variability inferred from the records, and analyse the spatial and temporal changes identified from objective 4 in the context of these drivers. This objective will utilise current climate drivers in northwest Australia outlined in objective 1.

1.4 Generalised research approach

This research seeks to accomplish two primary goals. Firstly, it aims to reconstruct climatic and environmental change in the Kimberley over the last ~50,000 years and relate these to drivers of change. Secondly, it will utilise relatively novel archives to do so – organic spring deposits – and will assess their suitability as settings for palaeo research. This research will provide the first continuous, high-resolution records of palaeoclimatic and environmental change in the Kimberley spanning a period from present day into the late Pleistocene, improving understanding of long-term climate change in this region and the wider IASM region. This research will also provide a protocol for working with organic spring deposits by developing a method by which robust chronologies can be obtained for their sediments. Given that organic spring deposits are potentially useful palaeoenvironmental archives in many settings where “classic” archives are scarce, this knowledge is essential if we are to develop continuous, high-resolution records of change in global locations (e.g. arid and semi-arid environments) which are currently considered challenging for this type of research.

This thesis developed new records for the Kimberley by coring the sediments of three organic springs located along a ~100 km transect in the Kimberley (Black Springs, Fern Pool and Gap Springs). Proxies successfully utilised from these sediments include: pollen for reconstructing predominantly local vegetation changes; micro-charcoal for reconstructing local and regional fire activity; and non-pollen palynomorphs (NPPs), peat humification, elemental geochemistry (Itrax micro X-ray fluorescence (µXRF) core scanning), and loss-on-ignition (LOI) for reconstructing

6 Chapter 1 changes in spring hydrology and morphology. Detailed methodologies for these proxy analyses are presented in Chapters 5 and 7.

A protocol for obtaining robust chronologies from organic spring deposits is developed via geochronological investigation of the three springs. Geochronological techniques include radiocarbon (14C) dating of different carbon fractions, lead-210 (210Pb) dating, the application of plutonium-239+240 (239+240Pu), as well as novel, high spatial resolution, luminescence techniques

(natural sensitivity-corrected luminescence (Ln/Tn) signals). Carbon fractions dated include bulk sediment, pollen concentrate, macro-charcoal, and roots treated with the acid-alkali-acid (AAA) technique, and stable polycyclic aromatic carbon (SPAC) treated with hydrogen pyrolysis (HyPy). A detailed methodology for this geochronological investigation is presented in Chapter 6.

Finally, a comparison of the three records to partition regional and local factors is developed via statistical techniques including Principal Components Analysis (PCA) and Monte Carlo Empirical Orthogonal Function (MCEOF) analysis. The age uncertainty in each of the three records is accounted for in order to determine genuine inter-site coherency. A detailed methodology for these statistical approaches is presented in Chapter 7.

1.5 Thesis structure

This thesis contains six chapters which address the research objectives, including three review chapters followed by three chapters presenting the outcomes of the research, within which more detailed methodologies are embedded. This is followed by a synthesis of these outcomes and a conclusion (Chapter 8). Figure 1.1 outlines the thesis structure, linking individual chapters to research objectives.

7 Chapter 1

Figure 1.1. Flow chart of the thesis structure, linking thesis chapters to research objectives

Chapter 2 provides detail on the physical setting of the Kimberley, including geology, hydrology, environment and climate. Chapter 3 provides a review of the palaeoenvironmental and palaeoclimatic data that currently exists for the region, focusing on the period spanning the last ~50,000 years, whilst Chapter 4 examines the anthropogenic history of the Kimberley for this time

8 Chapter 1 period and interactions between humans and the environment/climate. Chapters 5, 6 and 7 constitute two stand-alone publications and one in-review manuscript, although minor alterations have been made from the published/submitted manuscripts to increase continuity between chapters and to minimise repetition. Chapter 5 presents the results of pollen, humification and sedimentological analysis from Black Springs (core BSP00) in the northwest Kimberley to provide a continuous record of monsoon activity in the region, and provides some context for the changes interpreted from this record. Chapter 6 presents the results of a geochronological analysis of the three springs across the Kimberley (cores BSP02, FRN02 and ELZ01), serving both as a review of dating spring sediments, and in order to establish a protocol for building reliable chronologies in these critical archives. Chapter 7 combines the result of Itrax µXRF, pollen, micro-charcoal and NPP analysis from three springs (cores BSP02, FRN02 and ELZ01) across the Kimberley in order to provide a robust regional-scale reconstruction of change given that regional and local signals are difficult to determine from single-site studies. Chapter 7 then produces a conceptual reconstruction of climate and environmental change in Australia’s northwest since the LGIT, and links changes inferred from the three springs to potential climatic drivers. Finally, Chapter 8 synthesises the outcomes of this research, outlines limitations, and identifies future research priorities.

9 Chapter 2

2 Regional setting

2.1 Introduction and geographical setting

The Kimberley is the northernmost region of the state of Western Australia, covering an area of ~424,500 km2 (Government of Western Australia, 2011). It is bound by the Timor Sea, Indian Ocean (including the Admiralty, Cambridge and Joseph Bonaparte Gulfs, as well as the Camden, King, Yampi and York Sounds), the Northern Territory, and the Tanami and Great Sandy deserts to the north, west, east and south respectively (Figure 2.1). At present approximately 12% of the region is allocated as Aboriginal reserves, ~5% as National Parks and conservation reserves, ~25% as unallocated Crown land, and the remaining area as pastoral and other leases (Government of Western Australia, 2011). Sea levels were ~120 m lower during the Last Glacial Maximum (LGM) than at present, with an increased exposure of continental shelf reducing the Joseph Bonaparte Gulf located immediately to the north of the region to the Bonaparte “Lagoon” (van Andel and Veevers, 1967; Yokoyama et al., 2001a). Rising sea levels from 18,000 yrs BP during the deglacial began to flood the continental shelf, connecting the Bonaparte Lagoon to the Timor Sea once again (van Andel and Veevers, 1967). This chapter presents a review of the physical setting of the Kimberley providing context for the interpretations made in Chapters 5 - 7, including the present geology, geomorphology, hydrogeology, vegetation and climate, including more detailed information regarding the specific study sites.

10 Chapter 2

Figure 2.1. The geographical setting of the Kimberley. Inset shows the location of the area in the larger map in relation to Australia (red square)

2.2 The Kimberley’s geology, geomorphology and hydrogeology

The Kimberley’s geological history is complex, having formed ~2 billion years ago (Tyler et al., 2012). In geological terms, the Kimberley is defined by the Precambrian Kimberley Block (and overlying Proterozoic Basin and Palaeoproterozoic Plateau) in the north, the King Leopold and Halls Creek Orogens which form the Southern Kimberley Ranges to the southwest (King Leopold Range) and southeast (Durack Range) (Pepper and Keogh, 2014) (Figure 2.2A), whilst the Dampier Peninsula to the west is geologically distinct (Lau et al., 1987). The Kimberley Plateau is the dominant geological entity within the region, and is broadly divided into the King Leopold Sandstone (KLS) and Carson Volcanics (CV) in the west, and Pentecost (PS) and Warton Sandstones (WS) in the east (Brocx and Semeniuk, 2011) (Figure 2.2B). The altitude of the Plateau predominantly ranges between 40 – 600 m above sea level, with the highest elevation being 854 m (Boden and Given, 1995) (Figure 2.12). It is predominantly formed of Palaeoproterozoic sandstones, siltstones, mudstones and basalts (occasionally with associated surface lateritic

11 Chapter 2 duricrusts) (Tille, 2006), although the majority of the outcropping rocks are Kimberley Group sandstones (Brocx and Semeniuk, 2011). The topography associated with the KLS in the western Plateau is particularly rugged and dissected, although there are also significant basalt outcrops comprising areas of lower relief (Wende, 1997). A number of scarps and mesas are located within the eastern Plateau, predominantly on gently dipping sedimentary rocks (Wende, 1997). The rocks within the King Leopold and Halls Creek provinces, by contrast, are extensively folded and deformed with fault activity and volcanic intrusions (Pepper and Keogh, 2014), and are predominantly comprised of metamorphosed granites, quartzo-feldspathic volcanic rocks and schist (Griffin and Myers, 1988). The topography of these provinces is characterised by mountain systems with sheer relief and parallel ridges (e.g. the King Leopold and Durack Ranges) (Pepper and Keogh, 2014) (Figure 2.2A).

The Kimberley’s major hydrogeological divisions also broadly correspond with the underlying geology, with the Kimberley Plateau, King Leopold and Halls Creek Orogens characterised by three fractured rock provinces (Kimberley, Halls Creek and Tanami), and the extensive Canning, Ord- Victoria and Bonaparte sedimentary basins located to the west and east (Department of Water, 2010) (Figure 2.2C). Aquifers within the fractured rock provinces are localised, highly variable and of low productivity by comparison to those of the sedimentary basins which are extensive and productive (Department of Water, 2010; Brodie et al., 1998). Freshwater seepages from these aquifers support springs throughout the region, several of which are classified as Threatened Ecological Communities (TECs) located within both the fractured rock province (e.g. Black Springs), and within the more extensive sedimentary basins (e.g. Mandora Mounds, Dragon Tree Soak, Bunda Bunda Springs, and Big Springs) (Government of Western Australia, 2014). However, numerous other organic springs not classified as TECs have been recorded throughout the Kimberley (e.g. Vernes, 2007), or are known to local landowners but remain unrecorded. Groundwater recharge to these springs is dependent on location, with recharge from the fractured rock aquifers typically localised and immediate (Geoscience Australia, 2017). Regardless of groundwater residence time, outflow at any of these springs will be related to precipitation since pressure from meteoric recharge will be transmitted through the aquifer (McCarthy et al., 2010).

2.3 Vegetation

The Kimberley is a unique bioregion within the Australian Monsoon Tropics biome (Pepper and Keogh, 2014), and extends from the high rainfall tropics in the north, through tropical savanna, to the semi-arid deserts of the south and southeast, punctuated by a variety of other environments including rainforest, mangroves and wetlands (Government of Western Australia, 2011). The

12 Chapter 2

Kimberley itself is divided into seven bioregions including the North Kimberley, Central Kimberley, Victoria Bonaparte, Ord-Victoria Plains, Dampierland, Tanami, and Great Sandy Desert. Of these, some have remained relatively untouched by European influence, with the North Kimberley still containing all native mammal species present at the time of European contact (Government of Western Australia, 2011). These bioregions broadly reflect the underlying geology, with vegetation on the Kimberley Plateau, King Leopold and Halls Creek Orogens (Southern Kimberley Ranges) characterised by tropical savanna woodland of the North and Central Kimberley bioregions (Pepper and Keogh, 2014) (Figure 2.2D). The surrounding bioregions on differing geology (e.g. Victoria Bonaparte, Ord-Victoria Plains, Dampierland, Tanami, and Great Sandy Desert) accordingly have dissimilar vegetation associations (McKenzie et al., 2009). Regardless of these vegetation associations, assemblages on the springs are distinct from the surrounding vegetation, and are often unique to each (Department of Environment and Conservation, 2012).

13 Chapter 2

2.4 Climate

The Kimberley lies within the seasonally dry tropics, with precipitation predominantly derived during the Austral summer (December – March) from the IASM and tropical cyclones. The ITCZ moves south from the Asian high pressure belt (Suppiah, 1992) from late November onwards, drawing moisture from the IPWP to the Kimberley’s north and the surrounding Indian and Pacific Oceans (Taschetto et al., 2011) (Figure 2.4). There is a strong precipitation gradient within the region with average annual rainfall ranging from 1500 mm/yr in coastal parts of the northwest, to less than 350 mm/yr on the southern boundary (Government of Western Australia, 2011) (Figure 2.3). There is low variation in mean annual temperatures which range from 24 – 27 °C (Bureau of Meteorology, 2017).

14 Chapter 2

Figure 2.3. Mean annual rainfall in the Kimberley (1990-2005) (adapted from Department of Water, 2010)

Active (weaker) monsoon periods correspond with a more southerly (northerly) position of the ITCZ and an associated southerly (northerly) location of the monsoon trough (Suppiah, 1992). In general, during active monsoon periods the monsoon trough is located over the Pilbara Heat Low, which separates Trade Winds to the south and westerlies to the north (Figure 2.4), within which the strong monsoonal convection is embedded (McBride, 1987). In addition to the position of the ITCZ, a number of factors can affect the strength of the monsoon such as the MJO which can alter the strength of these westerlies on a time scale of 40 – 60 days (Wheeler et al., 2009). Over 80% of Australian monsoon onset dates are driven by MJO whilst it may also affect the genesis and nature of tropical cyclones (Zhang, 2013). The strength of the MJO itself (and therefore the strength of tropical convection associated with the MJO) can also be bolstered by subtropical cold surges from western Asia which promote deep convection north of Madagascar, amplifying circulation (Wang et al., 2012), and may also have the effect of pushing the ITCZ further south (Suppiah and Wu, 1998).

Furthermore, given that sea surface temperatures (SSTs) are a key influence of convection and the strength of the monsoon, drivers of SST variability such as the El Niño Southern Oscillation

15 Chapter 2

(ENSO) which operates over a 3 – 7 year cycle are also important in driving Australia’s rainfall (Taschetto et al., 2010), particularly in the tropical north during the Austral summer (Risbey et al., 2009). Under normal conditions, ENSO is associated with convection over Indonesia and subsidence over the eastern Pacific (McPhaden, 2004). During El Niño events the subsidence is centred near Australia, disrupting moisture advection and therefore suppressing precipitation over the continent (Jourdain et al., 2013). Whilst the effects of ENSO are currently muted in northwest Australia by comparison to eastern Australia (McBride and Nicholls, 1983; Bureau of Meteorology, 2017), La Niña events can result in increased spring and summer precipitation in the Kimberley, whilst particularly strong El Niño events (e.g. that of 1982 – 1983) can cause significant reductions in the region’s rainfall (Bureau of Meteorology, 2017). The intensity of ENSO phases can also be modulated by the Inter-decadal Pacific Oscillation (IPO) which weakens El Niño and strengthens La Niña events during its positive and negative phases respectively (Power et al., 1999). Interactions between ENSO and the Indian Ocean Dipole (IOD) can also modulate rainfall, whereby concurrent positive IOD phases and El Niño events reduce precipitation (Meyers et al., 2007). However, the IOD has little direct impact on monsoon activity in the Kimberley since IOD events typically occur during the Austral winter and spring (Taschetto et al., 2011). More recently, El Niño Modoki events have been identified as another driver of rainfall variability in the northwest, during which warm SSTs in the central Pacific and anomalously cool SSTs in the west and east (Ashok et al., 2007) result in shorter, yet more intense monsoons due to the anomalous cyclonic circulation which strengthens convection embedded within northwest monsoon flow (Taschetto et al., 2010). The relationship between ENSO and rainfall may change on longer timescales (Webster and Palmer, 1997) due to interactions with other systems such as the IPO and IOD, potentially entrenching El Niño or La Niña states.

16 Chapter 2

Over long timescales such as the late Quaternary, the amount of incoming solar radiation to the Earth varies via changes in the Earth’s axial tilt, wobble, and orbit over different periodicities known as Milankovitch cycles (House, 1995). These include the precessional (19,000 to 23,000 years), obliquity (41,000 years) the eccentricity cycles (100,000 years). Milankovitch insolation variations are known to influence low-latitude monsoon regimes, and the relatively small size of the Australian continent combined with a lack of strong topographic contols (e.g. the Tibetan Plateau which plays a significant role in driving the Indian-East Asian summer monsoon) makes the Australian monsoon perhaps more sensitive to variations in insolation, with ocean-land links promoting strong monsoon flow (Wyrwoll et al., 2007). This sensitivity possibly introduces a degree of “complex” behaviour enabling different combinations of climate forcing mechanisms to contribute to monsoon activity at different times (Marshall and Lynch, 2006).

Spectral analysis on tropical Australian marine pollen and charcoal records demonstrates that long term variations in monsoonal precipitation are coeval with Milankovitch frequencies (Kershaw et al., 2003), whilst proxy climate data from Lake Eyre (Magee et al., 2004), Lynch’s Crater (Kershaw et al., 2007a) and ODP Site 820 (Moss and Kershaw, 2007) also indicate that monsoon activity varies in line with orbital cycles. Additionally, Atmosphere Ocean General Circulation Model sensitivity experiements confirm that tilt and precession exert a significant control on the Australian monsoon system (Wyrwoll et al., 2007; Marshall and Lynch, 2008). This indicates that

17 Chapter 2

Milankovitch cycles play an important role in forcing Australian monsoon activity over the late Quaternary.

2.5 Characteristics of the study sites

The three organic springs analysed in this thesis (Black Springs, Fern Pool, Gap Springs) are located on broadly north-south transect spanning ~100 km between 15.622 – 16.404°S and 126.134 – 126.389°E (Figure 2.5). All three sites are located upon the Kimberley Plateau, and are therefore within the North Kimberley bioregion and fractured rock hydrogeological province. Groundwater outflow to the three springs is consequently from small, variable aquifers with localised and immediate recharge, derived predominantly through outcropping sandstones of the Kimberley Group. The vegetation surrounding the springs is the tropical savanna woodland which characterises the North Kimberley bioregion, predominantly classed as Tropical Eucalypt Woodlands/Grasslands (Major Vegetation Group (MVG) 12) although also some Eucalypt Woodlands (MVG 5), with Eucalypt Open Woodlands (MVG 3), Hummock Grasslands (MVG 20) and Tussock Grasslands (MVG 19) located to the south (Figure 2.5). There are inter-site differences in vegetation at each spring as described below. Due to the strong precipitation gradient in the Kimberley, there are also differences in current climatic conditions at each site. For instance, rainfall data derived from Drysdale River Station (126.38°E, 15.70°S) shows mean annual precipitation in the northern part of the study region to be 1100 mm/yr, by comparison to mean annual precipitation from Mount Elizabeth Station in the southern part of the study region (126.10°E, 16.42°S) which is 1005 mm/yr (Bureau of Meteorology, 2017). There is also a greater temperature range in the southern part of the study region, with data from Doongan Station (126.31°E, 15.38°S) demonstrating a mean annual range of 29.7 – 33.2 °C, whilst Mount Elizabeth Station has a mean annual range of 28.3 – 36.1 °C (Bureau of Meteorology, 2017). Despite these differences across the study region, a common factor is the highly seasonal precipitation regime with (on average) >80 % of precipitation falling during the Austral summer (Bureau of Meteorology, 2017).

18 Chapter 2

Figure 2.5. The location of Black Springs, Fern Pool and Gap Springs in relation to the MVGs and the Kimberley Plateau (the extent of which is depicted by the dashed line)

2.5.1 Black Springs

Black Springs is located the furthest north of the three springs at 15.633°S, 126.389°E and is ~370 m above sea level (Figure 2.12). In this case, groundwater outflow has formed a prominent organic mound spring ~2 m above the surrounding landscape and is listed as a TEC (identifier number 92) (Government of Western Australia, 2014). The mound is covered by a dense monsoon vine thicket with taxa including Pandanus spiralis, Melaleuca viridiflora, Timonius timon, Colocasia sp. and Ficus sp., and surrounded by a fringing swamp with Cyperaceae and Phragmites karka (Department of Environment and Conservation, 2012; field observation) (Figure 2.6). The contrast between the heavily vegetated spring and surrounding Tropical Eucalypt Woodland/Grassland can be seen in Figure 2.7. The spring is located in an area of relatively flat terrain and is in close proximity to the Drysdale River (~4 km).

19 Chapter 2

Figure 2.7. Satellite imagery of Black Springs (Google Earth, 2017). Coring location shown by white cross

20 Chapter 2

2.5.2 Fern Pool

Fern Pool is located at 15.937°S, 126.284°E and is ~450 m above sea level (Figure 2.12), and is comprised of a series of mounds of organic detritus (Figure 2.8A). These mounds are less topographically prominent by comparison to Black Springs (Figure 2.8B), and are less densely vegetated, being predominantly covered by Melaleuca sp., P. spiralis, Typha sp., ground ferns, Cyperaceae, Plectranthus congestus and Ocimum basilicum/Basilicum polystachyon. Upwelling groundwater derived from the localised aquifer could also be seen in the nearby Donkey Creek ~500 m from Fern Pool (Figure 2.8C). The large swamp surrounding the spring vents can be observed in Figure 2.9, and is larger by comparison to Black Springs.

21 Chapter 2

Figure 2.9. Satellite imagery of Fern Pool (Google Earth, 2017). Coring location shown by white cross

2.5.3 Gap Springs

Gap Springs is located the furthest south of the three study sites at 16.404°S, 126.134°E and is ~560 m above sea level (Figure 2.12) and is not topographically protuberant above the surrounding landscape (Figure 2.10). The spring is densely covered by P. spiralis, Melaleuca sp., Banksia dentata and Cyperaceae. The spring is situated in gently undulating terrain and drains northwest into a creek in close proximity (~300 m) (Figure 2.11).

22 Chapter 2

Figure 2.10. The vegetation at Gap Springs is shown in Panels A – C, with the less topographically distinct nature of the spring depicted in Panels A and B

Figure 2.11. Satellite imagery of Gap Springs (Google Earth, 2017). Coring location shown by white cross

23 Chapter 2

Figure 2.12. The location of Black Springs, Fern Pool and Gap Springs in relation to altitude. The extent of the Kimberley Plateau is depicted by the dashed line

2.6 Conclusion

The ancient Kimberley region is geologically varied, with associated diverse hydrogeological, geomorphological and vegetation characteristics. Whilst the climate is dominated by the IASM, there are strong precipitation gradients across the region. There are numerous springs located across the region, both within the fractured rock province and more extensive sedimentary basins, around which organic deposits have accumulated. Sediments such as these are more typically found in lakes and extensive wetlands. Given that the monsoonal climate has resulted in few perennial, extensive water bodies, these organic spring deposits are therefore critical archives of the region’s palaeoenvironment with which to undertake the research within this thesis. The information provided here is therefore essential in understanding individual characteristics at each of the three springs, crucial for providing context for the interpretations made in Chapters 5 – 7.

24 Chapter 3

3 Assessing current knowledge of late Quaternary climate and environmental change in the Kimberley: a synthesis of available records

3.1 Introduction

Palaeoclimate and palaeoenvironmental archives can be used to infer the timing and extent of past changes (Reeves et al., 2013). Understanding such changes during the late Quaternary period, in particular during the LGIT, is important since it was arguably the most significant transition in global climate in the last 100,000 years (Reeves et al., 2013). As outlined in Chapter 1, there is currently limited knowledge of climatic and environmental change in the Kimberley spanning the late Quaternary period. Whilst there is evidence of significant change across northern Australia during the late Quaternary (Reeves et al., 2013), this is predominantly derived from atypical locations such as the Atherton Tablelands (e.g. Dimitriadis and Cranston, 2001; Haberle, 2005; Tibby and Haberle, 2007; Kershaw et al., 2007a; Burrows et al., 2016) and may not be reflective of general conditions across the wider northern Australian region which is predominantly comprised of tropical savanna. Therefore there is a need to develop records from these environments.

As previously described in Chapter 1, the monsoonal nature of the Australian tropics limits the number of perennial water sources and therefore the preservation of robust, continuous, high- resolution sedimentary archives. As a result, there are only a handful of high-resolution records of environmental and climatic change in the Kimberley (e.g. McGowan et al., 2012; Denniston et al., 2013a, 2013b; Proske et al., 2014; Denniston et al., 2015; Proske, 2016), and these are predominantly short, contain hiatuses, or are limited to the wetter coastal regions and as such are primarily concerned with changes in sea level rather than climate and terrestrial environment. In order to accurately identify current gaps in understanding of the Kimberley’s late Quaternary environment and climate, this Chapter reviews all available published data concerning such change in the region spanning the last ~50,000 years, utilising continuous, discontinuous, high-resolution, and low-resolution records. The published records are therefore drawn from a wide-range of disciplines, and include data from relevant offshore (sediment cores, corals, geomorphology) and terrestrial settings (sediment cores, speleothems, geomorphology, archaeological sites).

3.2 Data analysis and interpretation

Metadata for all records discussed in this Chapter is presented in Table 3.1, with locations shown in Figure 3.1. All archive types are discussed individually below in chronological order. A synthesis is presented in Section 3.5. Unless specified, the climatic and environmental inferences discussed below are those made in the original publications.

25 Chapter 3

A number of geochronological methods have been utilised to build chronologies for the records considered in this review, including 14C, 210Pb, luminescence (both optically stimulated luminescence (OSL) and thermoluminescence (TL)), uranium-thorium (U-Th), and oxygen isotope stratigraphy. In most cases, dates are presented in the same format as in the original publication (either yrs BP or cal. yr BP). In order to facilitate a synthesis of all the available records, any records with conventional 14C dates only have been calibrated to calendar years before present (cal. yr BP) using OxCal V4.2.5 (Bronk Ramsey, 2013) and the most recent Southern Hemisphere calibration curve SHCal13 (Hogg et al., 2013) with 0 cal. yr BP representing 1950 A.D. For consistency, all dates will be referred to as “yrs BP”.

For the purposes of this study the late Quaternary event stratigraphy proposed by the Oz- INTIMATE group are adopted (Reeves et al., 2013): The glacial period is considered to span 30,000 – 18,000 yrs before present (BP), including the LGM which is defined as the period between 21,000 –18,000 yrs BP; the deglacial is considered to span 18,000 – 12,000 yrs BP; and the Holocene is considered to begin at 12,000 yrs BP. The Holocene is further split into three classifications: early (12,000 – 8000 yrs BP); mid (8000 – 4000 yrs BP); and late (4000 yrs BP – present). Late Marine Isotope Stage 3 (MIS3) is also considered from ~50,000 – 30,000 yrs BP. Where the following text refers to climatic changes with no specific values, for example “warmer”, “drier”, or “less active monsoon”, these changes are in relation to the previous time period.

26 Chapter 3

Table 3.1. Metadata for late Quaternary palaeoclimate and palaeoenvironmental change in the Kimberley and northwest Australia

Site Name ID Location Publication

Marine records

Sediment cores BRVC 1 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) BHVC1 2 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) BHVC2 3 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) BHVC3 4 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) CWVC1 5 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) CWVC2 6 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) CWVC3 7 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) 8 van der Kaars and De Deckker (2002); van der Kaars Fr10/95 GC17 Cape Range Peninsula et al. (2006) G6-2 9 Argo Abyssal Plain van der Kaars (1991) G6-4 10 Lombok Ridge van der Kaars (1991); Wang et al., (1999) Gb 1 11 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 1 12 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 2 13 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 3 14 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 4 15 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) 16 Yokoyama et al. (2000); Yokoyama et al. (2001a); GC 5 Bonaparte Gulf De Deckker and Yokoyama (2009) GC 6 17 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 7 18 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 8 19 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 9 20 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 10 21 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) GC 11 22 Bonaparte Gulf Yokoyama et al. (2000); Yokoyama et al. (2001a) KH11-1-PC01 23 Bonaparte Gulf Ishiwa et al. (2016) 24 van Andel and Veevers (1967); van Andel et al. LSDH-57 Timor Sea (1967) 25 van Andel and Veevers (1967); van Andel et al. LSDA-149 Timor Sea (1967) 26 van Andel and Veevers (1967); van Andel et al. LSDA-152 Timor Sea (1967) MD01-2378 27 Timor Sea Kuhnt et al. (2015) POVC1 28 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) POVC2 29 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) POVC3 30 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) POVC4 31 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) POVC5 32 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) SO185-18479 33 Timor Sea Kuhnt et al. (2015) SO185-18506 34 Timor Sea Kuhnt et al. (2015) TBVC 1 35 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) TBVC 2 36 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) TBVC 3 37 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) TBVC 4 38 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) TBVC 5 39 Bonaparte Gulf Clarke and Ringis (2000); Clarke et al. (2001) Geomorphology Calcareous nodules 40 Sahul Shelf van Andel et al. (1967) Palaeoshorelines 41 Bonaparte Gulf van Andel and Veevers (1967) Strandline deposits 42 Bonaparte Gulf Clarke and Ringis (2000)

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Corals Adele Reef 43 Northwest Shelf Solihuddin et al. (2016b) Cockatoo Island 44 Buccaneer Archipelago Solihuddin et al. (2015) Irvine/Bathurst Islands 45 Buccaneer Archipelago Solihuddin et al. (2016a) Scott Reef 46 Northwest Shelf Collins et al. (2011) Sunday Island 47 Buccaneer Archipelago Solihuddin et al. (2016a) Tallon Island 48 Buccaneer Archipelago Solihuddin et al. (2016a) Terrestrial records

Sediment cores Black Springs (BSP00) 49 North Kimberley bioregion McGowan et al. (2012) Dragon Tree Soak 50 Great Sandy Desert Wyrwoll et al. (1986); Wyrwoll et al. (1992) King River (KR01) 51 King River region Proske (2016) King River (KR02) 52 King River region Proske (2016); Proske et al. (2014) Mandora Swamp 53 Great Sandy Desert Wyrwoll et al. (1986) Marlgu Billabong/Milligan 54 Parry Lagoons Proske (2016) Lagoon (PL04/05) Speleothems Ball Gown Cave 55 Napier Range Denniston et al. (2013a) Cave KNI-51 56 Ningbing Range Denniston et al. (2013b); Denniston et al. (2015) Geomorphology Cabbage Tree Creek 57 North Kimberley Wende et al. (1997) Cambridge Gulf-Ord 58 North Kimberley Thom et al. (1975) River region Cape St. Lambert 59 Northeast Kimberley Lees et al. (1992) Fitzroy catchment 60 West Kimberley Wyrwoll and Miller (2001) Fitzroy River estuary 61 West Kimberley Jennings (1975); Goudie et al. (1993) Gregory (Mulan) Lakes Wyrwoll and Miller (2001); Bowler et al. (2001); 62 East Kimberley System Veth et al. (2009); Fitzsimmons et al. (2012) Jack’s Waterhole, 63 North Kimberley Fujioka et al. (2014) Durack River King Sound 64 West Kimberley Semeniuk (1981) Victoria Delta 65 Northeast Kimberley Lees (1992a) White Sands 66 North Kimberley Wende et al. (1997) Archaeological sites Wallis (2001); Wallis (2002); Frawley and O’Connor Carpenter’s Gap 1 67 Napier Range (2010); McConnell and O’Connor (1997); Vannieuwenhuyse et al. (2017) Carpenter’s Gap 3 68 Napier Range Vannieuwenhuyse et al. (2017)

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3.3 Marine records

3.3.1 Sediment cores

Several marine cores have been collected from locations adjacent to northwest Australia which contain a range of proxies including pollen, charcoal, elemental carbon, foraminifera, coccoliths, ostracods, radiolaria, bryoza, molluscs, and sedimentary characteristics. Quantitative pollen-climate estimates for this region have also been derived from these marine sediments, spanning the last ~100,000 years (Figure 3.4). Since pollen can be transported offshore via winds and fluvial discharge from adjacent landmasses, the palynological interpretation of marine cores can provide information regarding terrestrial vegetation change (van der Kaars and De Deckker, 2002), despite

29 Chapter 3 often being at lower temporal resolutions than their terrestrial counterparts. The locations of the cores discussed here vary in terms of proximity to the Kimberley coastline, however are interpreted to reflect changes (predominantly or entirely) from this region. For instance, whilst Core G6-2 is located on the Argo Abyssal Plain, some 650km offshore, the direction of ocean currents and wind circulation facilitates pollen flux from the Kimberley (van der Kaars, 1991). Similarly, whilst core G6-4 is located on the Lombok Ridge some 850km northwest of Australia and closer to the Indonesian island of Sumba, the vast majority of pollen deposited in the core is believed to have a northern Australian source (van der Kaars, 1991). Cores were also taken from the Bonaparte Gulf and Timor Sea to the Kimberley’s north in the 1960’s, although it should be noted that chronological uncertainty with these records is high (van Andel and Veevers, 1967; van Andel et al., 1967), however more recent cores from this region are better constrained (De Deckker and Yokoyama, 2009; Wang et al., 1999; Yokoyama et al., 2000; Clarke et al., 2001; Yokoyama et al., 2001a; Kuhnt et al., 2015; Ishiwa et al., 2016).

Abundant arboreal and aquatic terrestrial pollen during late MIS3 suggests conditions at this time were humid, with precipitation predominantly falling during the austral winter (van der Kaars and De Deckker, 2002) and quantitative pollen-climate estimates demonstrating that the climate was also cooler than present (van der Kaars et al., 2006). Increased representation of Casuarina from 54,000 yrs BP indicates a reduction in mean annual precipitation (van der Kaars and De Deckker, 2002), with a decline in arboreal and aquatic taxa concurrent with an increase in sclerophyll herbs after 40,000 yrs BP suggesting continued weakening of the monsoon from this time (van der Kaars, 1991; van der Kaars and De Deckker, 2002). Drier conditions then appear to have persisted throughout the glacial until the end of the LGM, with an increased abundance of sclerophyll herbs and Callitris from 35,000 yrs BP until ~20,000 yrs BP, and a reduction in pollen concentrations suggestive of more open vegetation (van der Kaars and De Deckker, 2002). Quantitative pollen- climate estimates suggest that during the LGM the summer monsoon was virtually absent in northwest Australia (van der Kaars et al., 2006), whilst significant fluctuations are seen in the pollen taxa alongside with low pollen concentrations indicative of a highly variable climate during this time (van der Kaars and De Deckker, 2002). Conditions are inferred to have been particularly arid towards the end of the LGM, with an increase in grass and desert oak (Allocasuarina decaisneana) pollen (currently found growing in Australia’s arid zone) at 18,000 yrs BP (van der Kaars 1991). During the LGM there was a reduction in carbonate content of Timor Sea sediments, reflective of reduced fluvial output from Australia’s northwest as a result of a weakened monsoon (van Andel et al., 1967). A number of shallow sediment cores also suggest that sea levels in the Bonaparte Gulf

30 Chapter 3 during the LGM fell by ~120 m (Yokoyama et al., 2000, 2001a; De Deckker and Yokoyama, 2009; Ishiwa et al., 2016) (Figure 3.2). Dramatic increases in benthic foraminifera and sedimentation rates in the Gulf reflective of shallower water and area-restricted sedimentation, suggesting that what is currently the Bonaparte Depression became marginally marine (van Andel and Veevers, 1967; van Andel et al., 1967). However, no evidence of truly lacustrine conditions have been found for the Bonaparte depression indicating that it became semi-enclosed rather than a “lagoon” (van Andel et al., 1967).

A rapid increase in water depth at the end of the LGM occurred in the Bonaparte Depression at ~19,000 yrs BP (De Deckker and Yokoyama, 2009), with the appearance of planktonic foraminifera and coccoliths between ~18,000 and 16,000 yrs BP also indicative of rising sea levels and greater connectivity between the Bonaparte Depression and Timor Sea (van Andel and Veevers, 1967; van Andel et al., 1967). This sea level rise facilitated an increase in mangrove forests and salt marshes, reflected by increasing abundance of mangrove and salt marsh pollen at this time (van der Kaars, 1991). Pollen data also suggests that the climate fluctuated rapidly throughout the deglacial until approximately 14,000 yrs BP (van der Kaars and De Deckker, 2002).

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Multi-proxy evidence from several marine cores indicates an increase in summer monsoon activity during the latest Pleistocene between ~15,000 and 11,000 yrs BP. For instance, increases in aquatic pollen at the expense of sclerophyll herbs after 14,000 yrs BP suggest wetter conditions from this time onwards (van der Kaars and De Deckker, 2002), whilst quantitative pollen-climate estimates depict enhanced monsoon activity from 15,000 cal. yrs BP (van der Kaars et al., 2006). Geochemical data from the Timor Sea suggests a somewhat later increase in monsoon activity, with enhanced terrigenous flux from northwest Australia from ~13,000 – 11,000 yrs BP (Kuhnt et al., 2015) (Figure 3.3).

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The marine records universally suggest active monsoon conditions during the early-Holocene, with an increase in Eucalyptus pollen indicative of increased woodland cover and an associated rise in mean annual precipitation to at least 500 mm/yr (van der Kaars, 1991). These wetter conditions are inferred to have led to a reduction in biomass burning, reflected by a decline in charcoal abundance (Wang et al., 1999).

Quantitative pollen-climate estimates demonstrate that highest precipitation values occurred between 7000 and 6000 yrs BP (van der Kaars et al., 2006). A reduction in foraminifera in the Timor Sea is also indicative of warmer temperatures during the early-Holocene after ~11,000 yrs BP (van Andel et al., 1967), with quantitative pollen-climate estimates placing peak temperatures at 8000 yrs BP (van der Kaars et al., 2006). An increase in mangrove pollen during the early-Holocene until ~6000 yrs BP suggests that sea levels continued to rise until the mid-Holocene facilitating mangrove forest expansion, also known as the “Big Swamp” phase (van der Kaars and De Deckker, 2002; Clarke et al., 2001). The pollen records then depict a contraction in mangrove forests and an increase in riparian and dryland vegetation, indicative of culmination of the “Big Swamp” phase at approximately 6000 yrs BP (Clarke et al., 2001). They then suggest short term periods of aridity throughout the mid- and late-Holocene centred at 7000 and 5000 yrs BP (van der Kaars and De Deckker, 2002), with quantitative pollen climate-estimates indicating a weakened monsoon commencing at 5000 yrs BP (van der Kaars et al., 2006).

3.3.2 Geomorphology

A number of geomorphic indicators recording late Quaternary environmental and climatic change are found adjacent to the Kimberley’s coast including palaeoshorelines, offshore strandlines, and calcareous nodules. It is important to note that the chronologies of several of these records are not well constrained, and that these records can offer only a “snapshot” of conditions prevailing at certain times e.g. a single flooding event, and as such, are discontinuous in nature.

During the glacial, the development of strandline deposits (now drowned) in the Bonaparte Gulf is believed to have been facilitated by sea level “stillstands” or low amplitude fluctuations associated with enhanced aridity (Clarke and Ringis, 2000), whilst the formation of calcareous nodules on the Sahul Shelf at this time can also be attributed to weathering in semi-arid conditions during this period of lower sea levels (van Andel et al., 1967). Rising sea levels throughout the deglacial and into the early-Holocene resulted in the preservation of a number of palaeoshorelines (dated at 9000 yrs BP) in the Bonaparte Gulf (van Andel and Veevers, 1967).

3.3.3 Corals

Living and fossil corals can provide information on seasonal, decadal and centennial climatic variations, based on proxies such as Sr/Ca ratios and δ18O values. Whilst no such records currently exist for the Kimberley, the growth history of several reefs along the Kimberley coastline provide evidence for changing sea level in northwest Australia (Figure 3.5).

During the early-Holocene, a phase of coral building was recorded at Scott Reef at 11,500 yrs BP which corresponds with Meltwater Pulse 1B during a period of post-Younger Dryas warming (Collins et al., 2011). Reef growth in the Buccaneer Archipelago was initiated somewhat later, with coral building from 9000 yrs BP at Cockatoo Island (Solihuddin et al., 2015) and at ~7300 – 7200 yrs BP at East Tallon Island, suggesting that coral accretion occurred shortly after Holocene sea- level rise flooded the continental shelf over an older Pleistocene reef surface (Solihuddin et al., 2016a). The discrepancy in these initiation dates from within the same archipelago is attributed to more favourable early-Holocene environmental and oceanographic conditions for coral accretion in the more southerly reefs (Solihuddin et al., 2016a).

A sustained period of reef growth at both Cockatoo Island and Scott Reef continues to track moderate rates of sea level rise until ~7000 to 6500 yrs BP until sea level stabilised in the mid- Holocene, after which coral accretion slowed (Collins et al., 2011; Solihuddin et al., 2015). Adele Reef also demonstrates rapid early-Holocene accretion until at least ~5000 yrs BP (Solihuddin et al., 2016b). Reef accretion generally slowed in the mid-late-Holocene, with dates from Tallon

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Island suggesting growth culminated between ~5000 and 4000 yrs BP (Solihuddin et al., 2016a), whilst dates from Adele Reef, further offshore, suggest this reef platform reached sea level at ~3000 yrs BP (Solihuddin et al., 2016b).

Figure 3.5. Coral growth records at Cockatoo Island (Solihuddin et al., 2015) and Scott Reef (Collins et al., 2011) (adapted from Solihuddin et al., 2015)

3.4 Terrestrial records

3.4.1 Sediment cores

There are a handful of terrestrial sediment cores in the Kimberley which provide evidence for environmental and climatic change in northwest Australia, incorporating proxies such as pollen, charcoal, foraminifera, dust, and sedimentary characteristics. Of these records, only two are believed to be continuous (Wyrwoll et al., 1986, 1992; McGowan et al., 2012) (Figure 3.6), however of these two cores, Dragon Tree Soak contains stratigraphic information only (Wyrwoll et al., 1986). Ultimately, none of the terrestrial sediment cores extend past the early-Holocene (prior to 9000 yrs BP) (Figure 3.6) and as such, these records are only able to provide evidence of changes from 9000 yrs BP to present. 35 Chapter 3

Figure 3.6. Terrestrial sediment cores recovered in the Kimberley. The length of the records are depicted by grey bars, with white bars indicating hiatuses

In the early-Holocene a pollen record from the King River region indicates that extensive mangrove forests were established by 9000 yrs BP (Proske et al., 2014). This has been attributed to the “Big Swamp” phase, believed to have been facilitated by rising sea levels, warming climate, and increased monsoonal precipitation (Proske et al., 2014). The presence of marine foraminifera in these terrestrial sediments at ~7500 yrs BP are further suggestive of rising sea levels and open marine conditions (Proske et al., 2014).

Increases in back mangrove taxa and declines in Aegiceras corniculatum in the King River region at ~7400 yrs BP are suggestive of sea-level stabilisation (Proske et al., 2014), with the humid conditions characteristics of the early-Holocene interpreted as having persisted until the mid- Holocene. For instance, the expansion of woodland and savanna taxa dependent on soil moisture until ~6500 yrs BP (e.g. Cochlospermum) is indicative of a more active summer monsoon, concurrent with higher sedimentation rates and increasing grain size also suggestive of enhanced moisture availability between ~8400 and 7400 yrs BP (Proske et al., 2014; Proske, 2016). These wetter conditions are reflected by an increasing abundance of perennial aquatics (e.g. Cycnogeton dubium) in the Kimberley’s northwest at ~6000 yrs BP (McGowan et al., 2012).

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Whilst initiation of organic sediment accumulation by at least ~7200 yrs BP at Dragon Tree Soak has been interpreted by the authors as demonstrating uninterrupted sediment accretion and general climatic/environmental stability since the mid-Holocene (Wyrwoll et al., 1986, 1992), there is limited chronological information for this site other than basal ages and as such it is difficult to conclude whether sedimentation has been continuous or otherwise. In contrast, other sedimentary records from the region depict significant variability throughout this period. For instance, pollen from Kimberley’s northwest suggests that the monsoon became intermittent or weakened at ~5800 yrs BP with a transition to dry swamp environments dominated by Pandanus and declines in aquatic taxa (McGowan et al., 2012). A large increase in the aquatic C. dubium and fluvial sedimentation at ~4500 yrs BP is indicative of a brief return to active monsoon conditions, before low pollen concentrations and decreasing representation of aquatic taxa suggest a weakening monsoon throughout the late-Holocene (McGowan et al., 2012). Particularly arid conditions are recorded in the Kimberley’s northwest between 2800 and 1300 yrs BP, with minimal aquatic taxa and an increase in the deposition of long-travelled aeolian dusts from the eastern Simpson Desert and Lake Eyre Basin (McGowan et al., 2012). This broadly corresponds with a decrease in permanent freshwater features in the King River region (Proske, 2016). Finally, increases in perennial aquatic pollen and charcoal concentrations in the northwest from 1300 cal. yrs BP (McGowan et al., 2012), and the presence of seasonally wet floodplains at Parry Lagoons from at least 600 yrs BP (Proske, 2016), indicate ameliorating conditions sometime in the last millennium, with reliable monsoon rains and increased biomass burning.

3.4.2 Speleothems

Two speleothem records are available from the Kimberley: Ball Gown Cave in the Napier Range (Denniston et al., 2013a); and Cave KNI-51 in the Ningbing Range (Denniston et al., 2013b, 2015). These records utilise both stable isotopes (δ18O) (Denniston et al., 2013a, 2013b) and mud layers (Denniston et al., 2015) as proxies for IASM strength, and tropical cyclones. These records are of a high temporal resolution and are semi-continuous (containing hiatuses), with the Cave KNI-51 δ18O record spanning the last ~9000 years (Denniston et al., 2013b), the mud-layer record from the same cave spanning the last ~2000 years (Denniston et al., 2015), and the Ball Gown Cave δ18O record ranging from ~8000 to 40,000 yrs BP (Denniston et al., 2013a) (Figure 3.7). In tropical regions such as the Kimberley, δ18O is primarily thought to be influenced by precipitation rather than temperature (Dansgaard, 1964), whilst mud layers incorporated in speleothems are believed to be a result of cave flooding during extreme rainfall events. As such these stalagmites provide a record of past changes in the Kimberley’s climate.

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Between ~38,000 and 31,000 yrs BP increases of between 2 - 3% in δ18O values occur during Dansgard-Oeschger (D/O) events 5-8, suggestive of weaker monsoon activity at these times (Denniston et al., 2013a). In general throughout the LGM δ18O values indicate that the monsoon appeared to be variable but moderately active.

During the deglacial between ~16,000 and 13,000 yrs BP, δ18O values suggest that the monsoon strengthened, weakened and then strengthened once more. These millennial-scale changes correspond with Heinrich Event 1 (H1), the Bølling-Allerød (B/A) and the Younger Dryas (H0), and are interpreted as the result of forcing of the IASM by Northern Hemisphere climatic changes (Denniston et al., 2013a). Ultimately, there is an overall trend of increasing monsoon activity from the latest Pleistocene after ~15,000 yrs BP into the early-Holocene (Figure 3.7).

During the early-Holocene δ18O values depict active monsoon conditions, particularly between 9000 and 7000 yrs BP (Denniston et al., 2013b). Throughout the mid-Holocene the monsoon remained active, albeit weakened somewhat between 7000 and 5500 yrs BP, followed by a return to active monsoon conditions from 5000 - 4000 yrs BP (Denniston et al., 2013b). However, the transition into the late-Holocene is marked by a dramatic decrease in δ18O values and a change in mineral phase from calcite to aragonite indicative of significant weakening of the IASM, with peak

38 Chapter 3 aridity centred at 1500 – 1200 yrs BP (Denniston et al., 2013b). This period of decreased monsoon activity broadly corresponds with a decrease in the number of extreme rainfall events primarily due to tropical cyclones experienced at the site between 1450 and 1100 yrs BP, although there were a large number of extreme rainfall events immediately prior to this arid phase between 1900 and 1550 yrs BP (Denniston et al., 2015). This aridity is followed by ameliorating, but slightly variable conditions throughout the last millennium (Denniston et al., 2013b). Within the last 1000 years, extreme rainfall events increased until 500 yrs BP, decreased until 300 yrs BP and then increased in the last 200 years (Denniston et al., 2015).

3.4.3 Geomorphology

Within the Kimberley evidence of late Quaternary climate and environmental change is also preserved in geomorphological archives. These include palaeoshorelines, chenier sequences, dunes, flood-flipped boulders, and estuarine, lacustrine and alluvial deposits (e.g. Figure 3.8). Their presence, absence, or variability in this region is predominantly reflective of changes in water availability in the landscape, which in the Kimberley is primarily indicative of changes in monsoon activity. Since geomorphological features can be dated they can therefore provide a record of these climatic changes, however, similar to marine geological records these terrestrial geomorphological records can only offer a “snapshot” of prevailing conditions (e.g. one flooding event) and are temporally discontinuous (see Section 3.3.2). Furthermore, caution must be exercised with several of these records since their chronologies are not well defined (e.g. Jennings, 1975; Thom et al., 1975; Bowler, et al., 2001; Wyrwoll and Miller, 2001).

During MIS3, dates from longitudinal dunes in the Gregory (Mulan) Lakes System in the Kimberley’s east demonstrate a period of increased dune building and pedogenesis until ~51,000 yrs BP, indicative of relatively dry conditions (Bowler et al., 2001). More active monsoon conditions then appear to prevail over the next ~13,000 years, with coarse gravels and lacustrine sediments deposited in the Gregory Lakes basin between ~50,000 and 37,000 yrs BP indicative of higher lake levels (Veth et al., 2009; Fitzsimmons et al., 2012). This corresponds with deposition of alluvium at Cabbage Tree Creek in the Kimberley’s north at ~37,000 yrs BP, suggestive of enhanced fluvial activity (Wende et al., 1997). This is followed by intermittent dune activity from ~35,000 during drier conditions (Fitzsimmons et al., 2012) and a weakening monsoon during the transition into the glacial period.

Geomorphological evidence suggests that there was increased aeolian activity during the LGM and that the monsoon was weak. For instance, palaeosols indicative of drier conditions, whilst not directly dated, are buried under post-LGM sediments in the Gregory Lakes basin (Wyrwoll and 39 Chapter 3

Miller, 2001), and there is evidence of intermittent dune building in the Gregory Lakes basin at this time (Fitzsimmons et al., 2012). These changes correspond to a period of elevated activity at a climbing dune in the Kimberley’s north (Wende et al., 1997). Towards the end of the LGM heightened aridity is suggested by linear dune emplacement in the Fitzroy River estuary (Goudie et al., 1993).

During the deglacial intermittent dune building continued in the Gregory Lakes basin until ~12,000 yrs BP (Fitzsimmons et al., 2012), whilst a short period of dune activity in the Gregory Lakes basin at ~11,500 yrs BP may suggest either increased aridity, or enhanced fluvial sediment supply from Parnkupirti Creek under an increased discharge regime (Fitzsimmons et al., 2012). However, lacustrine deposits at higher than modern lake levels suggest a more active monsoon commencing earlier at 14,000 yrs BP (Wyrwoll and Miller, 2001). Active monsoon conditions then appear to continue into the early- and mid-Holocene, with alluvial deposits in the Fitzroy catchment (Wyrwoll and Miller, 2001) and along Cabbage Tree Creek between 12,000 and ~5000 yrs BP indicative of increased fluvial activity (Wende et al., 1997). In addition, boulder-flip ages from the Durack River are suggestive of extreme floods in the early- and mid-Holocene at 10,300 ± 1900 and 5600 ± 1000 yrs BP (Fujioka et al., 2014). Evidence of the early to mid-Holocene “Big Swamp” phase is recorded in the deposition of mangrove clays in the Fitzroy Estuary, and organic muds and mangrove woods in the Cambridge Gulf-Ord River region between 10,400 yrs BP and 5500 yrs BP. (Jennings, 1975; Thom et al., 1975).

The active monsoon conditions and “Big Swamp” phase of the early- to mid-Holocene were followed by a short lived period of sand mobilisation and dune-building in the Gregory Lakes basin at ~5000 yrs BP, suggesting aridity (Fitzsimmons et al., 2012). Elsewhere, tidal flats in King Sound ceased prograding at ~5000 yrs BP and have been eroding since, indicating that sea level stabilised around this time (Semeniuk, 1981). During the late-Holocene the monsoon appears to have weakened and become more variable, with rapid chenier formation on the Victoria Delta between approximately 2000 and 1200 yrs BP possibly as a result of reduced fluvial input to the shelf (Lees, 1992a), and discrete dune building events from 3000 yrs BP to present at Cape St. Lambert (Lees et al., 1992).

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Figure 3.8. The timing of climatic changes from selected geomorphological records in the Kimberley (from Fitzsimmons et al., 2012:476), including: (a) linear dunes in the Gregory Lakes basin (Fitzsimmons et al., 2012); (b) lake and dune records from the Gregory Lakes basin (Bowler et al., 2001); (c) lake highstands at Lake Mulan (Veth et al., 2009); (d) fluvial and lacustrine sediments in the Gregory Lakes basin and Fitzroy River catchment (Wyrwoll and Miller, 2001); and (e) lake and dune records from Lake Woods in the Northern Territory (Bowler et al., 1998)

3.4.4 Archaeological sites

Poor preservation conditions for organics in the monsoonal tropics of the Kimberley, coupled with a general lack of “classic” depositional sites (e.g. perennial lakes, swamps, wetlands) has resulted in the examination of archaeological sites for palaeoenvironmental evidence. For instance, phytoliths, plant macrofossils, wood charcoal, and micromorphological evidence of environmental and climatic changes has been preserved in sediments, mud wasp nests, and bird nests at a number of rock shelters (e.g. McConnell and O’Connor, 1997; Wallis, 2001, 2002; Frawley and O’Connor, 2010; Vannieuwenhuyse et al., 2017).

During the MIS3, plant macrofossils at Carpenter’s Gap 1 suggest that the environment was semi- arid, albeit with sufficient moisture availability to support perennial tropical grasslands and sedge

41 Chapter 3 stands from ~48,000 – 34,000 yrs BP (McConnell and O’Connor, 1997). This corresponds with abundant phytoliths indicative of plants which require permanent water sources from the same region at ~43,600 yrs BP (Wallis, 2001), suggesting the monsoon was active at this time. However, during the transition into the glacial, phytolith assemblages indicate that the climate in the Kimberley’s southwest became cooler, drier, and with greater biomass burning by ~37,000 yrs BP (Wallis, 2001). Plant macrofossils also suggest that the climate cooled significantly between ~34,000 and 29,000 yrs BP facilitating the expansion of tropical grasslands, although with sufficient moisture to maintain deciduous trees (McConnell and O’Connor, 1997).

There are some conflicting interpretations from a number of proxies during the glacial period. For instance, from ~29,000 yrs BP abundant herb macrofossils at Carpenter’s Gap 1 are indicative of weakened monsoon activity and aridity (McConnell and O’Connor, 1997), wood charcoal is indicative of a drying environment (Frawley and O’Connor, 2010), however micromorphology at Carpenter’s Gap 3 suggests humid conditions between 27,000 and 25,000 yrs BP (Vannieuwenhuyse et al., 2017). Furthermore, plant macrofossils are indicative of enhanced aridity during the LGM, with a decline in the representation of taxa with high water requirements (McConnell and O’Connor, 1997) and there is a cessation of sediment accumulation at the same site thought to be driven by a reduction in water availability (Vannieuwenhuyse et al., 2017). However, there is some evidence of wetter conditions during at this time (e.g. sponge spicules, diatoms, and sedge phytoliths) (Wallis, 2001). It is possible that these indicators may have been transported to the site anthropogenically from water sources in close proximity such as the Lennard River (Wallis, 2001), since the wood charcoal record suggests that occupants at Carpenter’s Gap 1 visited this river given that fragments of red river gum found in LGM deposits could only have been derived from the banks of a nearby watercourse (Frawley and O’Connor, 2010).

Sediment accumulation at Carpenters Gap 3 and maximum sediment accumulation Carpenter’s Gap 1 occurred in the deglacial from ~17,000 yrs BP, indicative of ameliorating climatic conditions (Vannieuwenhuyse et al., 2017). The monsoon is then believed to have become more active through the transition into the early-Holocene, with abundant plant macrofossils indicative of sedges, deciduous trees and vine thickets at ~11,300 yrs BP (McConnell and O’Connor, 1997). In the late- Holocene fluctuating patterns in micromorphology at Carpenter’s Gap 1 are indicative of increased variability (Vannieuwenhuyse et al., 2017). Phytoliths and wood charcoal from Carpenter’s Gap 1 then suggest that modern vegetation assemblages became established in the area in at least the last few hundred years (Wallis, 2002; Frawley and O’Connor, 2010).

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3.5 Synthesis of climatic and environmental change in the Kimberley

A summary of the palaeoenvironmental and palaeoclimatic information currently available for the Kimberley is presented in Table 3.2 organised by archive type and in chronological order. As discussed in Section 3.2, the time intervals included are: late MIS3 (~50,000 – 30,000 yrs BP); glacial (30,000 – 18,000 yrs BP) including the LGM (21,000 – 18,000 yrs BP); deglacial (18,000 – 12,000 yrs BP); early-Holocene (12,000 – 8000 yrs BP); mid-Holocene (8000 – 4000 yrs BP); and the late-Holocene (4000 yrs BP – present). A synthesis of these records is presented in Figure 3.9.

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Table 3.2. Summary of all published records in the Kimberley and offshore from late MIS3 to present

Time Marine records Terrestrial records period Sediment cores Geomorphology Corals Sediment cores Speleothems Geomorphology Archaeological records Semi-arid with a moderately Moderately active monsoon active monsoon. Cooler and Moderately active but variable between 50,000 and 37,000 yrs BP, drier with increased biomass Late MIS3 Gradually weakening monsoon. No records No records No records monsoon activity, weakening with enhanced fluvial activity at burning from ~37,000 yrs during D/O events 5 – 8. 37,000 yrs BP. Weakening BP, and cooling between monsoon from ~35,000 yrs BP. ~34,000 and 29,000 yrs BP. Enhanced aridity Some conflicting evidence: Weak/absent monsoon, dry conditions, and lower sea some proxies suggest drier open vegetation. Monsoon virtually absent levels forming Weak monsoon during the LGM conditions, some indicative Moderately active but variable Glacial during LGM with sea levels ~120 m lower strandlines and No records No records with heightened aridity, aeolian of a still-active monsoon. monsoon during the LGM. than present. Bonaparte Depression semi- calcareous activity and dune building. Conflicting evidence may be enclosed. nodules on the due to anthropogenic continental shelf. transport of materials. Rapid increase in sea level from ~19,000 Some conflicting evidence: yrs BP, greater connectivity between Rising sea levels Overall intensification of monsoon intermittent dune building in Bonaparte Depression and Timor Sea. forming from ~15,000 yrs BP, with Gregory Lakes basin suggesting Increasing mangrove forests and salt Increasing monsoon activity Deglacial palaeoshorelines No records No records strengthening, weakening and aridity until ~12,000 – 11,500 yrs marshes due to sea level rise. Monsoon from ~17,000 yrs BP. on the strengthening during H1, the B/A BP, but higher lake levels in the activity increased from ~15,000 -11,000 yrs continental shelf. and H0 respectively. same location suggesting monsoon BP, with enhanced fluvial activity and intensification from 14,000 yrs BP. terrigenous flux offshore. Coral accretion “Big Swamp” phase, Active monsoon conditions with Intensifying monsoon and enhanced fluvial Continued sea corresponding warmer, and wetter climate greater fluvial activity. A possible Early- activity/terrigenous flux. Increase in mean level rise and An active monsoon, particularly with Meltwater established extensive extreme flood at ~10,300 yrs BP. Active monsoon conditions. Holocene annual precipitation to at least 500 mm/yr. formation of from 9000 yrs BP. Pulse 1B sea mangrove forests by at least “Big Swamp” phase from 10,400 Reduced biomass burning. palaeoshorelines. level rise. 9000 yrs BP yrs BP. Rising sea levels until Peak monsoon activity between 7000 and Continued coral ~7400 yrs BP. An active 6000 yrs BP. Peak temperatures centred at Active monsoon conditions/fluvial accretion due to monsoon until at least 8000 yrs BP. Sea level rise until ~6000 yrs Active monsoon, weakening activity and “Big Swamp” phase sea level rise. ~6500 - 6000 yrs BP, BP, facilitating “Big Swamp” phase and somewhat between 7000 and 5500 until 5500 – 5000 yrs BP. A Flooding of the particularly between ~8400 Relatively active monsoon Mid-Holocene extensive mangrove forests. Culmination of No records. yrs BP. A return to active monsoon possible extreme flood at ~5600 continental shelf, and 7400 yrs BP. conditions. sea level rise/”Big Swamp” phase at ~6000 conditions between 5000 and 4000 yrs BP. Weaker monsoon and sea then sea level Weakening monsoon from yrs BP. Short term aridity centred at 7000 yrs BP. level stabilisation from ~5000 yrs stabilisation at ~5800 ys BP. Brief return to yrs BP, with weakening monsoon BP. ~5000 yrs BP. active monsoon conditions commencing at 5000 yrs BP. at ~4500 yrs BP. Weakening monsoon, with peak Weakening monsoon, with aridity centred between 1500 and Increasing climatic particularly arid conditions Weakening and more variable 1200 yrs BP, and a decrease in variability, modern Sea level between 2800 and 1300 yrs monsoon, particularly from 3000 Late-Holocene Weakening monsoon. No records. extreme rainfall events between vegetation assemblages stabilisation. BP. Ameliorating conditions yrs BP with peak aridity centred 1450 and 1100 yrs BP. established in at least the in the last ~1000 years and between 2000 and 1200 yrs BP. Ameliorating but variable last few hundred years. increased biomass burning. conditions in the last ~1000 years.

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During late MIS 3 most available records are indicative of a moderately active but weakening monsoon towards the transition into the glacial. However, there are some discrepancies between records. For instance, marine sediment cores suggest that the monsoon weakened gradually, however speleothem records demonstrate that the climate was in fact more variable with the monsoon becoming less active particularly during D/O events 8 – 5 (39,000, 35,000, 34,000 and 32,500 yrs BP respectively). Furthermore, terrestrial geomorphological indicators suggest that there was enhanced fluvial activity at ~37,000 yrs BP in the Kimberley’s north, whilst evidence from archaeological sites in the Kimberley’s west suggest cooler and drier conditions at this time. This may be due, in part, to the higher temporal resolution of the speleothem records.

During the glacial sea levels in the Bonaparte Gulf and Timor Sea were considerably lower than at present (~120 m), with the Bonaparte Depression becoming semi-enclosed and marginally marine, and features such as strandlines and calcareous nodules forming on the exposed continental shelf. The majority of records suggest that the monsoon was considerably weaker, or even absent during the glacial and particularly during the LGM. Drier conditions are inferred to have resulted in more openly vegetated landscapes, increased aeolian activity, and enhanced dune building. However, there is some conflicting evidence, with the speleothems suggesting that the monsoon was in fact still relatively active (albeit variable) during the LGM, and with some of the archaeological records suggesting continued water availability. However, it is possible that fossils within these archaeological records (e.g. sponge spicules, phytoliths, red river gum wood charcoal) were sourced by people from the banks of the nearest watercourse (e.g. the Lennard River) and carried back to the site.

All available records indicate that sea levels rose rapidly during the deglacial, with evidence from marine sediment cores placing this initial rise at ~19,000 yrs BP. As a result, the Bonaparte Depression became increasingly connected to the Timor Sea, palaeoshorelines formed on the continental shelf, and mangrove forests and saltmarshes expanded. All available records indicate that the monsoon became increasingly active, with warmer and wetter conditions and increased fluvial activity, although the timing of this increase varies between records and location. For instance, some marine sediment cores place this intensification at 15,000 yrs BP, whereas others suggest it occurred later between 13,000 and 11,000 yrs BP. Some geomorphological evidence from the Gregory Lakes basin suggests a timing of 14,000 yrs BP, whereas other evidence from the same location demonstrates aridity at this time and an increase in monsoon activity from ~12,000 – 11,500 yrs BP. Finally, an archaeological record from Carpenter’s Gap 3 indicates this intensification occurred much earlier at 17,000 yrs BP. Higher resolution records such as

45 Chapter 3 speleothems from the Napier Range not only place increasing monsoon activity from ~15,000 yrs BP, but also highlight millennial scale variability corresponding with H1 (strengthening), the B/A (weakening), and H0 (strengthening).

Sea levels continued to rise into, and throughout the early-Holocene, forming palaeoshorelines on the continental shelf and facilitating coral accretion, particularly during Meltwater Pulse 1B at ~11,500 yrs BP. All evidence points towards an active monsoon at this time, with a reduction in biomass burning, mean annual precipitation estimates of at least 500 mm/yr, and increased fluvial activity, with particularly active monsoon conditions from ~9000 yrs BP. Boulder flip ages in the Kimberley’s north also suggest that an extreme flood occurred at ~10,300 yrs BP. These warmer and wetter conditions, when coupled with sea level rise, initiated the “Big Swamp” phase with significant expansion of mangrove forests. Terrestrial sediment cores place this expansion from at least 9000 yrs BP, although geomorphic evidence places this earlier at ~10,400 yrs BP.

In the mid-Holocene, sea levels continued to increase along with coral accretion, although the timing of sea level stabilisation and culmination of the “Big Swamp” phase varies between records. For instance, marine sediment cores indicate this occurred at 6000 yrs BP, corals and terrestrial geomorphology place this slightly later at ~5000 yrs BP, whereas terrestrial sediment cores suggest stabilisation at 7400 yrs BP. Most lines of evidence also point to continued monsoon activity at the start of the mid-Holocene, with quantitative climate estimates suggesting peak activity between 7000 – 6000 yrs BP, and peak temperatures at 8000 yrs BP. However, there is some contradiction between the timings of change in monsoon activity. For instance, marine sediment cores and terrestrial geomorphology suggest a weakening monsoon from 5000 yrs BP and short-term aridity at 7000 yrs BP. Speleothems, however, are indicative of a reduction in monsoon activity between 7000 and 5000 yrs BP. A number of records point to a short-lived intensification in monsoon activity towards the end of the mid-Holocene, including terrestrial sediment cores (at ~4500 yrs BP) and speleothems (5000 – 4000 yrs BP), whereas boulder-flip ages indicate a major flood event at ~5600 yrs BP.

All lines of evidence suggest that the monsoon weakened and became increasingly variable in the late-Holocene. In particular, several records indicate that there was a significantly arid period during the late-Holocene, where it is possible that the monsoon failed. The timing of this arid phase corresponds relatively well across a number of records. For instance, terrestrial sediment cores indicate that this occurred between 2800 – 1300 yrs BP, speleothems place peak aridity between ~1500 – 1100 yrs BP, and terrestrial geomorphic archives demonstrate aridity between 2000 – 1200 yrs BP. The climate then appears to have ameliorated at some time over the last ~1000 years, with

46 Chapter 3 increases in biomass burning and the establishment of modern vegetation assemblages. Some variability appears to persist within the last 1000 years, with speleothems indicating multi- centennial scale fluctuations in extreme rainfall events.

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3.6 Conclusion: gaps in the current state of knowledge and future research

This synthesis represents the current state of knowledge regarding climatic and environmental change in the Kimberley over the last ~50,000 years, from late MIS 3 to present. Whilst there are a large number of records in the Kimberley and offshore (Table 3.1), the vast majority of these are of a low-temporal resolution (e.g. marine sediment cores, archaeological sites), discontinuous (e.g. geomorphology), contain information limited to sea level change (e.g. corals, marine geomorphology), or have poorly constrained chronologies (e.g. older publications). Furthermore, whilst marine sediment cores are assumed to reflect terrestrial changes this may not always be the case, as the pollen representation may reflect transport mechanisms rather than the terrestrial environmental setting (Moss et al., 2005).

In compiling the available data, significant gaps in current knowledge have been identified. For instance, there is conflicting evidence between records during late MIS 3 and the glacial, including the LGM. There are also discrepancies in the timings of several key changes, including deglacial monsoon intensification, the period of peak monsoon activity in the early-Holocene, and weakening monsoon strength during the mid-Holocene. Some records also indicate variability whereas others do not (e.g. deglacial millennial scale variability in monsoon strength, and late-Holocene multi- centennial scale variability in extreme rainfall events). Some of these discrepancies could be ascribed to regional variability across the Kimberley, whilst some may be attributed to human activity (e.g. anthropogenic transportation of “moisture” indicative fossils), although without further research these contradictions cannot be resolved.

Developing a comprehensive understanding of past climate and environmental dynamics in this region of the Australian tropics therefore requires high-resolution, continuous records with robust chronologies (Denniston et al., 2013b). However, as described in Chapter 1 and Section 3.1 there are a limited number of high-resolution records in the Kimberley (e.g. terrestrial sediment cores and speleothems), and all those that do exist either contain hiatuses (e.g. Denniston et al., 2013a; Proske et al., 2014; Proske, 2016), are particularly short (e.g. Denniston et al., 2015), or do not extend past the Holocene (e.g. McGowan et al., 2012; Denniston et al., 2013a). It is therefore imperative that new, high-resolution, continuous records with precise chronological control are developed for the Kimberley that extend into (at least) the deglacial. As a result this thesis develops three new, high- resolution records spanning the past ~14,500 years, presented in Chapters 5 and 7.

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4 The Kimberley’s human history: evidence of human and environmental/ climatic interactions during the late Quaternary

4.1 Introduction

As described in Chapters 1 and 3 there are, to date, few records of palaeoenvironmental and palaeoclimatic change in the Kimberley region. Whilst this thesis aims to build new records of change from springs in order to address this, valuable information regarding human-environment interactions can also be derived from the Kimberley’s human history. There is evidence for the arrival of humans in the Kimberley ~44,000 – 49,000 years ago (Hiscock et al., 2016), leaving a rich archaeological legacy alongside one of the world’s most significant and complex collections of rock art. Sources of palaeoclimate and environmental information over the late Quaternary can potentially be derived from the region’s rock art, Aboriginal mythology, and the archaeological record. As such, this Chapter reviews the available literature to describe population densities, occupation patterns, mythology, and stylistic changes in the Kimberley’s rock art from the late Quaternary through to present day, to reconstruct human-environment interactions and the impact of climatic variability and change in the region spanning this period.

4.2 Human arrival in the Kimberley and occupation trends

The landmass of Sahul, the Pleistocene continent of Australia and New Guinea, was first settled by people arriving from South East Asia by watercraft (O’Connell and Allen, 2015). Until recently, human arrival was believed to have been at approximately 47,000 yrs BP with rapid dispersal across the continent after proposed initial landfall in the northwest (O’Connell and Allen, 2015). However recent discoveries at Madjabebe in the Northern Territory show human occupation of northern Australia as early as 65,000 yrs BP (Clarkson et al., 2017), whilst findings from Barrow Island located on the North-West Shelf show dates for occupation between ~46,200 – 51,100 yrs BP (Veth et al., 2017b). At present, archaeological evidence suggests that parts of the Kimberley were occupied from at ~43,000 – 49,000 yrs BP. For instance, excavations at Riwi in the south- central Kimberley reveal hearths dated at ~43,000 yrs BP (Balme, 2000), whilst the world’s earliest ground-edge axe was recovered from Carpenters Gap 1 and dated at ~44,000 – 49,000 yrs BP (Hiscock et al., 2016).

Carbon-14 data can be used as an indicator of population size, e.g. with an increased frequency of dates representing increased population size/human activity. Using this approach, Williams (2013) compiled >5000 14C dates from rock shelters and open sites as a proxy for population densities in Australia over the last 50,000 years (Figure 4.1 depicts available 14C dates specifically for the

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Kimberley after O’Connor and Veth, 2006). Dates indicate that occupation remained at relatively low levels until the LGM, which was perhaps the most significant climatic event faced by humans since their arrival in Australia, and between ~21,000 – 18,000 yrs BP populations appeared to decline by ~60 % (Williams, 2013).

In the Kimberley there is evidence for sparse occupation at Carpenters Gap 1 during and following the LGM (McConnell and O’Connor 1997), whilst evidence for occupation during the LGM at Carpenters Gap 3 is more frequent than for Carpenters Gap 1, probably due to the proximity of the former to the Lennard River (O’Connor and Veth, 2006; O’Connor et al., 2014). Towards the coast, on the Mitchell Plateau and in the Drysdale River region, however, a summary of 14C dates from nine rock shelters (Koolan 2, High Cliffy, Widingarri 1 and 2, Ngurini, Bangorono, Wundalal, and Drysdale 2 and 3) indicate little evidence for occupation between ~22,000 – 12,000 yrs BP (O’Connor and Veth, 2006; see Figure 4.2 for locations of all Kimberley archaeological sites mentioned in the text). Additionally, at Riwi, on the margins of the Western Desert, there is a cessation in sediment deposition between ~30,000 – 5000 yrs BP suggesting that it also remained unoccupied during the LGM and for some time after (Balme, 2000). In general, archaeological records between the sites are often very different, indicating that occupation of certain shelters was opportunistic (e.g. Vannieuwenhuyse et al., 2017).

During the late Pleistocene and into the Holocene (~12,000 yrs BP) population densities across Australia increased, particularly from the late-Holocene at ~4000 yrs BP (Williams, 2013). In the Kimberley there is evidence of increased occupation throughout the mid-late-Holocene at Carpenters Gap 3 and Riwi (Balme, 2000; O’Connor et al., 2014).

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Figure 4.1. A) Plot of all archaeological 14C dates for the Kimberley and B) frequency of dates (Veth et al., 2017a:5)

Figure 4.2. Map showing the location of archaeological sites in the Kimberley discussed in the text

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4.3 The Kimberley’s rock art

The Kimberley’s rock art sequence is thought to be amongst the largest, longest and most complex of any collection in the world, with the region containing tens of thousands of rock art sites (Walsh, 2000; Welch, 2016). Rock art remains central to cultural beliefs of the region’s indigenous populations (Ross et al., 2016) with art still produced in the area today (Chalarimeri, 2001; Blundell and Wollagoodja, 2005; O’Connor et al., 2013; Akerman, 2014). Much of the art is located in rock shelters which are ideal locations for painting preservation, since the majority of art-bearing rock shelter substrates are comprised of hard, stable KLS (Schmidt and Williams, 2008) or sandstone from the Warton unit (Green et al., 2017).

Six major rock art periods were initially classified by Walsh (1994, 2000), the sequence of which is based upon a number of parameters including superimpositions, motif associations and archaeological results (Veth et al., 2017a). This sequence reflects change in both the cultural and natural environment (Aubert, 2012). These six periods are (from earliest to latest) Pecked Cupule, Irregular Infill animal, Gwion (Bradshaw), Static Polychrome (Clothes Peg Figure), Painted Hand (Clawed Hand), and Wanjina. The sequence of these periods, groups and sub-groups is depicted in Figure 4.3, whilst characterisation of the iconography of each period and proposed dating range is outlined in Figure 4.4. It should be noted that terminology for each period is subtly different between the sequences proposed by Walsh (1994) and Veth et al. (2017a). Alternative names have therefore been incorporated into Figure 4.4, and for the purposes of this work the naming convention adopted by Veth et al. (2017a) will be used. More recently, two additional art forms have been described from the south-central part of the Kimberley: black dry pigment and fine scratch-work (O’Connor et al., 2013). These appear to be either synchronous with or superimposed on Wanjina paintings, and are believed to date predominantly from the period of European contact (O’Connor et al., 2013).

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Figure 4.3 The Kimberley rock art sequence (adapted from Walsh, 1994)

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As a result of the challenges posed by chronological control, the antiquity of the Kimberley’s rock art remains unknown since there are few absolute dates (e.g. Roberts, 1997; Roberts et al., 1997; Watchman 1997; Watchman et al., 1997; Roberts, 2000; Watchman, 2000; Morwood et al., 2010; Ross et al., 2016). This is predominantly due to the sandstone substrate on which the art is primarily found which limits the use of U-series dating techniques on over/under art mineral accretions since there is little secondary calcium carbonate available (Green et al., 2017). Furthermore, the artists preferentially used ochre in their paintings making it difficult to apply typical 14C techniques to the art itself (Green et al., 2017). Alternative dating approaches have been used such as the presence and absence of diagnostic subject matter in the paintings, including stone spear points which were introduced to the Kimberley in the mid-Holocene, dingoes which were present in Australia ~3500 yrs BP, and megafauna such as Thylacinus cynocephalus (Tasmanian tiger) which went extinct at ~3000 yrs BP (e.g. Walsh, 1994; Akerman, 1998, 2009; Akerman and Willing, 2009), however this approach can only provide an estimation of age. Some 14C and OSL dates have been obtained on mud wasp nests overlying art (e.g. Roberts et al., 1997; Ross et al., 2016), however those dates that do exist are few and often controversial, and therefore uncertainty remains over the maximum age of the art and age brackets for each major stylistic group.

In order to resolve these questions, an extensive rock art dating campaign supported by four major Australian Research Council projects is currently underway (see Veth et al., 2017a for a summary). This campaign includes a number of different approaches to bracket art ages including: accelerator mass spectrometry (AMS) 14C dating of organics found in pigments, oxalate-rich minerals, and mud wasp nests; U-series dating of sulfate, oxalate and phosphate-rich mineral accretions such as polychrome fringes, dispersed wall coatings, floor glazes, silica stalagmites and skins (e.g. Green et al., 2017); cosmogenic radionuclide dating of boulder scars; and characterisation of microbiological communities and mineral halo growth rates.

Until recently a Pleistocene age for rock art production remained controversial. For instance, OSL methods applied to quartz grains from a mud wasp nest said to overlie a painting returned ages of <17,000 yrs BP (Roberts et al., 1997), however there is doubt over this age due to the positioning of the nest (Aubert, 2012). Uncertainty has also been expressed over descriptions of Pleistocene “megafauna” in the art (Aubert, 2012). Finally, a rock slab sprayed with red ochre was recovered in the Southern Kimberley from excavations dated to a minimum age of ~41,000 yrs BP (O’Connor and Fankhauser, 2001), although this may not be representative of art since ochre can occur naturally in the geological record (Aubert, 2012). However, minimum age estimates of ~16,000 yrs BP derived by OSL techniques on mud-wasp nests over-art (Ross et al., 2016), and new assays

55 Chapter 4 emerging from the four ARC projects (Green, 2016) give the first compelling evidence of a Pleistocene age of Kimberley art production. Whilst these projects are ongoing, Ouzman et al. (2017) propose an “intermediate” chronology for the rock art based on a synthesis of stylistic changes, archaeological and environmental data (shown in Figure 4.4), with this chronology providing age brackets for each major stylistic group. For instance, this “intermediate” chronology suggests that the Wanjina period spans 5000 yrs BP to present (Veth et al., 2017a). However, it should be noted that existing 14C dates indicate that many of the “classic” Wanjina figures occur later than this at least after ~1500 yr BP (Morwood et al., 2010). As such, Walsh (1995) suggests that the “classic” Wanjinas date within the last several hundred years rather than thousands of years BP.

4.4 Aboriginal mythology

Traditional Elders have no knowledge of the history, origins and mythology of several of the Kimberley’s art styles (Walsh, 2006), although there is a wealth of knowledge regarding the more recent Wanjina art. The Wanjinas are deities associated with life-giving rains (Walsh, 1995) and today control the monsoon with elements such as heavy rain, lightning, thunder and floods (Bryant et al., 2007). A common theme of mythology running through the linguistic groups associated with Wanjina period art is that of a “Great Flood”. When linked with currently available dates on Wanjina period art (Morwood et al., 2010), this suggests that this “Great Flood” mythology is of relatively recent origin (Walsh, 2006). Walsh (2006) suggests that the association of cultural sites, art, mythology and geomorphology indicates that this traditional mythology is based on a real event, with handed-down accounts originating in a pre-literate society adapting mythological connotations over time (Walsh, 2006). For instance, one legend depicts the Wanjina causing a Great Flood which originated in northern Australia before spreading across the whole continent (Crawford, 1973). Indeed, two regions within the Kimberley (Cape Voltaire and Collier Bay) have been found to show evidence of mega-tsunami activity dated within the believed time frame of Wanjina mythology (Figure 4.5) which can be traced along ~1500 km of coastline, proposed to be linked to the “Great Flood” event (Bryant et al., 2007).

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Figure 4.5. Mega-tsunami chronology in the Kimberley, falling within the believed time frame of Wanjina mythology (adapted from Bryant et al., 2007)

4.5 Discussion

4.5.1 Climatic inferences from rock art iconography, Aboriginal mythology and population densities

The Kimberley’s rock art assemblage can potentially be used as a source of information about the past (Aubert, 2012), including changes in climate and environment, alongside changes in social structure, ideology, economy, culture, and contact with Europeans (e.g. Ross et al., 2016; Veth et al., 2017a). Climatic inferences can be made from the changes in iconography outlined in Figure 4.4, with potential proxies for change including motifs and information exchange behaviours across the Kimberley and to further afield regions. When coupled with the intermediate chronology proposed by Ouzman et al. (2017) outlined in Figure 4.4, these changes can be tentatively anchored in time. A summary of these climatic and environmental interpretations alongside a possible chronology is presented in Table 4.1.

For instance, art styles in wetter periods would be expected to reflect a “closed” information system and increased stylistic heterogeneity, whereas more arid periods would be expected to have stylistically homogeneous art (“open” information systems) across the region (Veth et al., 2017a). Art from the Gwion period in particular (bracketed as spanning 18,000 – 14,000 yrs BP) has a large distribution suggesting more open information exchange and therefore potentially a more arid phase

57 Chapter 4 coinciding with the end of the LGM and terminal Pleistocene (Veth et al., 2017a). A figure group within this period, the Elegant Action Figures, also features abundant hunting scenes with macropods, potentially indicative of more open savanna vegetation at this time (Walsh, 2006) (Figure 4.7), whilst an Irregular Infill Animal period (20,000 – 18,000 yrs BP) painting believed to be of a Greater Bilby (Figure 4.6) may confirm that an arid, bilby-suited environment was present in the Kimberley’s northwest during the LGM (Walsh, 2000). Furthermore, the abandonment of several sites during the LGM, with the exception of those placed favourably near water resources (e.g. Carpenters Gap 3), also suggests that conditions during this time were challenging. In particular, towards the western coast people appear to have abandoned sites at ~19,000 yrs BP suggesting that locally, conditions were at their most extreme towards the end of the LGM (O’Connor and Veth, 2006). Across the continent as a whole, populations appeared to decline by ~60 % (Williams, 2013), again indicative of the challenging conditions faced by humans during this period.

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The art continues to suggest a connection between the Kimberley, Keep River region and western Arnhem Land until ~10,000 yrs BP indicating continued long-distance exchange of information (Veth et al., 2017a). In contrast, Veth et al. (2017a) identify an increase in stylistic heterogeneity in the Painted Hand and Wanjina periods (5000 yrs BP – present), which may be indicative of wetter climatic conditions. Furthermore, plants and animals make up a larger proportion of motifs during these periods, comprising 52% and 69% in Painted Hand and Wanjina respectively, in comparison to just 10% and 11% in the Gwion and Static Polychrome periods (Veth et al., 2017a) (Figure 4.8). Often depicted in Painted Hand iconography are yams which would have required wetter conditions to grow, whilst fish, crocodile and tortoise motifs reappear in the art (Figure 4.9), all suggestive of ameliorating climatic conditions at ~5000 yrs BP.

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Figure 4.8. Kimberley art motifs by period (Veth et al., 2017a:15)

Figure 4.9. A compilation of turtle and fish motifs appearing in Painted Hand period art. Imagery adapted from Walsh (2000) courtesy of Takarakka Nowan Kas Rock Art Archive

Additionally, the Wanjinas are deities associated with life-giving rains, with monsoon symbolism such as lightning common in “classic” Wanjina paintings (Walsh, 1995) (Figure 4.10). When also linked with the “Great Flood” mythology associated with the Wanjina period, this suggests that this period was one of active monsoon conditions, particularly after ~1500 yrs BP which 14C dates suggest most of the “classic’ Wanjina figures occur after (Morwood et al., 2010). This coincides with an increasing anthropogenic signal in the archaeological record (i.e. an increasing number of artefacts) suggestive of more favourable climatic conditions, both in the Kimberley (e.g., Balme,

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2000; O’Connor et al., 2014; Vannieuwenhuyse et al., 2017) and in general across Australia (Williams, 2013) from the mid-late-Holocene.

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Time period (yrs Climate and environment Rock art examples BP)

LGM Aridity suggested by art iconography (the (20,000 – 18,000 Greater Bilby which is adapted to arid yrs BP) environments), abandonment of archaeological sites, and population decline

Deglacial Aridity suggested by open information (18,000 – 14,000 exchange (a large distribution of yrs BP) stylistically homogeneous art) and art iconography (suggestive of open savanna environments, rare depictions of flora and fauna)

Deglacial to early- Continued aridity suggested by open Holocene information exchange (a large distribution (14,000 – 10,000 of stylistically homogeneous art) and art yrs BP) iconography (rare depictions of flora and fauna)

Mid- to late- Ameliorating climatic conditions Holocene demonstrated by closed information (5000 yrs BP and exchange (greater stylistic heterogeneity of the art) and art iconography (increased more recent examples) depictions of flora and fauna, yams, aquatic species)

Late-Holocene Active monsoon conditions suggested by (1500 yrs BP to Wanjina deities, art iconography (monsoon present) symbology), the “Great Flood” mythology, and increasing anthropogenic signals in the archaeological record

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4.5.2 Anthropogenic impacts on the Kimberley’s climate and environment

It is also possible that the Kimberley’s climate and environment was impacted by humans, although the extent of any human-environment interaction remains under debate, particularly with new evidence of earlier human occupation in northern Australia from 65,000 yr BP (Clarkson et al., 2017). For instance, tropical savanna covers a majority of monsoonal northern Australia, an environment in which fire plays a large role (Russell-Smith et al., 2009). Burning-induced vegetation change can also affect climate through land surface–atmospheric feedbacks (e.g. Ward et al., 2012) such as evapotranspiration, albedo and roughness length (Wyrwoll and Notaro, 2014). For example, fire is proposed to have promoted the transition from forest to savanna during the late Miocene (Hoetzel et al., 2013). Fire is a natural ecological process, with evidence that tropical savanna environments in northern Australian have been shaped by lightning-induced fires over long timescales prior to human arrival (Kuleshov et al., 2006), and given that not all peaks in biomass burning across Australia correspond to changes in human activity (Mooney et al., 2011). However, human arrival is argued to have wrought changes in existing fire regimes and, as a result, tropical savanna vegetation (Kershaw, 1986; Bowman, 1998), with indigenous populations using fire as a land management tool over long timescales. Climate modelling experiments indicate that decreased vegetation cover indeed reduces monsoon activity in northern Australia (Wyrwoll and Notaro, 2014) (Figure 4.11), although it is still unclear whether anthropogenic burning was of the intensity and extent required to alter vegetation on a large enough scale. It is at least likely that climate was the driving factor between changes observed in flora and fauna (in particular, megafauna) in the late Pleistocene before population densities increased in the early and mid-Holocene, following which humans potentially had a much greater impact on ecology (O’Connell and Allen, 2015).

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4.6 Conclusion

The Kimberley contains a rich legacy of cultural artefacts and rock art from a long period of occupation dating back ~44,000 – 49,000 years. These can be used as a record for past changes, in particular changes in climate and environment, and can therefore reveal human-environment interactions which may be tied in with interpretations presented in Chapters 5 and 7. For instance, iconography of the art and the frequency of archaeological remains indicate that conditions in the Kimberley were challenging for modern humans during the LGM, and particularly towards the end of the LGM into the terminal Pleistocene when several sites were abandoned. Conditions appear to have become wetter and more favourable for human occupation into the Holocene from around 5000 yrs BP. However, it is important to note that inferences from the art are dependent here upon the “intermediate” chronology proposed by Ouzman et al. (2017) which will be independently tested by the outcomes of the rock art dating campaign currently underway, and therefore the age brackets proposed for each art style remain tentative. Since settlement and mobility would have altered in response to different environmental settings, it appears that patterns of human occupation and art styles correlate with climatic changes. It is also possible that human activity may have altered the climate and environment, particularly in the late Pleistocene after population density increased. However, the extent of these interactions remains under debate.

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5 A late Quaternary record of monsoon variability in the northwest Kimberley, Australia

Chapter 5 is reproduced from the following publication:

Field, E., McGowan, H.A., Moss, P.T., Marx, S.K., 2017. A late Quaternary record of monsoon variability in the northwest Kimberley, Australia. Quaternary International 449, 119 – 135.

Chapter 5 presents the results of pollen, humification and sedimentological analysis from Black Springs (core BSP00) in the northwest Kimberley. This Chapter addresses research objectives 4, 5 and 8 by developing the first palaeoenvironmental record from northwest Australia to encompass the entire Holocene period and possibly extend into the late Pleistocene (~15,000 years), and demonstrates that organic spring deposits in the Kimberley contain proxies amenable to palaeoenvironmental research. This chapter then interprets the palaeoenvironmental record in terms of potential drivers of change since the LGIT.

5.1 Introduction

The climate of Australia's vast Kimberley region is dominated by the IASM, which forms part of a wider climate system, including the IPWP which plays a major role as a global heat source driving planetary scale circulation (Keenan et al., 1989, 2000). Despite a mean annual rainfall of ~1000 mm/yr, high seasonality (>70% of rainfall occurs between January and March) combined with mean annual potential evapotranspiration of ~1900 mm/yr has created a water-limited environment (Bureau of Meteorology, 2017). Consequently, there are few sites that preserve high-resolution, unaltered records of palaeoenvironmental change. Many of the lakes and wetlands in the region are seasonally ephemeral, implying that their records may be compromised by desiccation (e.g. leading to aeolian deflation) during the dry season, and by scouring from heavy monsoonal rains and flooding in the wet season (Head and Fullager, 1992). The majority of the high-resolution palaeoclimate records that do exist from the Kimberley are from caves (e.g. Denniston et al., 2013a, 2013b; 2015) with only a handful of records of corresponding vegetation change (e.g. McConnell and O'Connor, 1997; Wallis, 2001; McGowan et al., 2012; Proske et al., 2014; Proske, 2016). As a result, the late Quaternary environment and climate of the region and Australia's tropical savanna as a whole remains poorly understood (Reeves et al., 2013), as outlined in Chapters 1 and 3.

The Kimberley has a long history of human habitation stretching back ~50,000 years (see Chapter 4) (Balme, 2000; Fifield et al., 2001; Hiscock et al., 2016). Consequently its archaeological history is of great significance, particularly as it contains one of the greatest concentrations of rock art globally (Aubert, 2012). Understanding the late Quaternary climate of the Kimberley is therefore essential for providing context for this unique archaeological record. The late Quaternary is also a

65 Chapter 5 period of significant climatic and environmental change associated with the LGIT. In this study a ~15,000 year record combining pollen, charcoal, humification and LOI data is developed from an organic mound spring, Black Springs in the Kimberley's northwest. This record extends and builds on an existing ~6000 year palaeoenvironmental record from the same site (McGowan et al., 2012). The record presented here documents the first humification and LOI data for Black Springs, and the first humification dataset for the Kimberley. Recently acquired surface pollen samples have also been utilised in this study to assist interpretation of the extended pollen record. This study confirms that, despite the lack of permanent water sources and sediments with good fossil preservation, mound spring peat deposits in the Kimberley are a potentially rich archive of palaeoenvironmental data.

5.1.1 Mound springs and climate proxies

Peat deposits have been shown to be excellent natural archives of environmental change (Chambers et al., 2012). Whilst the majority of these are located in the high latitudes or high altitude environments (Gaiser and Rühland, 2010), peat deposits are found in many climatic zones including drier environments, where they are most typically associated with springs (Boyd and Luly, 2005). An organic mound will only form at a spring where outflow is higher than the rate of evaporation, thereby preventing desiccation and mineralisation and where discharge is sufficiently low to prevent mound erosion (Ponder, 1986). Most commonly mounds are derived from aeolian deposits, precipitated calcium carbonate, or silicates in volcanic provinces (McCarthy et al., 2010). However, mounds comprised of peat will also form where there is sufficient water in otherwise challenging environments (Boyd, 1990a). Examples include those in the Australian arid and tropical zones (e.g. Boyd, 1990b; Boyd and Luly, 2005; McGowan et al., 2012), in the East African arid zone (e.g. Owen et al., 2004) and in South Africa (e.g. Scott, 1982a, 1982b, 1988; Scott and Vogel, 1983; Scott and Nyakale, 2002). Further detail on organic spring deposits in a variety of global settings is provided in Chapter 6.

Organic mound springs are classed as minerotrophic since water is derived largely from artesian aquifers as well as meteoric sources (Barber and Charman, 2005; Backwell et al., 2014). These springs develop with distinct stages of growth, outlined by Ponder (1986). A juvenile spring typically forms in a small depression which infills with runoff-derived alluvium and aeolian sediments, precipitates from groundwater and decomposing vegetation. In these early stages spring discharge is typically vigorous with a pool forming at the vent and outflow channels conveying the water into a wetland or spring “tail”. The presence of a perennial water source enables the establishment of vegetation at the spring, with subsequent decomposition of this vegetation

66 Chapter 5 contributing to mound growth. As time progresses and the peat mound increases in size less alluvial runoff-derived sediment is incorporated into the spring.

When a spring is active the buried peats remain relatively fresh due to anaerobic conditions and/or the waterlogged nature of the site (Backwell et al., 2014) with capillary creep and outward diffusion of water through the mound limiting oxidation (McCarthy et al., 2010). Groundwater outflow and peat wetness is related to meteoric recharge via pressure transmitted through the aquifer regardless of water retention time (McCarthy et al., 2010). Humification, a proxy for bog surface wetness, will reflect changes in outflow which in this environment is assumed to reflect long term patterns (hundreds to thousands of years) in precipitation which drives aquifer recharge. Spring development and morphology can be reflected in both the fossil pollen assemblages (Boyd,1990b) and the changing organic content at the site from which secondary conclusions about climatic conditions can be made given knowledge of modern vegetation distributions in relation to climate (Moss, 2013). Charcoal accumulation can provide insight into local and regional fire activity (Mooney and Tinner, 2011).

This study uses multiple measures of mound spring conditions to produce a robust, high-resolution reconstruction of changes in the strength of the Australian summer monsoon since the LGIT, whilst also providing a record of spring development and morphology. This record will provide context for ongoing archaeological research in the Kimberley and increase current understanding of the region's late Quaternary climate.

5.2 Regional setting

Black Springs (15.633°S; 126.389°E) is a peat mound spring located in the North Kimberley Bioregion (Government of Western Australia, 2011) (Figure 5.1) in the northern portion of the study region (see Section 2.5). The peat mound is fed by freshwater from local aquifers of low to moderate productivity within the Kimberley's fractured rock province, distinct from the highly productive extensive aquifers of the Canning and Bonaparte sedimentary basins to the east and west, respectively (Brodie et al., 1998) (see Section 2.2). The mound stands ~2 m above the surrounding terrain with organic material comprised predominantly from decomposing vegetation that is growing on the mound (for further details regarding vegetation growing both on the spring and in the surrounding savanna, refer to Section 2.5.1).

The spring is located 7.8 km from Drysdale River Station (126.38°E, 15.70°S) where the mean annual precipitation is 1100 mm/yr, and 29.2 km from Doongan Station (126.31°E, 15.38°S) where mean annual temperatures range between 29.7 and 33.2 °C (Bureau of Meteorology, 2017). As

67 Chapter 5 outlined in Section 2.4, precipitation in the Kimberley is dominated by the IASM and tropical cyclones, both of which typically occur during the austral summer between December and March (DJFM) associated with the seasonal southward migration of the ITCZ (Suppiah, 1992).

A number of modern drivers of climate variability affect the strength of the Australian summer monsoon, including the MJO, the IPWP, and variability in SSTs including ENSO and El Niño Modoki events (see Section 2.4 for further details). Over late Quaternary timescales changes in Australian summer monsoon activity is, to an extent, likely to be driven by orbital forcing (see Section 2.4). Over these timescales there is also evidence of change in the frequency and intensity of ENSO which may have impacted monsoon activity. For example, both climate models and palaeo-records indicate that the frequency and/or amplitude of ENSO may have increased from the mid-Holocene (e.g. Shulmeister and Lees, 1995; Moy et al., 2002; Gagan et al., 2004; Conroy et al., 2008; Marx et al., 2009), with a particularly sharp intensification from ~3700 yr BP until at least 2000 yr BP (Donders et al., 2007), before a decline for the period 1500 - 1000 yr BP (Rein et al., 2004; Stott et al., 2004). There is inconsistency between records, however, with some corals from the Pacific contradicting the inferred Holocene changes in ENSO previously described (McGregor and Gagan, 2004; Cobb et al., 2013).

Given the current muted effects of most ENSO events in the Kimberley (see Section 2.4), it is unclear as to what extent past changes in ENSO would have impacted northwest Australia. However, it is worth noting that the relationship between ENSO and precipitation can change through time (e.g. Webster and Palmer, 1997). For instance, as described in Section 2.4 the intensity of ENSO phases (El Niño and La Niña) is modulated by the IPO whereby El Niño (La Niña) is suppressed (enhanced) during its positive (negative) phase (Power et al., 1999). In a similar manner the IOD can influence the effects of ENSO phases on the climate of northern Australia, with concurrent El Niño and positive IOD events leading to an increased probability of below average rainfall (Meyers et al., 2007). Changes in frequency and intensity of both ENSO phases in response to, for example, longer multi-decadal variability in the IPO and interactions with other teleconnections such as the IOD therefore modulate the Australian monsoon. Mechanisms such as these have been proposed for “entrenched” El Niño or La Niña states argued to be driving changes in records obtained by Koutavas et al. (2002) and Stott et al. (2004). Thus ENSO may have impacted this study region more significantly in the past. Denniston et al. (2013b, 2015) suggest that a change in mean state could have created a stronger coherency between ENSO and the monsoon in Australia's northwest since the mid-Holocene albeit with this connection weakening at some stage in the last millennium, whilst the results of complex network analysis by McRobie et al.

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(2015) also raise the possibility of an ENSO teleconnection to northwest Australia in the late- Holocene (from 3000 yr BP).

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5.3 Materials and methods

5.3.1 Sample collection

A 1.68 m peat core was collected from Black Springs (core BSP00) during the dry season in July 2005 using a D-section corer. The core was sub-sampled in the laboratory with an average sample

70 Chapter 5 width of 7 mm. To assess pollen assemblages in various spring micro-habitats and to aid palaeoenvironmental interpretation, five surface samples were collected during the dry season in June 2015. Surface “grab” samples of ~10 g wet weight were taken along a ~150 m transect extending from the highest point of the mound into the surrounding tropical savanna (Figure 5.4).

5.3.2 Chronology

Eleven samples (initially nine pollen concentrate samples followed by two bulk samples in an effort to understand age reversals in the pollen concentrate dates) through the core were dated by AMS 14C dating. Pollen concentrates were separated for dating following Moss (2013). Samples were submitted to the Waikato Radiocarbon Dating Laboratory where they were pre-treated using the AAA method before being graphitised and prepared for AMS 14C measurement. Conventional 14C ages were calibrated to cal. yr BP using OxCal V4.2.4. (Bronk Ramsey, 2013) and SHCal13 (Hogg et al., 2013) with 0 cal. yr BP representing 1950 A.D. A Bayesian age-depth model was constructed for the core using Bacon 2.2 (Blaauw and Christen, 2011).

5.3.3 Pollen and microcharcoal analysis

Pollen analysis was undertaken on 105 down-core samples and 5 surface samples. With the exception of one down-core sample at 20.5 cm all contained pollen. Core samples consisted of 2 cm3 of dried material, while surface samples consisted of 1 cm3 of wet material.

Pollen and micro-charcoal analysis followed Moss (2013), whereby samples were disaggregated using 10% tetrasodium pyrophosphate (Na4P2O7) heated to 100 °C. Disaggregated samples were passed through 180 µm and 8 µm sieves, with the >8 µm retained fraction being treated with 8% potassium hydroxide (KOH) to remove humic acids. Sodium polytungstate (Na6 {H2W12O40}) at a specific gravity of 1.9 was used to separate remaining minerogenic material from the pollen using centrifugation. The remaining organic fraction underwent acetolysis to dissolve excess organic material and stain palynomorphs for easier identification using a 9:1 ratio of acetic anhydride

((CH3CO)2O) and concentrated sulphuric acid (H2SO4) heated to 90 °C. Lycopodium clavatum (an exotic marker spike) was added to each sample to enable calculation of pollen, charcoal and non- pollen palynomorph concentrations (expressed per cm3). Pollen, charcoal and non-pollen palynomorph accumulation rates (expressed per cm3 per year) were calculated using these concentrations and the growth rates presented in Section 5.4.1. Pollen/micro-charcoal samples were mounted in glycerol (C3H8O3) on slides and counted using light microscopy at 400× magnification, with palynomorph identification utilising the Australasian Pollen and Spore Atlas (APSA Members, 2007). The pollen sum consisted of 200 pollen grains (excluding aquatic taxa and pteridophyte

71 Chapter 5 spores), or two completely counted slides. If the 200 grains were encountered in under ten transects, a total of ten transects were counted to capture a good representation of the slide. Counts are expressed as a percentage of the total pollen sum. The charcoal sum used to calculate charcoal concentrations consisted of all black angular pieces of >5 µm counted across three evenly spaced transects.

Fossil pollen data was collated and plotted using Tilia (Grimm, 1991) and TGView software (Grimm, 2004) with identification of zones guided using CONISS (Grimm, 1987). Multivariate statistics were used to identify floristic patterns in both the fossil and modern pollen datasets, and to compare fossil and modern assemblages.

Ordinations were performed using CANOCO 4.54 (ter Braak and Smilauer, 2002) and plotted using CanoDraw 4.13 (ter Braak and Smilauer, 2002) and included the pollen, spore and non pollen palynomorph data. Two samples (at 39 cm and 95.5 cm) were statistical outliers and were excluded from these analyses. Detrended Correspondence Analysis (DCA) with detrending by segments was used to determine whether linear or unimodal analysis was appropriate based on the length of the first axis, and the data subsequently examined using the linear technique Principal Components Analysis (PCA) following ter Braak and Prentice (1988).

5.3.4 Sediment analysis

LOI analysis was performed on 230 contiguous samples with the exception of 2 samples (at 113 cm and 164 cm) where no sample remained following 14C analysis. Samples were dried at 105 °C and weighed, then placed in weighed and prebaked crucibles and combusted at 500 °C, before finally being weighed at room temperature. Weights were then used to calculate the percentage of organic material in each sample following Heiri et al. (2001).

5.3.5 Humification analysis

Peat humification followed the standard alkali-extraction method of Chambers et al. (2011). Measurements were made on 114 alternate samples, with samples consisting of 0.2 g ground and dried material (60 °C). Humic materials were disaggregated from samples through treatment with 8% sodium hydroxide (NaOH) heated at 95 °C. Samples were passed through 11 µm filter paper and diluted to 25%. An aliquot of each sample was measured for % light transmission and absorbance (3 repeats) in 1 cm diameter polystyrene cuvettes on a GBC Cintra UV-vis spectrophotometer stabilised at 540 nm with de-ionised water as zero standard. Percentage transmission values were normalised to LOI following Blackford and Chambers (1993), a step necessary to remove the anomalously high % transmission values produced by the peats of higher

72 Chapter 5 mineral content at the base of the core. This is required since it is likely that the deeper LOI values are predominantly related to mound spring morphology and do not wholly reflect changes in spring surface wetness. Following Burrows et al. (2014), the normalised data was smoothed using a three point moving average in order to reduce artefacts produced by aberrant values, and detrended by applying a fourth order polynomial (residual values plotted) to remove the impact of catotelm decay and to emphasise high frequency shifts.

5.4 Results

5.4.1 Chronology

Carbon-14 results are presented in Table 5.1. The Bayesian age-depth model (Figure 5.3) suggests that the core spans the last ~15,000 years and shows clear shifts in growth rates, although these are partly a function of the discrete radiocarbon sampling methodology and Bayesian model applied. Average growth rates (uncorrected for compaction) are 0.11 mm/year from the base of the core until ~5400 cal. yr BP, subsequently decreasing over much of the late-Holocene (0.07 mm/year) until ~500 cal. yr BP, following which they increase to 0.44 mm/year.

Dates from the top 94.5 cm of the core returned a coherent age/ depth relationship, however age reversals are present throughout the lower section of the core. P. karka is found growing abundantly across Black Springs, a species known to transport modern carbon into deep sediments via its extensive root system (Boyd, 1990b). It is therefore likely that young carbon has been incorporated into the lower stratigraphic units via root growth. Strikingly similar issues with 14C dating are evident at other peat mound springs in both Australia (Boyd, 1990b; Macphail et al., 1999) and South Africa (Scott, 1982b; Scott and Vogel, 1983; van Zinderen Bakker, 1995; Scott et al., 2003; Backwell et al., 2014). Macroscopic analysis by Scott and Vogel (1983) confirmed tiny rootlets were present throughout the sediments from Rietvlei dam, South Africa probably resulting in the age reversals and erroneously young dates encountered. A subsequent effort by Scott and Nyakale (2002) to remove rootlets from 14C sub-samples at Florisbad Spring, South Africa resulted in a tighter chronology suggesting that rootlets are a primary source of dating problems at mound spring sites. A full review of chronological issues pertaining to organic spring deposits is presented in Chapter 6.

Due to the potentially contaminated deeper 14C ages all dates below 94.5 cm have been excluded from the age model giving a maximum constrained age of 9070 cal. yr BP (Figure 5.3). If the age model is extrapolated using the growth rate for the lower section of the core, it suggests a basal age of approximately >15,000 cal. yr BP at 1.66 m. However, all age estimations below 94.5 cm should

73 Chapter 5 be considered with caution given the uncertainties in extrapolation of the age model to deeper sections of the mound. Therefore, this paper treats ages older than 9070 cal. yr BP as approximate. It is also possible that root contamination may have affected the sediments <94.5 cm despite the coherency of the age-depth relationship in this section of the core. Nonetheless, the results presented both here and previously by McGowan et al. (2012) show strong similarities in the timing of environmental change with previously published records for northern Australia giving confidence in the chronology of climatic and environmental change developed here for the entire core. In an effort to test the validity of the age model tie points between the Black Springs fossil record and other records from the region were identified. This method is common where 14C chronologies contain uncertainty (e.g. Scott and Vogel, 1983; Macphail et al., 1999; Moss et al., 2013). Peaks in biomass burning (recorded by fossil charcoal) previously identified in the Australian tropics and centred at 8000 cal. yr BP and 11,500 cal. yr BP, as well as a reduction in biomass burning from ~7500 to 5000 cal. yr BP (Mooney et al., 2011), are recorded in the Black Springs charcoal record at these times (see Figure 5.7). Similarly, increases in grass during the last millennium in some northern Kimberley records (Proske, 2016) and in the Northern Territory (Shulmeister, 1992) are also mirrored in the Black Springs pollen record (see Figure 5.5). Coherence in the timing of these changes between the Black Springs and other palaeoenvironmental records imply the Black Springs age model is broadly accurate.

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Table 5.1. 14C dates and calibrated ages for Core BSP00. Carbon-14 dates incorporated in the age model are shown in bold, italicised text

Uncalibrated 14C Calibrated age (cal. yr Lab code Depth (cm) Fraction dated age BP)* Wk-29127 516 ± 35 22.5 514 ± 8 (100%) Pollen Wk-28374 3455 ± 30 45 3655 ± 43 (100%) Pollen 5424 ± 23 (75%) Wk-29128 4671 ± 32 55 Pollen 5319 ± 8 (25%) 7720 ± 44 (89%) Wk-29129 6938 ± 37 79 Pollen 7779 ± 8 (11%) Wk-28376 8186 ± 35 94.5 9070 ± 56 (100%) Pollen Wk-29130 7081 ± 40 104 7887 ± 51 (100%) Pollen Wk-41825 6151 ± 84 112.7 7017 ± 134 (100%) Bulk peat Wk-28377 5713 ± 30 126.5 6450 ± 42 (100%) Pollen 8273 ± 31 (58%) Wk-29131 7439 ±36 140 Pollen 8197 ± 21 (42%) 7827 ± 38 (82%) Wk-28375 7033 ± 31 152.5 Pollen 7912 ± 10 (18%) 6254 ± 22 (56%) Wk-41826 5437 ± 22 164.3 Bulk peat 6204 ± 18 (44%) *OxCal V.4.2.4 (Bronk Ramsey, 2013), 1σ error

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Figure 5.3. Bayesian age model generated for BSP00. The age model was generated using Bacon 2.2 (Blaauw and Christen, 2011). The blue dots represent the 14C ages

5.4.2 Surface pollen

Table 5.2 lists the 33 taxa identified in the surface samples and their ecological affinities, whilst Figure 5.4 contains summary pollen plots for each sample and a PCA biplot for the dataset. Pollen assemblages in the five surface samples reflected the current immediate vegetation, indicating that pollen dispersal is localised. Sample MP3-5, collected from the tropical savanna surrounding the spring is, unsurprisingly, dominated by Poaceae (56.3%) and has the highest amount of tropical savanna taxa of all surface samples (19.5%). The PCA confirms tropical savanna taxa are closely associated with this sample including Eucalyptus which comprises a majority of the trees in the savanna. Sample MP2-4, collected from the marshy wetland in the spring tail is dominated by wetland taxa (43%) and in particular by the sedge Cyperaceae (33.4% of the total pollen sum). Poaceae pollen is also abundant in this sample (27%), however given that Phragmites is thought to contribute little to pollen grass assemblages (e.g. Haslam, 1972; Kershaw, 1979; Hall, 1989; Hall, 1990) it is likely that the majority of the Poaceae pollen observed in this sample, and indeed the other modern and fossil pollen samples, is derived from the savanna surrounding Black Springs rather than the Phragmites growing in the wetland. The PCA also indicates that Cyperaceae and ferns are closely aligned with this sample. Sample MP0-3, collected from the partially inundated lower slopes of the mound with a water depth of ~5 cm shows a dramatic increase in spring taxa

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(40%), with the PCA confirming that Melaleuca is most closely associated with this sample, probably derived from the abundant M. viridiflora growing on the mound. C. dubium, a perennial aquatic indicative of pools of water, is also most closely associated with this sample which is to be expected given the water depth. Samples D4-2 and MP1-1 located on the peat mound are unsurprisingly dominated by spring taxa (57.3% and 58.2% respectively), in particular MP1-1 which is located in the centre of the mound where the water table is at or near the surface. The PCA reveals that taxa including T. timon, Pandanus, Mallotus, Euphorbia and Ficus are closely allied with sample MP1-1 reflecting the monsoon vine thicket growing on the mound. The non-pollen palynomorph Pseudoschizaea is most abundant in sample D4-2 which was the driest sample (water table 19 cm below surface) and located on the shoulder of the mound. Pseudoschizaea is thought to be an algal cyst with highest abundances in damp soils and springs in particular (Scott, 1992), and is often indicative of desiccation, summer drought, oxidisation and warmer climates with seasonal drying (Carrión and Navarro, 2002), thus peak values in sample D4-2 are to be expected.

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Table 5.2. Some information on pollen taxa encountered in the surface and core samples

Pollen taxon Vegetation/taxonomic Habitat/Environment name/family unit Ericaceae+ Exotic Heathland Podocarpus+ Exotic Evergreen trees Grasses. Includes open dryland grasses and aquatic Poaceae*+ Grass perennial grasses particularly Phragmites karka Shrubs and trees. Includes both dryland genera Eucalyptus Myrtaceae*+ Myrtaceae and Corymbia and wetland genus Melaleuca Monolete fern spores*+ Pteridophytes Ground ferns in moist locations Trilete fern spores*+ Pteridophytes Ground ferns in moist locations Amyema Loranthaceae+ Spring Mistletoe – epiphytic parasite Arecaceae*+ Spring Palms Breynia cernua Shrub common in monsoon forest and vine thicket, favours Spring Euphorbiaceae+ disturbance Elaeocarpus Spring Tropical evergreen trees and shrubs Elaeocarpaceae*+ Euphorbia Spring Rainforest herbs and shrubs Euphorbiaceae*+ Euphorbiaceae+ Spring Rainforest trees, herbs and shrubs Ficus Moraceae*+ Spring Trees and vines common to monsoon forest and rainforest Mallotus Trees common to monsoon forest and rainforest, favours Spring Euphorbiaceae*+ disturbance Pandanus Pandanceae*+ Spring Pachycaulous trees of vine thickets and watercourses Plectranthus congestus Spring Herb and shrub common to monsoon forests Lamiaceae*+ Sapotaceae+ Spring Trees common to monsoon forests and rainforests Timonius timon Small tree common to monsoon forests and rainforests, may Spring Rubiaceae*+ indicate disturbance Acacia Mimosaceae*+ Tropical savanna Dryland trees and shrubs common to open vegetation Acanthaceae+ Tropical savanna Dryland herbs and shrubs Amaranthaceae*+ Tropical savanna Dryland herbs and shrubs Asteraceae Tropical savanna Dryland herbs and shrubs common in open vegetation (Tubuliflorae)*+ Banksia dentata Tropical savanna Dryland tree common near wet areas and on sandy soils Proteaceae* Brassicaceae*+ Tropical savanna Dryland herbs Callitris Cupressaceae*+ Tropical savanna Dryland trees

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Casuarina Tropical savanna Dryland trees Casuarinaceae*+ Codonocarpus cotinifolius Tropical savanna Dryland shrub or tree. Common on sandy/loamy soils. Gyrostemonaceae*+ Dodonaea Sapindaceae*+ Tropical savanna Trees or shrubs common in open woodlands Eremophila Tropical savanna Shrubs and trees, commonly in arid areas Myoporaceae* Gomphrena Tropical savanna Dryland herbs, common on poor soils Amaranthaceae*+ Newcastelia cladotricha Tropical savanna Dryland herb Verbenaceae*+ Plantago Tropical savanna Dryland annual herbs Plantaginaceae*+ Polygonum Tropical savanna Dryland annual herbs Polygonaceae* Proteaceae+ Tropical savanna Dryland trees and shrubs Sapindaceae+ Tropical savanna Dryland trees and shrubs Terminalia Tropical savanna Dryland trees Combretaceae*+ Tribulus Tropical savanna Arid, dryland herbs Zygophyllaceae*+ Verbenaceae*+ Tropical savanna Tropical trees, shrubs and herbs Colocasia esculenta Wetland Rhizomatous perennial herb – partially submerged Araceae+ Cycnogeton dubium Wetland Emergent perennial aquatic herb Juncaginaceae*+ Cyperaceae*+ Wetland Sedges – predominantly aquatic Malvaceae+ Wetland Annual herbs common to creeks and river edges Myriophyllum Wetland Submerged aquatic herbs Haloragaceae*+ Typha Typhaceae*+ Wetland Reeds/aquatic herbs * Identified in surface sample + Identified in down-core sample

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5.4.3 Fossil pollen and microcharcoal

The fossil pollen and charcoal record for Black Springs is presented in Figure 5.5. CONISS aided the identification of eight distinct zones in the fossil pollen record based on cluster analysis, labelled BSP1 to BSP8 (Figure 5.5). These zones are indicated on the summary diagram (Figure 5.7). Table 5.2 lists the 42 taxa encountered in the fossil pollen dataset and their ecological affinities. Where values are discussed below they are averaged for the entire zone unless otherwise specified.

5.4.3.1 BSP8 (166 - 152 cm; inferred age ~15,000 - 14,000 cal. yr BP)

Zone BSP8 is dominated by Poaceae (38%) and Myrtaceous taxa (43%), with very low values for spring vegetation (2%) and pteridophytes. Some tropical savanna taxa are present in this zone, including Acacia and Gomphrena. Whilst the perennial aquatic C. dubium is present (8%) other wetland taxa such as Cyperaceae are not well represented until the upper part of the zone where values rapidly increase from ~3% to 17%. Zone BSP8 has low charcoal and pollen accumulation rates, and the algal cyst Pseudoschizaea is absent.

5.4.3.2 BSP7 (152 - 108 cm; inferred age ~14,000 - ~10,000 cal. yr BP)

The base of this zone is defined by an abrupt increase in spring and wetland taxa, in particular Pandanus and Cyperaceae. Spring taxa account for 8% of this zone whilst wetland taxa increase by 12% to comprise a quarter of the pollen sum. Values for Myrtaceae are high, however Poaceae abundances decrease to 26% and fluctuate more than within the previous zone. Acacia is more prolific in this period than within any of the other zones, with Terminalia also present in several samples. There is a peak in charcoal accumulation rates from 126 to 122 cm (~11,730 - ~11,380 cal. yr BP). Pseudoschizaea is occasionally present.

5.4.3.3 BSP6 (108 - 70 cm; inferred age ~10,000 - 6840 cal. yr BP)

In zone BSP6 a sustained increase in mound spring taxa occurs representing 26% of the total pollen sum in this zone. In particular Pandanus comprises 19% of the total pollen sum. Wetland taxa are abundant (>25%), in particular C. dubium and Cyperaceae, whilst Myrtaceae declined to 17%. Similarly tropical savanna taxa such as Acacia and Terminalia are less common in this zone. Mallotus, present sporadically throughout the core, has a distinct peak in this zone at 95.5 cm (~9150 cal. yr BP), and similarly the dryland herb Plantago has a small peak at 74.5 cm (7320 cal. yr BP). Accumulation rates for pollen and charcoal are low albeit with small increases in charcoal accumulation at 93.5 cm (9070 cal. yr BP) and between 82 and 74 cm (8020 - 7310 cal. yr BP). Pseudoschizaea is present sporadically in low values.

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5.4.3.4 BSP5 (70 - 53 cm; inferred age 6840 - 4940 cal. yr BP)

Tropical savanna taxa such as Terminalia and Asteraceae (Tubuliflorae) are a feature of zone BSP5 with the latter reaching highest values for the record (4% of the pollen sum). Pteridophytes also increase in abundance, with monolete fern spores also increasing in representation from 3% in zone BSP6 to 7% in zone BSP5. Wetland taxa are less common, Cyperaceae in particular experienced large declines, although there is a greater representation of spring taxa. In this zone, C. dubium appears to have an inverse relationship with Pandanus, most noticeable at 66 cm and 53 cm where declines in Pandanus are mirrored by increases in C. dubium. Myrtaceae values decline to ~11% whereas pollen from the vine thicket tree T. timon is more consistently present having been rare in preceding zones. Pseudoschizaea remains rare and charcoal and pollen accumulation rates remain low.

5.4.3.5 BSP4 (53 -38 cm; inferred age 4940 -2620 cal. yr BP)

The base of zone BSP4 is marked by dramatic increases in T. timon and Pseudoschizaea accumulation rates. Two distinct peaks in T. timon book-end the zone (52 - 50 cm: 35 - 54%; 42 - 41 cm: 27 - 22%) and Pseudoschizaea accumulation rates increased rapidly from 50 cm reaching peak values at 39 cm (2680 cal. yr BP). Charcoal and pollen accumulation rates remain low. The herb or small shrub Amaranthaceae increases in abundance at the top of the zone. Values of Poaceae, pteridophytes (primarily monolete fern spores) and Myrtaceae remain similar to zone BSP5, however Terminalia and the aquatic taxa Myriophyllum are more common.

5.4.3.6 BSP3 (38 -23 cm; inferred age 2620 - 550 cal. yr BP)

Poaceae increases slightly throughout to 38%, whilst wetland taxa and T. timon experience sharp declines with the latter virtually absent. C. dubium in particular reaches the lowest values of the entire record and Myriophyllum also becomes less common. Pseudoschizaea accumulation rates decline abruptly following a peak at 37 cm (2420 cal. yr BP). Pteridophytes and Myrtaceae remain at similar levels to zone BSP4, however several tropical savanna tree and herb taxa are present including Amaranthaceae, Callitris, Asteraceae, Dodonaea and Terminalia. Pollen accumulation rates remain low whilst there is a small increase in charcoal accumulation towards the top of the zone.

5.4.3.7 BSP2 (23 - 11.5 cm; inferred age 550 cal. yr BP - 230 cal. yr BP)

Very high charcoal accumulation rates are characteristic of zone BSP2 whilst pollen accumulation is low. Poaceae is abundant at the base (>63%), although decreases up through (to 18%) concurrent with a dramatic increase in C. dubium. Myrtaceous taxa continue to fluctuate at levels similar to the

82 Chapter 5 previous three zones, whilst mound spring and tropical savanna taxa become less abundant. Pandanus is absent between 22.5 and 16.5 cm (530 - 360 cal. yr BP) during the grass-dominated conditions at the base of this zone. An anomalous sample with abundant T. timon (comprising 46% of the total pollen sum) is present at 12.5 cm immediately following a peak in charcoal accumulation. Pseudoschizaea is virtually absent.

5.4.3.8 BSP1 (11.5 - 0 cm; inferred age 230 cal. yr BP - modern)

The uppermost pollen zone is dominated by wetland taxa. C. dubium reaches peak values for the entire record (>71% of the total pollen sum at 5 cm). Poaceae values are lower than in zone BSP2, while Myrtaceae also recorded the lowest values in the core (6%). T. timon and Pseudoschizaea are absent, although other mound spring taxa such as Pandanus are present albeit at lower values (7%). The majority of tropical savanna taxa present throughout the record are also less common with the exception of Terminalia. Charcoal accumulation rates decline, however pollen accumulation rates increase reaching peak values at 5 cm depth.

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5.4.3.9 Comparison of the fossil pollen and surface sample datasets

The PCA biplot shown in Figure 5.6 illustrates the relationship between the assemblages of the modern surface samples and those in the fossil dataset, zoned to aid interpretation. Samples MP3-5 and MP2-4 appear to contain assemblages significantly different to any found in the fossil record. This is likely a result of the surface samples reflecting their immediate vegetation. For instance, grass and tropical savanna taxa dominate sample MP3-5 which was collected from the surrounding savanna, whilst wetland taxa (sedges in particular) dominate sample MP2-4 which was collected from the mound spring wetland. Since the core was taken from the centre of the mound spring, it would appear that during the time period spanned by the fossil record a spring has always been present, and the peat mound has been of a sufficient size to mask the pollen signal from the surrounding savanna and wetland. The pollen assemblages from the surface samples taken from the peat mound itself (MP0-3, MP1-1 and D4-2) resemble those of the fossil record more closely.

The pollen assemblage of surface sample MP0-3, taken from the partially water inundated lower slopes of the mound, contains a pollen assemblage similar to zone BSP7 (~14,000 - 10,000 cal. yr BP) suggesting two possibilities: that the environmental conditions during zone BSP7 were similar to the wet conditions currently seen at MP0-3; and/or that the mound may have been smaller than present bringing the inundated lower slopes closer to the coring site currently located at the top of the mound, making this zone similar floristically to MP0-3. Sample MP1-1, collected at the top of the mound where vegetation is dense and the peat saturated, is moderately similar to the assemblages of zone BSP4 (4940 - 2600 cal. yr BP) and to some samples from zone BSP5 (6840 - 4940 cal. yr BP). Since MP1-1 is taken from the same location as the core, it can be inferred that the mound was at or near its current extent during the mid-Holocene and therefore conditions at the mound spring during the timespan covered by zone BSP4, and perhaps zone BSP5, were similar to the highly productive, saturated conditions currently seen at MP1-1. Surface sample D4-2, collected on the drier shoulder of the mound in the established monsoon vine thicket bears some resemblance to a small number of samples from zone BSP3 (2620 - 550 cal. yr BP). This provides an indication that zone BSP3 contains great variability and that part of the timespan covered by zone BSP3 featured conditions similar to those currently experienced on the spring shoulder.

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Figure 5.6. PCA biplot of the Black Springs fossil and modern pollen data

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5.4.4 Sediment analysis

LOI values are presented in Figure 5.7 and exhibit an overall trend of increasing organic content up- core predominantly driven by growth of the peat mound gradually excluding alluvial sediments. Organic content is low from the base of the core to 137 cm (~13,000 cal. yr BP) above which it increases, in particular above 102 cm (~9600 cal. yr BP). Peak organic content occurs at 47.5 cm (4090 cal. yr BP). Despite a number of fluctuations (in particular at 42 cm or 3340 cal. yr BP) the core organic content remains high until 38 cm (2690 cal. yr BP). Following this there is an abrupt decline in organics persisting until 25 cm (740 cal. yr BP) then a short return to higher values between 33 cm and 27 cm (2036 - 1020 cal. yr BP). The core organic content then increases and remains stable in the uppermost 24 cm of the core. Figure 5.7 indicates that the changing LOI patterns tend to match the boundaries of the eight pollen zones. In summary zone BSP8 features low LOI values, which increase slightly throughout zones BSP7, BSP6 and BSP5, particularly from 102 cm (~9600 cal. yr BP). Zones BSP4 and BSP3 are distinguished by high and low LOI values respectively, whereas the uppermost zones BSP2 and BSP1 feature high, stable LOI values.

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5.4.5 Humification

The Black Springs humification record is presented in both the summary diagram in Figure 5.7 and in Figure 5.8, with higher (lower) values of % transmission interpreted as indicating decreased (increased) humification of the peats and wetter (drier) conditions (Sillasoo et al., 2007). However, it should be noted prior to interpretation that low % transmission values from the base of the record to 102 cm (~9600 cal. yr BP) are a result of the greater mineral content of the peats. This is possibly due to both the peat mound being smaller than at present facilitating in-wash of catchment sediments and/or windblown sediment due to drier conditions. However, oscillations from 102 cm (~9600 cal. yr BP) to present are inferred as representing changes primarily in bog surface wetness at Black Springs. There are large oscillations in the humification record. Wet (dry) shifts have been defined where residuals clearly cross into positive (negative) values and are shown shaded in grey on Figure 5.8, and are summarised in Table 5.3. Five wet and three dry shifts are defined. Residuals indicate peak moisture between 8500 and 7000 cal. yr BP and peak aridity from 2600 to 1300 cal. yr BP. The trend followed by the humification record is similar to the LOI data, and as such, is well correlated with the boundaries of the eight pollen zones.

Table 5.3. Summarised wet and dry shifts observed in the humification record (approximate depths and ages). The wettest and driest period is indicated by bold, italicised text

Climate From (depth - To (depth - cm) From (age - cal. To (age - cal. yr periods cm) yr BP) BP) Wet 4 23 Present 600 Dry 23 27 600 1000 Wet 27 29 1000 1300 Dry 29 39 1300 2600 Wet 39 40 2600 2800 Dry 40 43 2800 3400 Wet 43 51 3400 4700 Wet 53 103 4900 9600

5.5 Discussion

5.5.1 Mound spring morphology and environmental change at Black Springs

5.5.1.1 An increase in monsoon activity from ~14,000 cal. yr BP

During the LGIT Black Springs appears to have been a juvenile spring, with an almost complete absence of spring pollen taxa prior to ~14,000 cal. yr BP. These conditions continued until ~13,000 cal. yr BP with higher minerogenic content of the sediments due to lower organic production at the spring and a greater likelihood of alluvial sediments being incorporated. The presence of the perennial aquatic C. dubium and Cyperaceae at this time also indicates a juvenile spring with a spring wetland.

Increasing organic content from ~13,000 cal. yr BP reveals that the peat mound began to grow slowly during the transition from the late Pleistocene to early-Holocene, with increases in the abundance of wetland taxa and sedges after this time indicating a more sustained spring wetland and outflow. Increased organic growth would have required more abundant vegetation at the spring with its subsequent decomposition contributing organic material to the site. Increases in spring taxa from ~14,000 cal. yr BP indicate that this was the case. Denser vegetation at the spring, in context, is likely to have required an increase in spring discharge and, since outflow is related to meteoric recharge (McCarthy et al., 2010), it can be inferred that precipitation in this region of the Kimberley increased from ~14,000 cal. yr BP. Comparisons with modern pollen assemblages indicate the

90 Chapter 5 presence of a small peat mound and wet conditions similar to those currently characteristic of the spring's lower slopes from ~14,000 cal. yr BP.

Evidence for enhanced monsoon activity in the late Pleistocene is found preserved in other records across tropical Australasia. In the Kimberley these include higher-than-present lacustrine deposits at Lake Gregory at ~14,000 yr BP (Wyrwoll and Miller, 2001), speleothems from Ball Gown Cave showing increased monsoon rainfall from 13,000 cal. yr BP (Denniston et al., 2013a), greater alluvial deposition along Cabbage Tree Creek in the Kimberley's north from 12,000 yr BP (Wende et al., 1997), and an increase in moisture indicative plant macrofossils from 11,500 yr BP (McConnell and O'Connor, 1997). This late Pleistocene shift in monsoon activity is also identified in marine records adjacent to the Kimberley, with elevated deposition of sediments derived from terrestrial runoff suggesting intensification of monsoon activity from 13,000 cal. yr BP (Kuhnt et al., 2015). Offshore pollen records from this time also suggest increases in monsoon rainfall from 14,100 cal. yr BP at the southern extent of the monsoonal zone (van der Kaars and De Deckker, 2002; van der Kaars et al., 2006) and from ~16,000 to 12,000 yr BP from the monsoon affected Timor Sea records (van der Kaars, 1991; Kawamura et al., 2006; Kershaw et al., 2006).

5.5.1.2 An early-Holocene precipitation maximum

In the early-Holocene the peat mound appeared to grow rapidly in size with a dramatic increase in organic content from ~9600 cal. yr BP indicating dense vegetation cover at the spring and the gradual exclusion of sediments deposited by runoff from the surrounding land surface. This increase in vegetation cover is reflected by the increases in spring taxa observed in the fossil record. The rapid growth of the mound would have required a large increase in precipitation, with humification analysis also showing elevated spring surface wetness from ~9600 cal. yr BP and a particularly wet period between 8500 and 7000 cal. yr BP. Taxa suggestive of wetter conditions also increase from this time including Pandanus - a tree common to moist and humid environments such as vine thickets and along watercourses, and the rainforest genus Mallotus which is most abundant at ~9150 cal. yr BP. Wetland taxa also now comprise a large portion of the total pollen sum, in particular the perennial aquatic C. dubium which suggests standing water at the site. Increases in charcoal accumulation rates at 9070 and 8020 cal. yr BP are indicative of greater biomass burning, likely to be a result of higher fuel loads at, and surrounding the spring.

Speleothem records from the southwest and eastern Kimberley also indicate wetter monsoon conditions in the early-Holocene (Denniston et al., 2013a, 2013b), with the Cave KNI-51 record in particular indicating greatest precipitation between ~9000 and 7000 cal. yr BP (Denniston et al., 2013b), matching the Black Springs record presented here. Pollen, mangrove clays, woods and 91 Chapter 5 organic muds from the Kimberley's north suggest extensive mangrove forests were established by 9000 cal. yr BP and were sustained until at least 6000 yr BP, facilitated by increasing sea level, warmer postglacial temperatures and enhanced freshwater input from a more active monsoon (Jennings, 1975; Thom et al., 1975; Proske et al., 2014). Pollen from the region's north also reflects woodland expansion at this time, with the occurrence of taxa dependent on moist soils suggestive of increased moisture (Proske et al., 2014). Quantitative estimates from offshore pollen records also indicate a thermal maximum at 8000 cal. yr BP and peak precipitation between 7000 and 6000 cal. yr BP (van der Kaars et al., 2006).

5.5.1.3 Active and stable monsoon conditions until 5000 cal. yr BP

The similarities between the pollen assemblages from the mid- late-Holocene zone BSP4 (and to some extent zone BSP5) and sample MP1-1 collected at the coring location, currently at the mound's highest point, indicate that Black Springs appears to have reached its modern extent at least by the mid-Holocene. The pollen, LOI and humification data presented here all suggest continued monsoon activity throughout the mid-Holocene until ~5000 cal. yr BP, albeit with reduced precipitation when compared to the early-Holocene. For instance, the humification data identifies a wet phase persisting until 4900 cal. yr BP, although residuals are lower than in the preceding period indicating a slight reduction in surface wetness. The similarities between the fossil pollen assemblages at this time to the modern pollen assemblages of the productive and saturated conditions in the centre of the mound also indicate an active monsoon. There is a clear change in pollen assemblages at 6840 cal. yr BP as a result of the decreasing abundance of wetland taxa (particularly Cyperaceae) and increases in T. timon and ferns. T. timon is presently found growing on the drier slopes of Black Springs suggesting that whilst moist conditions persisted throughout the mid-Holocene, precipitation and spring outflow were lower. Increased representation of dryland taxa such as Terminalia and Asteraceae also suggest that vegetation surrounding the spring was indicative of a drier climate.

Pollen data from marine core FR10/95 at the southern extent of the monsoonal zone also indicates high rainfall values between 7000 and 6000 cal. yr BP (van der Kaars et al., 2006), whilst speleothem records from Cave KNI-51 in the East Kimberley suggest an active but slightly weaker monsoon between 7000 and 5500 cal. yr BP (Denniston et al., 2013b).

5.5.1.4 Increased variability from 5000 cal. yr BP

From 5000 cal. yr BP to present all proxies indicate increased environmental and climatic variability at Black Springs. All point to a short-lived drying phase at ~5000 cal. yr BP where there

92 Chapter 5 is a sharp decrease in humification data and organic content suggesting decreased productivity at the spring, and perhaps increased aeolian sedimentation due to reduced monsoon rainfall. There is a change in the pollen assemblages at this time with clear decreases in taxa indicative of wetter conditions such as Pandanus and Myrtaceae (likely to be Melaleuca) in favour of vine thicket taxa common on the mound's drier slopes such as T. timon. Pollen from the FR10/95 marine core also indicates short term aridity at 5000 cal. yr BP (van der Kaars and De Deckker, 2002; van der Kaars et al., 2006), concurrent with a period of dune building and sand mobilisation in the Gregory Lakes basin (Fitzsimmons et al., 2012). The KNI-51 speleothem record in the Kimberley's east shows evidence of reduced monsoonal precipitation from 4200 cal. yr BP (Denniston et al., 2013b), whilst a decline in mangrove diversity at ~4000 cal. yr BP in the northeast is argued to be a result of aridity (Proske, 2016). The discrepancies in timing of this event between records may indicate some intra- and inter-site variability, but also are within uncertainty in age control between records.

Wetter conditions at Black Springs appear to return from ~4700 cal. yr BP until ~3400 cal. yr BP as suggested by humification data, organic content and the presence of the aquatic genus Myriophyllum. However, whilst the monsoon appears active at this time taxa indicative of a drier environment increase in abundance including T. timon and Terminalia suggesting that the monsoon is weaker than earlier in the Holocene section of the record. The increase in Pseudoschizaea, which is indicative of desiccation, drought, oxidisation and warmer climates with seasonal drying (Carrión and Navarro, 2002), supports this interpretation of the record. It is likely that Pseudoschizaea has been absent or rare in the record up to this time due to the active monsoon conditions in the early- mid-Holocene. A return to drier conditions between 3400 and 2800 cal. yr BP is also suggested by the humification data, organic content and peak in T. timon, prior to a shift to wetter conditions which persists until 2600 cal. yr BP. Increased late-Holocene climatic variability is also observed at Cape St Lambert in the Kimberley's north as discrete dune building events (Lees et al., 1992).

5.5.1.5 Pronounced late-Holocene aridity

Humification analysis show that the driest phase in the record occurs between 2600 and 1300 cal. yr BP. This is concurrent with a sharp decline in organic content suggestive of decreased productivity and increased aeolian sedimentation due to a much less active monsoon. The slower growth rate during the late-Holocene may also reflect the drier, less productive conditions at the mound and potentially even the deflation of some sediment. There is a shift in vegetation assemblages at 2600 cal. yr BP, with the declining representation of aquatics such as C. dubium and Myriophyllum indicative of reduced standing water at the spring. The abrupt decline of T. timon alongside the continued representation of tropical savanna taxa including Amaranthaceae, Callitris, Asteraceae,

93 Chapter 5

Dodonaea and Terminalia also suggest drier conditions, whilst the reduction in Pseudoschizaea accumulation may reflect the onset of conditions too dry to sustain a large presence of an algal cyst which is typically most abundant in damp soils (Scott, 1992). The pollen assemblages during this time are similar in part to the modern assemblage from the dry shoulder of the mound also suggesting that conditions during the late-Holocene were drier and variable. The tolerance of Pandanus to drought (Elevitch, 2006) may account for its continued presence in this section of the record despite the inferred drier conditions.

Evidence of drier conditions during the late-Holocene can be seen in other records across the Kimberley. For instance, the rapid development of cheniers in the Victoria Delta between 2000 and 1200 yr BP may be the result of reduced fluvial input to the shelf (Lees, 1992). A dust record for this Black Springs core also shows an increase in dust flux to the Kimberley's northwest from the Lake Eyre basin and eastern Simpson Desert indicating anticyclonic circulation and stronger south- easterly trade winds associated with a more northerly ITCZ (McGowan et al., 2012). Speleothem records from the Kimberley's east also show decreasing precipitation from 4200 cal. yr BP with the driest phase occurring 1500 - 1200 cal. yr BP (Denniston et al., 2013b).

5.5.1.6 Transition to modern conditions during the last millennium

A short wet phase is suggested by the humification data from 1300 to 1000 cal. yr BP, with a subsequent change to drier conditions from 1000 - 550 cal. yr BP. There is a change in pollen assemblages at 550 cal. yr BP correlated with shifts seen in the humification record and organic contents to stable values which persist through to present. A sharp increase in grass pollen at 550 cal. yr BP indicates that the surrounding tropical savanna became more open. The simultaneous increase in charcoal accumulation may be related to taphonomic processes since high charcoal accumulation rates have been observed to parallel major vegetation changes in the Australian tropics (e.g. Kershaw et al., 2002; Proske et al., 2014). A peak in T. timon concurrent with a subsequent decline in charcoal accumulation at 260 cal. yr BP is likely to be a response to burning since T. timon is a ready coloniser of disturbed and open sites (Space et al., 2003). In the last ~230 years an increasing abundance of the perennial aquatic C. dubium together with the return of Pandanus to the record can be interpreted as showing a ready supply of water at the site due to active monsoon conditions.

Evidence for active monsoon conditions in the Kimberley over the last couple of centuries are also seen in the Cave KNI-51 speleothem record which shows an elevated number of extreme rainfall events in the last 200 years (Denniston et al., 2015). However, shifts to modern conditions occurring in the last ~550 years are seen elsewhere in the Kimberley such as the development of 94 Chapter 5 modern floodplain settings at Parry Lagoons Wetlands in the northeast from at least 600 cal. yr BP (Proske, 2016). Other northern Australian pollen records indicate a transition to modern conditions during the last millennium (Rowe, 2015; Stevenson et al., 2015). The discrepancies between these records may indicate variability between sites, but may also be a result of dating uncertainties.

5.5.2 Drivers of change

It can be inferred that the increase in monsoonal rainfall seen in the Black Springs record from ~14,000 cal. yr BP is likely to be driven predominantly by post-glacial sea-level rise. The drowning of the Sunda and Sahul shelves following the LGM was an important driver of change in tropical hydroclimate, facilitating increased moisture advection fuelling monsoon activity across tropical Australasia during the late Pleistocene (DiNezio and Tierney, 2013). During the LGM the Joseph Bonaparte Gulf was exposed (Yokoyama et al., 2001b), meaning that the coastline was at least >400 km further away than at present. Micropalaeontological, geomorphological and coral evidence indicates that the sea level rise in the northwest Australian region was moderate from 19,400 cal. yr BP (De Deckker and Yokoyama, 2009) before becoming increasingly rapid in response to Meltwater Pulse 1A at 14,700 - 14,100 yr BP (Hanebuth et al., 2000) ultimately expanding the IPWP and facilitating increases in monsoonal precipitation (De Deckker et al., 2002). Recent high- resolution marine records adjacent to the Kimberley have also proposed that enhanced Southern Hemisphere greenhouse forcing as a result of post-glacial CO2 rise would have accentuated the southward displacement of the ITCZ during the Younger Dryas, and would have contributed to late Pleistocene increases in precipitation across this region (Kuhnt et al., 2015).

Wetter and warmer conditions in general were experienced across tropical Australasia during the early-Holocene (Reeves et al., 2013) with several speleothem records attributing this to the transgression of the Sahul and Sunda shelves (Partin et al., 2007; Griffiths et al., 2009; Denniston et al., 2013a, 2013b). In northwest Australia there is evidence that sea level rise became more rapid in the early-Holocene in response to Meltwater Pulse 1B at 11,500 cal. yr BP (Collins et al., 2011), after which sea level continued to rise until at least the mid-Holocene at ~7000 - 6500 yr BP (van Andel and Veevers, 1967; Collins et al., 2011; Solihuddin et al., 2015). It is therefore likely that the early-Holocene strengthening in monsoon activity seen in this record is primarily driven by the marine transgression.

Drying trends and a contraction of the IPWP are observed in several records across the tropical Australasian region during the mid-Holocene connoting a northward shift of the ITCZ (Reeves et al., 2013). Evidence for a northward shift of the ITCZ at this time comes from the Pacific (Koutavas et al., 2006), Indian (Fleitmann et al., 2003) and Atlantic Oceans (Haug et al., 2001). A northward 95 Chapter 5 shift of the ITCZ would have reduced monsoon activity across northwest Australia as seen in the Black Springs record between ~7000 and 5000 cal. yr BP and in the KNI-51 speleothem record (Denniston et al., 2013b). Increasing climatic variability and drying trends observed in records across tropical Australasia during the late-Holocene (e.g. Donders et al., 2007; Reeves et al., 2013) has been linked to the increase in frequency and amplitude of El Niño from 5000 yr BP seen in several climate models and records (e.g. Moy et al., 2002; Gagan et al., 2004; Conroy et al., 2008). Despite the currently muted effect of El Niño on the monsoon in the Kimberley, Denniston et al. (2013b) suggest that a stronger relationship existed between ENSO and northwest Australia since the late-Holocene possibly due to changes in the mean state of the tropical Pacific. Similarly, McRobie et al. (2015) observed a teleconnection between the northwest and ENSO during the last 3000 years. It is therefore suggested that the increased variability superimposed on a general drying trend from ~5000 cal. yr BP at Black Springs, with a more arid phase from 2600 cal. yr BP to 1300 cal. yr BP, is a result of increases in the frequency and/or intensity of El Niño events. The decreased strength of El Niño from 1500 to 1000 cal. yr BP seen in a number of records (Rein et al., 2004; Stott et al., 2004) may also have been responsible for the wet phase seen in the humification data between 1300 and 1000 cal. yr BP as the La Niña phase became more dominant. The discrepancies in timing of the dry shift between the Kimberley's palaeoclimate records are likely to be due, at least in part, to differences in precipitation gradients across the Australian tropics which are still seen in the region today (e.g. Bureau of Meteorology, 2017).

Denniston et al. (2013b) suggest that the relationship between ENSO and the Kimberley weakened in the last millennium, which may have driven the transition to modern conditions seen at Black Springs in the last 550 years. Fluctuations seen in Australia's archaeological signature during the last ~500 years may be a response by hunter-gatherers to these climate shifts (Williams et al., 2010). The ameliorating climatic conditions may have promoted population expansion in the Kimberley, higher fuel loads and potentially an increase in fire stick farming (McGowan et al., 2012). This may have driven the more open vegetation and elevated charcoal accumulation rates seen at Black Springs from 550 cal. yr BP, as well as in the region's northeast and across the wider Australian tropics.

5.5.3 Impacts of chronological uncertainty

As described in Section 5.4.1, the complicated sequence of 14C dates below 94.5 cm has prevented their inclusion within the age-model presented for BSP00. As a result the maximum constrained age is 9070 cal. yr BP at 94.5 cm, whereas ages below this have been extrapolated based on the age model constructed from dates in the upper portion of the core. The palaeoenvironmental

96 Chapter 5 reconstruction presented in Section 5.5.1 identifies changes broadly synchronous with those identified elsewhere across tropical Australasia, giving some confidence in the extrapolated dates. However, the ages older than 9070 cal. yr BP can still only be treated as approximate and must be regarded with caution. This presents clear limitations in terms of the reliability of the palaeoenvironmental reconstruction from BSP00, posing a challenge for addressing some of the key aims of this thesis (reconstructing climate and environmental change in tropical northwest Australia during the period spanning the LGIT to present). It is therefore essential that a methodology is developed for obtaining robust and accurate age models for organic spring environments before the key objectives of this thesis can be met.

5.6 Conclusions

This extended record from Black Springs provides the first high-resolution reconstruction of environmental change in the Kimberley which encompasses the Holocene period and possibly continues beyond into the late Pleistocene. A geochronological investigation of Black Springs is therefore presented in Chapter 6 in order to resolve this uncertainty. The Black Springs peat archive preserves clear evidence of dramatic changes in the strength of the northwest Australian summer monsoon during this timeframe, with key shifts corresponding with tropical Australasian climatic change during the late Quaternary discussed in the OZ-INTIMATE synthesis (Reeves et al., 2013). Results from Black Springs reveal that the Kimberley's northwest experienced an increase in monsoon activity sometime after ~14,000 cal. yr BP persisting until 7000 cal. yr BP likely driven by post-glacial sea level rise. The monsoon gradually weakened over the next 2000 years with a proposed northward shift of the ITCZ, before becoming more variable and possibly even failing during the late-Holocene associated with enhanced El Niño phases. Modern monsoon activity appears to have been established in the last 600 years.

97 Chapter 6

6 Untangling geochronological complexity in organic spring deposits using multiple dating methods

Chapter 6 is reproduced from the following publication:

Field, E.; Marx, S.; Haig, J.; May, J.-H.; Jacobsen, G.; Zawadzki, A.; Child, D.; Heijnis, H.; Hotchkis, M.; McGowan, H.; Moss, P., 2018. Untangling geochronological complexity in organic spring deposits using multiple dating methods. Quaternary Geochronology 43, 50 – 71.

Chapter 5 confirmed that organic spring deposits in the Kimberley contained proxies amenable to research, but encountered issues with chronological control. This chapter therefore addresses research objectives 5 and 6, firstly by presenting a review of spring chronologies both in isolated locations in arid and semi-arid regions and within larger mire complexes, to identify the complexities involved with building chronologies for organic spring deposits. Based on this review, this chapter then presents the results of a geochronological investigation of three springs in the northwest Kimberley, including Black Springs (cores BSP00 and BSP02), Fern Pool (FRN02) and Gap Springs (ELZ01). This includes the results of 14C and 210Pb dating, auxiliary datasets such as 239+240 210 226 Pu and Ln/Tn, and circumstantial evidence from polonium-210 ( Po) and radium-226 ( Ra) activities of groundwater, and analysis of macro-charcoal fragments by SEM and EDXA. The outcomes of this geochronological investigation facilitates the development of a protocol for building robust chronologies in organic spring deposits, not only in the Kimberley but in all similar environmental settings.

6.1 Introduction

Perennial or ephemeral springs are important palaeoenvironmental archives, particularly in otherwise arid or semi-arid environments (Boyd and Luly, 2005). The use of springs for palaeoenvironmental research requires the preservation of a record within the sediments or organic deposits that accumulate around the spring vent. As demonstrated in Chapter 5, organic deposits are particularly valuable in this context as they preserve a range of palaeoecological proxies, including palynomorphs (pollen and non-pollen), diatoms, molluscs, charcoal, plant macrofossils and humic acids (e.g. Scott, 1982a; van de Geer et al., 1986; Dodson and Wright, 1989; Boyd, 1990b; Macphail et al., 1999; Owen et al., 2004; Dobrowolski et al., 2005; 2012; McGowan et al., 2012; Fluin et al., 2013; Backwell et al., 2014; Dobrowolski et al., 2016; Field et al., 2017). Typically, organic sediments such as peat are formed in saturated and low oxygen conditions since this minimises the rate of decomposition. However, in many springs artesian pressure sustains a water- table “dome” higher than the surrounding terrain, allowing organic material to accumulate above

98 Chapter 6 ground at spring vents when evaporation rates are lower than spring discharge (Ponder, 1986; Boyd, 1990a; McCarthy et al., 2010). Whilst under artesian pressure, capillary creep and slow outward diffusion of groundwater throughout these deposits is sufficient to maintain moisture levels minimising oxidation and desiccation (McCarthy et al., 2010). In addition to palaeoecological indicators organic spring deposits can preserve a range of other palaeoenvironmental information such as stable isotope ratios, geochemical tracers and rates of dust deposition through time (e.g. Dobrowolski et al., 2005, 2012, 2016; McGowan et al., 2012; Mazurek et al., 2014).

In arid and semi-arid environments establishing continuous records of Quaternary environmental change is challenging due to the lack of perennial water sources (e.g. lakes) that preserve robust sedimentary records. Records from those water bodies that do exist, such as ephemeral lakes, commonly contain chronological hiatuses, for example during dry periods when deposition may cease, or unconformities due to aeolian deflation and scouring during heavy rainfall and floods (Head and Fullager, 1992; Magee et al., 2004). In addition, these environments have limited fossil preservation due to oxidation during dry periods. As such, important palaeoenvironmental and climatic information has been derived from organic springs in the arid and semi-arid environments of Australia (e.g. Chapter 5; Dodson and Wright, 1989; Boyd, 1990b; McGowan et al., 2012; Fluin et al., 2013; Field et al., 2017), Kenya (e.g. Owen et al., 2004), Jordan (Rambeau, 2010) and South Africa (e.g. Scott, 1982a, 1982b; Scott and Vogel, 1983; Scott, 1988; van Zinderen Bakker, 1989; Scott and Cooremans, 1990; Scott and Nyakale, 2002; Truc et al., 2013), with some records spanning up to ∼37,000 years (e.g. Fluin et al., 2013). For instance, pollen analysis at Wonderkrater spring mound has yielded a ∼35,000 year record of climatic evolution (Scott, 1982b), and more recently quantitative climatic estimates from pollen-transfer functions (Truc et al., 2013), whilst diatom transfer functions from a spring at the Campground Wetlands in Kenya have been used to provide pH, conductivity and temperature estimates for part of the late-Holocene (Owen et al., 2004). Spring deposits have also been shown to be viable traps for aeolian dust. For example, a ∼6500 year record of dust accumulation was constructed for Black Springs, one of the study sites investigated in this paper (McGowan et al., 2012). In that study, patterns in dust flux through time were used to investigate changing moisture regimes which were linked to changing patterns in the Australian monsoon.

Outside of arid and semi-arid regions, springs within larger mire complexes have also been used to reconstruct valuable palaeoenvironmental records, for example in Poland (e.g. Dobrowolski et al., 2005, 2012, 2016; Mazurek et al., 2014) and Australia (e.g. van de Geer et al., 1986; Macphail et al., 1999), with some records encompassing at least ∼52,000 years (e.g. van de Geer et al., 1986).

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Since springs are a focus of human and faunal activity in water scarce regions they are also an important source of palaeontological and archaeological information. Consequently, occupational and faunal remains have been found surrounding springs (e.g. Hughes and Lambert, 1985; Veth, 1989) and within their sediments (e.g. Potezny, 1978; Kuman and Clarke, 1986; Backwell et al., 2014) up to ∼138,000 years before present (BP) (e.g. Backwell et al., 2014). Springs have particular importance in arid Australia and feature prominently in the songlines and myths of indigenous Australians (Harris, 2002). They were also of strategic importance to early European explorers in Australia, acting as vital “stepping stones” across the arid interior of the continent (Harris, 1981).

Despite the potential of organic spring deposits to be excellent archives of palaeoenvironmental and climatic information, as demonstrated in Chapter 5 there are a number of complications in the application of standard 14C techniques. This, in many cases, has led to confusing chronologies in springs (e.g. Scott and Vogel, 1983; Kuman and Clarke, 1986; Scott, 1987; Boyd, 1990a; Macphail et al., 1999; Scott et al., 2003; Dobrowolski et al., 2012; Mazurek et al., 2014; Field et al., 2017) (see Section 6.1.2; Figure 6.2 and Figure 6.3) which may compromise the integrity of environmental, climatic, palaeontological and archaeological reconstructions.

The aim of this study was therefore to establish a protocol for building reliable chronologies for organic spring deposits through the analysis of dates generated using multiple methodologies, utilising springs from the Kimberley region of northwest Australia as an example. The Kimberley is also of importance as there remains a limited understanding of palaeoenvironmental and climatic change in Australia's tropical savanna (Reeves et al., 2013), as outlined in Chapters 1 and 3. It is also an area within which multiple organic springs have been identified (see Chapter 2; Department of Environment and Conservation, 2012; Field et al., 2017) and is an environment where there are few other opportunities to construct detailed chronological records of the recent past. Dates from three springs in the Kimberley are obtained via AMS and standard radiometric 14C dating with AAA and HyPy pre-treatments on a number of carbon fractions for this study (pollen concentrate, macro-charcoal, bulk organics, SPAC and roots). For the uppermost sediments, chronological control is attempted using 210Pb and 239+240Pu analysis. Supporting chronological information is provided by analysis of the 210Po and 226Ra activities of groundwater, macro-charcoal investigation, and the application of luminescence techniques at high spatial resolution (Ln/Tn). The ability to build reliable chronologies for organic spring sediments is important to enable researchers to obtain accurate, high-resolution palaeoclimate and environmental records. This is of particular concern in arid and semi-arid regions which are typically challenging for Quaternary research. Additionally,

100 Chapter 6 reliable chronologies from organic spring deposits will facilitate improved interpretation of the age of cultural artefacts and faunal remains found in their sediments.

6.1.1 Conceptual sources of geochronological complexity in organic spring deposits

Within organic springs there are a number of processes that have the potential to complicate the geochronological integrity of sedimentary deposits (Figure 6.1). These processes include aeolian and alluvial input, root growth, upwelling groundwater, weathering, bioturbation, and mass movement within the spring.

Allochthonous transport of biological material to the spring by aeolian or alluvial processes has the potential to introduce “old” carbon, affecting 14C ages. This can include “old” charcoal which may remain in the surrounding landscape due to its presumed long-term environmental persistence, despite some evidence suggesting that it may not be as stable as originally thought (see Bird, 2007 and references within). The protuberant morphology of the spring mound above the surrounding landscape reduces the likelihood of “old” carbon washing into the spring sediments. However, alluvial input may occur during the spring's early stages before development of a mound see Section 5.1.1; Ponder, 1986; Field et al., 2017), or during large floods when the mound is small but prone to inundation. Over time charcoal in the landscape may be broken down into finer fractions (Walker, 2005; Bird, 2007) which can then be blown into the spring during any stage of its development. Transport of “old” carbon into springs by these mechanisms may compromise their age structure.

Perennial springs, or those where oxygenated ground water supports enhanced plant growth, can contain deep rooted vegetation (Scott and Vogel, 1983) introducing young carbon into the spring deposits (Boyd, 1990b). Depending on the fraction dated, this young carbon cannot easily be removed from other biological fractions since separation methods (e.g. density separation or acid digestion) will also affect the organics targeted for 14C dating. Removing rootlets by hand is extremely time consuming and not possible in all cases. Rootlets can also penetrate large charcoal fragments selected for dating by growing along the original wood fibres (Harkness et al., 1994), thereby compromising the age of the charcoal fragment. In addition, the decay of roots can facilitate transport of young biological material or sediment via root channels affecting geochronology. These root channels may also allow the movement of other radiological sediment markers such as 210Pb and 239+240Pu to shift downwards in the profile.

In springs upwelling groundwater is related to recharge from precipitation (McCarthy et al., 2010). During periods of decreased rainfall a lower water table can facilitate desiccation of the organic

101 Chapter 6 sediments (Scott, 2016). If springs then become dry, aeolian deflation may remove part of the deposit, while onset of rainfall could result in downward transport of sediment and biological substances through the peat matrix. In addition, springs may also experience cracking and self- mulching leading to mixing and overturning of mound stratigraphy. Alternatively, during periods of high spring discharge there is potential for upward movement of sediment and biological material, whilst sediments may also be removed via scouring during the spring's early stages before a mound develops. These processes may cause 14C, 210Pb, fallout radionuclide and luminescence results to be unreliable.

Water table fluctuations can cause in-situ alterations to charcoal preserved in the sediments (e.g. Bird et al., 2002) affecting returned 14C ages. Because of the large surface area and porous nature of charcoal it lends itself to adsorption of various organic and inorganic compounds (Bird, 2007). This makes it an ideal substrate for microbial colonisation which allows continued carbon cycling between fossilised charcoal and the modern environment (Zackrisson et al., 1996), and facilitates replacement of the original carbon by various oxides and oxihydroxides (Bird et al., 2002). Charcoal may also undergo oxidative degradation (Cohen-Ofri et al., 2006), particularly in coarser matrixes, as a result of bacterial activity and weathering, which may occur during periods when the water table is lower. It has been demonstrated that removal of charcoal contamination with 14C pre- treatments such as AAA or even the more rigorous acid-base-oxidation with stepped combustion (ABOX-SC) methodology is not always effective (e.g. Gillespie et al., 1992; Harkness et al., 1994; Bird et al., 2002; Higham et al., 2009a, 2009b), particularly in high weathering environments, where contaminants can irreversibly react with, and alter, the charcoal surface (Bird, 2007). Charcoal in organic spring deposits may therefore be contaminated with young carbon, particularly in cases where there have been large water table fluctuations.

Upwelling groundwater through organic spring deposits can also render them open systems in regards to uranium, which may be leached from host rocks/sediments and transported in solution within groundwater (Sirocko et al., 2007). This can affect U-series dating, including 210Pb. Organic decomposition products such as fulvic and humic acids are capable of adsorbing large quantities of uranium, which bind strongly to clay minerals in organic sediments (Szalay, 1969; van der Wijk et al., 1986). Therefore the decomposition of organic matter and low redox potential of peat deposits make them ideal environments for the geochemical trapping of uranium (Shotyk, 1988). This can result in uranium-enriched organic deposits (e.g. Heijnis, 1992; Heijnis and van der Plicht, 1992; Zayre et al., 2006) even where relatively low concentrations of uranium are observed in the groundwater (e.g. Armands, 1967). Uranium and associated daughter products such as 210Po and

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226Ra can therefore be high in organic spring sediments which may complicate the use of 210Pb as a geochronological tool by masking unsupported 210Pb activities.

Internal physical processes within springs can also influence their age stratigraphy. This includes slumping of the spring mound, if they develop too steeply, or if the vent position changes. As a focal point for animals, springs can also be affected by bioturbation (Scott, 2016). In Australia, this may be more pronounced after the arrival of Europeans and the introduction of domestic livestock, which occurred from the 1800s in the Kimberley.

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6.1.2 Common chronological issues in organic spring deposits

Existing palaeoenvironmental records from organic springs overwhelmingly rely on 14C dating, however the majority of published 14C chronologies are complicated by age-depth reversals and/or erroneously young dates. This is demonstrated in Chapter 5, and Figure 6.2 and Figure 6.3, which depict age-depth profiles characteristic of organic springs presented in earlier published works, both from isolated dryland springs (Figure 6.2) and from springs within larger mire complexes (Figure 6.3) (see figure captions for publication details). The plotted profiles come from a variety of global locations (Figure 6.4), in which the carbon fraction dated consists predominantly of either bulk organics or pollen concentrate, with the exception of Dalhousie Springs, Scot, Meriba Springs and Rietvlei (Figure 6.2A, Figure 6.2G, Figure 6.2I and Figure 6.2J) where the carbon fraction dated is unknown, and Zawadówka, Mowbray Swamp and Pulbeena Swamp (Figure 6.3M, Figure 6.3T and Figure 6.3U) where a number of other fractions were analysed including macrofossils, root stumps and humic extracts.

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The chronologies of the plotted records are predominantly characterised by either sudden increases in age over narrow depth intervals (Figure 6.2A and Figure 6.3N), unreasonably high sedimentation rates (Figure 6.2A, Figure 6.2E and Figure 6.2O), or more commonly age reversals (Figure 6.2B, Figure 6.2D, Figure 6.2G, Figure 6.2H, Figure 6.2J, Figure 6.2L, Figure 6.3M, Figure 6.3N, Figure 6.3P - R). The latter implies complexity of carbon sources within the springs, while the former could represent contamination of the preceding layer with younger carbon, or perhaps indicate unconformities or growth hiatuses in the springs as a result of aeolian deflation or scouring. Age reversals are also seen in the Mowbray Swamp and Pulbeena Swamp chronologies (Figure 6.3T and

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Figure 6.3U) and whilst the authors note the presence of trace contamination at these sites, these reversals may be due in part to dates being near the 14C barrier (van de Geer et al., 1986). There are also a number of examples where ages are contradictory between corresponding cores or pits surveyed at the same site and similar depth (Figure 6.2B, Figure 6.2C, Figure 6.2G and Figure 6.2L).

The extent of complications in 14C chronologies within organic springs is further illustrated by the fact that, to the best of my knowledge, there are just four published studies where the spring chronology is free from complications (Figure 6.2F, Figure 6.2I, Figure 6.2K and Figure 6.3S). In one of these studies at Florisbad Spring, South Africa, an earlier study had previously found erratic 14C ages which were attributed to contamination of 14C by roots (Kuman and Clarke, 1986). In the later study of Scott and Nyakale (2002), a concerted effort to remove root fragments from bulk organic 14C was undertaken, resulting in a coherent age-depth profile for the site, i.e. ages increased with depth (Figure 6.2K). Therefore, although existing studies have highlighted the value of organic spring deposits as palaeoenvironmental archives, in most cases the information contained is convoluted by the problematic geochronology.

Figure 6.4. The location of springs plotted in Figure 6.2 and Figure 6.3

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6.2 Physical setting

Sediment cores from three springs in the northwest Kimberley are analysed in this study; Black Springs, Fern Pool and Gap Springs (Figure 6.5). For full location, climate and vegetation details for these study sites, please refer to Section 2.5. The climate is monsoonal with a mean annual rainfall of ~1000 mm/yr. When combined with a mean annual potential evapotranspiration of ~1900 mm/yr and high seasonality (>70% of precipitation falling between January and March) (Bureau of Meteorology, 2017) this creates a water-limited environment within which these springs occur.

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As described in Section 2.5, of the studied springs, Black Springs has the most prominent mound (approximately 2 m in height above the surrounding landscape), while Fern Pool is less elevated above the landscape and Gap Springs has no topographic protuberance. These differences in mound morphology are likely attributable to discharge, with Black Springs having more vigorous groundwater discharge by comparison to Fern Pool and Gap Springs. The springs are heavily vegetated in contrast to the surrounding tropical savanna.

6.3 Materials and methods

6.3.1 Core collection and description

The three springs examined in this study (Black Springs, Fern Pool and Gap Springs) were cored during the Kimberley’s dry season in June, 2015 using a 50 cm long Russian D-section corer. A core was also collected from Black Springs in 2005 (BSP00) and was previously described in Chapter 5, McGowan et al. (2012) and Field et al. (2017). Ages from that core are presented here for comparison. Cores BSP02, FRN02 and ELZ01 were photographed on the Itrax µXRF core scanner at the Australian Nuclear Science and Technology Organisation (ANSTO) before being described using standard stratigraphic techniques including Munsell colour and field-texture analysis. Organic content of the cores were determined by LOI following Heiri et al. (2001).

6.3.2 Carbon-14 dating

In this study, four carbon fractions; pollen concentrate, macro-charcoal, SPAC and roots were dated by 14C. Carbon stable isotope ratios were determined using an Isotope Ratio Mass Spectrometer (IRMS δ13C) for 14C measurement correction. No macrofossils suitable for 14C dating were found.

In BSP02, FRN02 and ELZ02 initial samples of pollen concentrate and macro-charcoal were extracted at the same, or similar, depths wherever possible to facilitate comparisons between results. Sample locations were selected where radiograph imagery indicated minimal root disturbance. Some initial macro-charcoal and pollen concentrate dates contained inconsistencies and age reversals (see Figure 6.7), so to help clarify core geochronology and better understand the source of 14C inconsistencies in the springs SPAC was also extracted from selected depths throughout BSP02, FRN02 and ELZ01. During density separation of pollen concentrate, it was noted that small root fragments floated off along with the pollen. It was considered that these roots may have introduced younger 14C, increasing the 14C:12C ratio and decreasing pollen concentrate ages. For this reason, roots from the basal pollen samples of BSP02 and FRN02 were extracted for dating for comparison with the ages returned on SPAC and charcoal fractions.

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For core BSP00, dates were obtained on pollen concentrate and bulk organic fractions. To better understand 14C sources in this core, two bulk organic samples (humins) were also dated, one by standard 14C radiometric techniques (Wk-41825) and one by AMS due to its small sample volume (Wk-41826).

All samples were calibrated using the OxCal program (V4.2.4.) (Bronk Ramsey, 2013) and the Southern Hemisphere calibration curve (SHCal13) (Hogg et al., 2013), with 0 cal. yr BP representing 1950 AD.

6.3.2.1 Pollen concentrate

Extraction of pollen for dating was adapted from the method outlined in Moss (2013). Seventeen sediment samples (three from both BSP02 and FRN02, two in ELZ01, and nine in BSP00) were disaggregated with 10% Na4P2O7 for one hour then passed through a series of sieves (2 mm, 500 µm, 150 µm and 8 µm diameter mesh) to collect roots (>2 mm and 500 µm fractions) and pollen (<150 µm and >8 µm fraction). Unwanted inorganic material was removed from the pollen via density separation with Na6.(H2O40W12) at specific gravity 1.9. In addition, the 2015 core samples were cleaned with 40% hydrofluoric acid (HF) to remove residual silicates. Remaining organics 14 were washed in Milli-Q water and retained for C analysis.

Pollen concentrate samples were pre-treated using the AAA technique following Hatté et al. (2001). Sequential washings of hydrochloric acid (HCl) to remove carbonates, repeated sodium hydroxide (NaOH) washes to remove fulvic and humic acids, and HCl to remove any atmospheric carbon dioxide (CO2) absorbed during alkali treatment, were performed. Samples were combusted at 900

°C to convert them to CO2, followed by graphitisation using the H2/Fe method (Hua et al. 2001). Carbon-14 measurement of pollen concentrate from BSP02, FRN02 and ELZ01 was undertaken by AMS on the ANTARES and STAR accelerators at ANSTO (Fink et al., 2004), whilst pollen concentrate from BSP00 was submitted to Waikato Radiocarbon Dating Laboratory for processing with AMS measurement undertaken at the W.M Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory, University of California.

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6.3.2.2 Macro-charcoal

Extraction of macro-charcoal followed the method outlined in Stevenson and Haberle (2005). Ten samples (four from both BSP02 and FRN02, two from ELZ01) were disaggregated with 10%

Na4P2O7 heated to 100 °C, then passed through a 125 µm sieve with the >125 µm fraction retained.

The retained samples were treated with 6% hydrogen peroxide (H2O2) to bleach organic material and facilitate identification of charcoal. Charcoal was identified under a binocular microscope and hand-picked into Milli-Q water using titanium high precision tweezers. The picked charcoal was dried at 60 °C with a target dry weight of >2 mg assuming some material would be lost during AAA pre-treatment. Samples were pre-treated using AAA, combusted and graphitised as described in Section 6.3.2.1 and were measured by AMS at ANSTO.

6.3.2.3 Bulk organics

Two bulk organic samples from BSP00 were submitted to Waikato Radiocarbon Dating Laboratory. Visible contaminants were removed before samples were pre-treated using AAA, combusted and graphitised as described in Section 6.3.2.1. Sample Wk-41826 was measured for 14C by AMS (as previously described) whilst the larger mass of sample Wk-41825 enabled it to be measured by Liquid Scintillation Spectrometry on a Perkin Elmer 1220 “Quantulus” Liquid Scintillation spectrometer.

6.3.2.4 Stable polycyclic aromatic carbon (SPAC)

HyPy is a relatively new 14C pre-treatment methodology, where samples undergo pyrolysis aided by high hydrogen pressures in the presence of a dispersed sulphided molybdenum catalyst (Ascough et al., 2009). This method isolates the SPAC component of a sample by removing >92% of the labile organic material including contaminants (Ascough et al., 2009; Bird et al., 2014). Twelve samples (three from FRN02, four from BSP02 and five from ELZ01) were treated by HyPy at James Cook University following the approach of Ascough et al. (2009) and Meredith et al. (2012). Aliquots of each sample (~1 g) were loaded with a dispersed sulphided molybdenum catalyst (~10% by weight) using an aqueous MeOH solution of ammonium dioxydithiomolybdate ({NH4}2MoO2S2), sonicated for 15 minutes, then dried overnight at 70 °C in a vacuum oven. These samples were placed in the

HyPy reactor, pressurized with hydrogen (H2) to 150 bar with a gas flow of 4 litres/minute. The HyPy residues were combusted and graphitised as described in Section 6.3.2.1 and measured by AMS at ANSTO.

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6.3.2.5 Roots

Roots >2 mm retained during sieving for the pollen fraction were collected from the basal sample of both BSP02 and FRN02. Samples were submitted to Beta Analytic where they were pre-treated using AAA, combusted and graphitised as described in Section 6.3.2.1 and measured by AMS.

6.3.3 Lead-210 dating

Eight samples through the top 70 mm in BSP02 and FRN02 and 18 samples through the top 310 mm in ELZ01 were dated using 210Pb at ANSTO. Sediment ages were determined from unsupported 210Pb activity using the constant initial concentration (CIC) (Robbins and Edgington, 1975) and constant rate of supply (CRS) (Appleby and Oldfield, 1978) models. Supported 210Pb was determined by measuring 226Ra, while total 210Pb was determined by measuring 210Po, both of which are assumed to be in secular equilibrium with 210Pb. Unsupported 210Pb activity was calculated as the difference between supported 210Pb and total 210Pb activity. Samples were dried at 60 °C for 48 hours in order to calculate moisture content, with dry bulk density calculated using Equation (1. Separation and analysis of 226Ra and 210Po began by adding isotopic tracers of barium- 133 (133Ba) and polonium-209 (209Po) to 0.2 g dried sediment. Samples were digested in a 226 210 combination of nitric acid (HNO3), H2O2 and HCl to extract Ra and Po from the sample matrix. Polonium-209+210 were auto-deposited onto silver disks and counted by high-resolution 226 133 alpha spectrometry, whilst Ra and Ba were co-precipitated with barium sulfate (BaSO4) and collected on membrane filters. Barium-133 was counted on a high purity germanium (HPGe) gamma detector to determine its recovery which is used to estimate the recovery of 226Ra. The activity of 226Ra was determined by high-resolution alpha spectrometry. Sample ages were corrected for moisture content and dry bulk density.

( )

3 (1) ρ = Dry bulk density (g/mL); Swm = Sample wet mass (g); Swv = Sample wet volume (m ); θs = Sample moisture content (%)

6.3.4 Plutonium-239+240 chronostratigraphic markers

Plutonium-239+240 activities in ELZ01 and BSP02 were analysed as an additional chronostratigraphic marker. These isotopes have the same anthropogenic source as caesium-137 (137Cs), i.e. derived from nuclear weapon test fallout, however they have a longer half-life (24,110 years for 239Pu and 6,561 years for 240Pu compared to 30 years for 137Cs (Browne and Tuli, 2006,

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2007, 2014) enabling detection in far smaller sediment masses. In addition, 239+240Pu analysis by AMS has a better sensitivity than 137Cs measured by gamma spectrometry. Plutonium-239+240 activities are therefore ideal as chronological markers for identifying the period between the early 1950s and 1964, i.e. the beginning and peak of nuclear weapons testing fallout. Plutonium-239+240 activities were measured in nine samples in the top 130 mm in ELZ01 and six samples in the top 90 mm in BSP02. Samples were prepared following Child et al. (2008) whereby they were ashed at 800 °C to remove organic soil components, plutonium-242 (242Pu) and uranium-233 (233U) were added as isotope dilution tracers, leached with 10 mL aqua regia (3:1 HCl:HNO3) to solubilize stratospheric fallout Pu, then purified by ion extraction chromatography (Eichrom TEVA® resin).

The separated Pu was co-precipitated with iron(III) oxide-hydroxide (Fe{OH}3), then dried and calcined to form an iron oxide matrix for AMS analysis. Measurement was undertaken by AMS on the VEGA accelerator at ANSTO (Wilcken et al., 2015). PuO- ions were injected into the accelerator which was operated at 0.6 MV. Using helium gas stripping Pu3+ ions were selected for analysis after acceleration, yielding greater than 30% particle transmission efficiency. Plutonium- 230+240 are quantified relative to the known amounts of 242Pu added to each sample by measurement of the 239/242 and 240/242 isotope ratios.

6.3.5 Supporting chronological information

6.3.5.1 Luminescence analysis

Aeolian transportation of sand sized grains into the spring deposits enables the use of a modified luminescence screening approach (e.g. Sanderson and Murphy 2010; Munyikwa and Brown 2014) to determine whether mixing of the sediment profile or subtle stratigraphic breaks could be responsible for the erratic age-depth relationships frequently observed in organic spring 14C chronologies. Twenty five samples from BSP02 were extracted in a dark room under red light at 5 – 10 cm intervals from the central portion of the core to reduce the risk of light exposure. These samples were then digested in a dark-room in 6% H2O2. Three 6 mm aliquots from each sample were prepared on steel discs from the remaining detrital material.

To enable direct comparability between aliquots while allowing time effective measurement as necessary for achieving high spatial resolution through the core, the first cycle of standard post-IR OSL SAR protocols (e.g. Murray and Wintle, 2000; Wintle and Murray 2006) were measured on a Lexsyg smart device (Richter et al., 2013) at The University of Freiburg, Germany. The natural luminescence signal (Ln) was measured by preheating the aliquots to 210 °C for 10 s prior to all measurements, followed by 100 s of infra-red stimulation (IRSL, 850 nm peak emission, 130 mW cm-2), and 40 s of blue light stimulation (BSL, 458 nm peak emission, 50 mW cm-2). The IRSL 113 Chapter 6 signal was recorded for 85 s while the BSL signal was recorded for 40 s with a Hoya-U340 filter in combination with a Delta-BP 365/50 Interference Filter. Additionally, a Schott NG-4 AHF Brightline HC414/46 Interference filter and a Schott NG-11 filter were used to avoid overexposure for particularly bright aliquots. A test signal (Tn) was subsequently determined by repeating the measurement after an application of a beta test dose of 99 Bs. The first 8 and 0.6 s of the recorded IRSL and BSL signals, respectively, were used for integration by subtracting the signal between and 75 - 85 s (IRSL) and 25 - 30 s (BSL) as background. The down-core variation of the resulting normalized luminescence signal (Ln/Tn ratio) was then interpreted.

6.3.5.2 Examination of macro-charcoal

Due to inconsistencies in the macro-charcoal 14C dates (as presented in Section 6.4.2), charcoal sub- samples from the 14C samples were examined for charcoal alteration. Fragments were examined by scanning electron microscopy (SEM) with element distributions obtained via SEM energy dispersive X-ray analysis (EDXA) on a Hitachi TM3030 desktop SEM with Bruker EDS at The University of Queensland.

6.3.5.3 Polonium-210 and 226Ra activities of groundwater

The activities of 210Po and 226Ra were measured in the groundwater at each of the three springs to assess if U-series isotopes in groundwater could be affecting sediment 210Pb activities. Samples of spring water were collected from each site during the 2015 field campaign, with 50 mL of each sample passed through a 0.45 µm filter. Both the filtrate (groundwater) and residue (organic material) from each sample were analysed by alpha spectrometry for 210Po and 226Ra activities using the method described in Section 6.3.3 at ANSTO.

6.4 Results

6.4.1 Core lithology

Sedimentary sequences for BSP02, FRN02 and ELZ01 are shown in Figure 6.6. The BSP02 core (242 cm) collected from Black Springs consists of approximately 80 cm of black, well decomposed peat (70% organic content by weight). Between 80 - 175 cm the organic content decreases down- core whilst the clay content increases. A marked change to organic silty clay occurs at 175 cm (organic content <20%), with the silty clay content increasing below 200 cm (organic content <10%).

The FRN02 core (204 cm) collected from Fern Pool consists of a 10 cm root mat, underlain by brown, poorly decomposed peat. At 55 cm the degree of peat decomposition increases and the peat

114 Chapter 6 becomes darker. At 125 cm there is a change to organic silty clay, the colour of which becomes lighter grey with depth. The lower portion of the core contains titanium oxide/aluminium oxide

(TiO/Al2O3) concretions (below 124 cm).

The ELZ01 core (140 cm) collected from Gap Springs consists of a short organic layer (up to 50% organic content) at the top of core (0 - 25 cm). Below this the core consists of grey organic silty clay overlying a sand layer at 120 cm. All three cores have abundant roots throughout.

Figure 6.6. Generalised stratigraphy, organic content and photographs of cores BSP02, FRN02 and ELZ01

6.4.2 Carbon-14 dates

All results from 14C analysis are presented in Table 6.1 and Figure 6.7. Dates are presented in the text as the upper and lower limits of all the possible calibrated age ranges at 2σ (cal. yr BP). Carbon-14 dates of different carbon fractions in the cores at the same or similar depths, in some cases, returned different ages (Figure 6.7). Consequently the age structure of each carbon fraction in each core is described in the following sections.

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Table 6.1. 14C dates and calibrated ages for all samples from cores BSP02, FRN02, ELZ01 and BSP00

Median Pre- 14C age Calibrated age (cal. yr Calibrated age Lab. ID Fraction dated depth treat (BP)1 BP)2*+ range2* (cm) ment BSP02 OZT910 Macro-charcoal 39 AAA 1760±30 1543 - 1709 (100%) 1543 - 1709 Wk-44690 SPAC 75 HyPy 3014±20 3060 - 3227 (99.6%) 3040 - 3227 3040 - 3043 (0.4%) OZT911 Macro-charcoal 111 AAA 6630±40 7425 - 7571 (100%) 7425 - 7571 OZT166 Pollen 113.5 AAA 5560±40 6273 - 6404 (95.1%) 6218 - 6404 6218 - 6236 (4.9%) Wk-44691 SPAC 149 HyPy 6430±23 7258 - 7420 (100%) 7258 - 7420 OZT912 Macro-charcoal 186.5 AAA 8890±60 9677 - 10189 (100%) 9677 - 10189 Wk-44692 SPAC 188.5 HyPy 8944±29 9900 - 10190 (100%) 9900 - 10190 OZT165 Pollen 189 AAA 7910±45 8548 - 8788 (89.2%) 8548 - 8971 8830 - 8864 (4.6%) 8917 - 8971 (5.4%) 8886 - 8894 (0.8%) OZT913 Macro-charcoal 221 AAA 9065±50 10154 - 10250 (95.8%) 9967 - 10250 9967 - 9983 (4.2%) OZU455 SPAC 233 HyPy 12100±40 13755 - 14085 (100%) 13755 - 14085 OZT164 Pollen 240.5 AAA 9030±45 10121 - 10238 (68.3%) 9929 - 10238 9929 - 9996 (18.1%) 10004 - 10064 (13.6%) Beta-426153 Roots 240.5 AAA 4140±45 4437 - 4825 (100%) 4437 - 4825 BSP00 Wk-29127 Pollen 23 AAA 516±35 493 - 546 (100%) 493 - 546 Wk-28374 Pollen 45.5 AAA 3455±30 3572 - 3726 (92%) 3572 - 3821 3793 - 3821 (6.1%) 3750 - 3763 (1.9%) Wk-29128 Pollen 55.5 AAA 4671±32 5343 - 5466 (76.1%) 5298 - 5466 5298 - 5337 (23.9%) Wk-29129 Pollen 79.5 AAA 6938±37 7659 - 7833 (100%) 7659 - 7833 Wk-28376 Pollen 95 AAA 8186±35 9001 - 9145 (84.5%) 9001 - 9252 9166 - 9252 (15.5%) Wk-29130 Pollen 104.5 AAA 7081±40 7786 - 7961 (98.9%) 7763 - 7961 7763 - 7772 (1.1%) Wk-41825 Bulk 118.2 AAA 6151±84 6746 - 7248 (100%) 6746 - 7248 Wk-28377 Pollen 127 AAA 5713±30 6397 - 6537 (98.4%) 6354 - 6537 6354 - 6364 (1.6%) Wk-29131 Pollen 140.5 AAA 7439±36 8161 - 8341 (98.2%) 8068 - 8341 8068 - 8082 (1.8%) Wk-28375 Pollen 153 AAA 7033±31 7707 - 7934 (100%) 7707 - 7934

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Wk-41826 Bulk 164.8 AAA 5437±22 6178 - 6284 (91.6%) 6033 - 6284 6120 - 6147 (7.9%) 6033 - 6036 (0.5%) FRN02 OZU460 SPAC 48.5 HyPy 1215±25 1047 - 1119 (49.8%) 983 - 1177 1128 - 1177 (25.2%) 983 - 1030 (25%) OZT918 Macro-charcoal 50 AAA 1030±30 801 - 956 (100%) 801 - 956 OZU461 SPAC 95 HyPy 3505±25 3637 - 3835 (100%) 3637 - 3835 OZT916 Macro-charcoal 97 AAA 1315±30 1089 - 1276 (100%) 1089 - 1276 OZT163 Pollen 99.5 AAA 3395±40 3466 - 3697 (100%) 3466 - 3697 OZT162 Pollen 148 AAA 6960±40 7666 - 7848 (100%) 7666 - 7848 OZT917 Macro-charcoal 149.5 AAA 6980±210 7430 - 8182 (100%) 7430 - 8182 OZU462 SPAC 195.5 HyPy 10110±35 11392 - 11814 (99.1%) 11357 - 11814 11357 - 11373 (0.9%) OZT919 Macro-charcoal 198.25 AAA 700±40 553 - 673 (100%) 553 - 673 OZT161 Pollen 201 AAA 3510±40 3612 - 3857 (100%) 3612 - 3857 Beta-426153 Roots 201 AAA 1290±30 1068 - 1271 (100%) 1068 - 1271 ELZ01 OZU456 SPAC 35 HyPy 3175±25 3322 - 3407 (68.9%) 3251 - 3443 3251 - 3305 (26.3%) 3426 - 3443 (4.8%) OZT914 Macro-charcoal 50 AAA 875±30 680 - 793 (100%) 680 - 793 OZU457 SPAC 56 HyPy 5355±35 5987 - 6211 (95.9%) 5946 - 6265 5946 - 5969 (2.5%) 6247 - 6265 (1.6%) OZU458 SPAC 76 HyPy 7790±35 8424 - 8599 (100%) 8424 - 8599 OZT915 Macro-charcoal 85.5 AAA 5440±60 5996 - 6304 (100%) 5996 - 6304 OZT169 Pollen 89 AAA 1475±25 1297 - 1365 (100%) 1297 - 1365 Wk-44693 SPAC 95.75 HyPy 8859±33 9686 - 9960 (79%) 9686 - 10151 10056 - 10151 (15.5%) 9987 - 10043 (5.5%) OZU459 SPAC 116.25 HyPy 12430±45 14129 - 14811 (100%) 14129 - 14811 11σ errors are given for 14C ages (reported at 68% probability) 22σ errors are given for calibrated ages (reported at 95.4% probability) *Calibrated against SHCal13 (Hogg et al., 2013) with OxCal V.4.2.4 (Bronk Ramsey, 2013) +Since calibration of 14C years to calendar years can result in a number of age ranges, the calibrated age ranges encompassing the largest proportion of total probability (%) are shown in bold and italicised font.

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6.4.2.1 BSP02

Carbon-14 ages for BSP02 range from 1543 – 14,085 cal. yr BP, although age ranges for various carbon fractions differ. All of the fractions where multiple 14C dates were obtained display coherent age-depth relationships, i.e. ages increase with depth (Figure 6.7A), with the exception of the root fragments at the base of the core (sample Beta-426153, 240.5 cm), which are younger than the dates above (younger than all other dates returned below ~100 cm). It should be noted that macro-

118 Chapter 6 charcoal dates begin plateauing towards the base of the core. Samples OZT912 and OZT913 record overlapping age ranges (9677 – 10,189 and 9967 – 10,250 cal. yr BP, respectively) despite the two ages being 34.5 cm apart.

Dates from identical or similar depths on various carbon fractions returned differing results (outside of error). For example, macro-charcoal and pollen at 111 cm and 113.5 cm returned ages which differed by >1000 years (7425 – 7571 and 6218 – 6404 cal. yr BP, respectively), dates at 186.5 – 189 cm gave ages of 8548 - 8971 (pollen), 9677 - 10189 (macro-charcoal) and 9900 – 10,190 cal. yr BP (SPAC), and at the base of the core (221 – 241.5 cm) ages ranged from 4437 - 4825 (roots), 9929 – 10,238 (pollen), 9967 – 10,250 (macro-charcoal), and 13755 – 14,085 cal. yr BP (SPAC) (Figure 6.7A, Table 6.1).

Of the four different carbon fractions there is only one instance where age ranges overlap at similar depths. This occurs at 186.5 cm where macro-charcoal returned an age of 9677 – 10,189 and at 188.5 cm SPAC returned an age of 9900 – 10,190 cal. yr BP. Although as noted above pollen from a similar depth recorded a younger age.

6.4.2.2 BSP00

Ages for the BSP00 core (Chapter 5; McGowan et al., 2012; Field et al., 2017) display a very different pattern to those from BSP02 despite both cores being collected from the same spring (Black Springs). Ages in the top 95 cm of BSP00 increase with depth, however these are older than ages for comparative depths in the top ~150 cm of BSP02. For example, in BSP00 sample Wk- 29129 at 79.5 cm returns a date of 7659 – 7833 cal. yr BP, >4400 years older than sample Wk- 44690 extracted from BSP02 at a depth of 75 cm (3040 – 3227 cal. yr BP).

Below 95 cm (9001 – 9252 cal. yr BP) 14C dates in BSP00 show no coherency with depth (Figure 6.7B). Dates on both pollen and bulk organic material display scattered ages ranging between approximately 6033 and 8341 cal. yr BP.

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6.4.2.3 FRN02

Carbon-14 ages for different carbon fractions in FRN02 displayed high variability, with the occurrence of age reversals in some. Of the three fractions on which multiple 14C dates were obtained (macro-charcoal, pollen and SPAC), only SPAC returned sequentially older ages with depth, ranging from 983 – 1177 cal. yr BP at 48.5 cm to 11,357 – 11,814 cal. yr BP at 195.5 cm and spanning ~10,800 years (Figure 6.7C).

By comparison with SPAC, macro-charcoal ages in FRN02 varied by only ~7600 years, and of particular note, the youngest date (sample OZT919) occurred at the greatest depth (553 – 673 cal. yr BP at 198.25 cm). Pollen dates similarly showed little coherency with depth. While the upper two dates at 99.5 cm and 148 cm broadly displayed the same age-depth relationship as SPAC, the deepest date was anomalously young. The pollen dates also spanned a relatively narrow age range (~4400 years) compared to SPAC.

Of the four different carbon fractions there are three instances where dates are close to or overlap one another. At 48.5 cm SPAC returned an age of 983 – 1177 and at 50 cm macro-charcoal returned an age of 801 – 956 cal. yr BP. At 95 cm SPAC returned an age of 3637 - 3835 cal. yr BP and at 99.5 cm pollen returned an age of 3466 – 3697 cal. yr BP, although macro-charcoal from a similar depth was younger (1089 - 1276 cal. yr BP at 97 cm). Finally, at 148 cm pollen returned an age of 7666 – 7848 cal. yr BP and macro-charcoal returned an age of 7430 – 8182 cal. yr BP at 149.5 cm.

Overall, and similar to both BSP02 and BSP00, 14C ages in FRN02 were most variable at the base of the core. Dates on roots and macro-charcoal returned ages <1300 cal. yr BP, pollen 3612 – 3857 cal. yr BP and SPAC 1068 – 1271 cal. yr BP.

6.4.2.4 ELZ01

In core ELZ01 three carbon fractions were dated: macro-charcoal, pollen and SPAC. The five dates returned on SPAC exhibited consistently older ages with depth through the core ranging from 3251 – 3443 cal. yr BP at 35 cm to 14,129 – 14,811 cal. yr BP at 116 cm (Figure 6.7D).

Macro-charcoal dates also returned ages increasing with depth, although diverged from SPAC ages. For example, at 50 cm macro-charcoal was dated at 680 – 793 cal. yr BP (sample OZT914) compared to SPAC ages of 3251 – 3443 cal. yr BP and 5946 – 6265 cal. yr BP above it at 35 cm (sample OZU456) and below it at 56 cm (sample OZU457). Similarly, a macro-charcoal age of 5996 – 6304 cal. yr BP at 85.5 cm is younger than SPAC ages at 76 and 95.75 cm of 8424 – 8599 and 9686 – 10,151 cal. yr BP respectively. A 1297 - 1365 cal. yr BP age on pollen at 89 cm is younger still.

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6.4.3 Lead-210 profiles and modelled ages

Samples from the top 7 cm of BSP02 and FRN02 and the top 305 mm of ELZ01 were analysed for 210Pb activities for the purposes of building a 210Pb chronology. The results of the 210Pb analysis are presented in Figure 6.8. For simplicity, in most instances in the following text errors (2σ) are not described and median depths and activities are used.

Figure 6.8. Supported and unsupported 210Pb activities for (A) BSP02, (B) FRN02 and (C) ELZ01. The grey bar at 0 Bq/kg highlights apparent negative unsupported 210Pb activities. X- axis error bars represent the 2σ error, y-axis error bars represent the sampling depth range

In BSP02 supported 210Pb activities are both very high and variable, ranging from 484 – 950 Bq/kg. Due to these high activities and their associated errors, it is difficult to discern unsupported 210Pb activity in the core. Three samples (at 3.75, 4.75 and 6.75 cm) have apparent negative unsupported 210Pb activity. These samples have 226Ra activity in excess of 210Po activity, i.e. there is no measurable unsupported 210Pb in these samples.

The top five samples in BSP02, representing the top 2.75 cm of the core, exhibit a decay profile with depth with unsupported 210Pb activity decreasing from 153 – 11 Bq/kg, however uncertainty is high (±54 – 89 Bq/kg) (Figure 6.8A). Despite this, ages were calculated for these five samples using the CIC and CRS models. The CIC model gives ages ranging from 2011±4 – 1939±31 CE, indicating that each 5 mm sample slice represents a mean age of 12.7 years, whilst the CRS model

121 Chapter 6 gives ages ranging from 2011±2 – 1989±55 CE, with each sample representing a mean age of 19.5 years (Figure 6.9A).

In FRN02 supported 210Pb activities are also very high and variable, ranging from 181 – 487 Bq/kg and giving an apparent negative unsupported 210Pb activity for one sample from 0.25 cm. However, unsupported 210Pb activities increase with depth in the top 7 cm (from -90 – 441 Bq/kg) (Figure 6.8B) making it impossible to construct a 210Pb chronology for this core.

In ELZ01 supported 210Pb activities are high and variable, reaching >270 Bq/kg in the top 7 cm of the core though it is noteworthy that the supported 210Pb activities are generally lower in ELZ01 than in BSP02 and FRN02. Unsupported 210Pb activities for ELZ01 are much higher than in BSP02 and FRN02, and stabilise at ~400 Bq/kg below 10 cm. In addition, below 10 cm the supported and unsupported 210Pb activities are close (e.g. at 22.75 and 27.75 cm), with counting errors even overlapping for some samples (e.g. at 20.25 cm).

Unsupported 210Pb activities in ELZ01 generally decrease with depth in the top 7.75 cm of the core (from 1620 – 267 Bq/kg) (Figure 6.8C). However, there are data points which do not conform to the general relationship. Despite some uncertainty in the decay profile, particularly below 8 cm, ages were calculated for the top 7.75 cm of the core using the CIC and CRS models. The age models indicate that the upper ~7 cm of ELZ01 is <60 years old, however ages returned from the two models diverge sharply with depth (e.g. the CIC age at 7.75 cm is 1963±5 CE whilst the CRS age at the same depth is 1983±6 CE). The CIC model gives ages ranging from 2013±2 – 1963±5 CE indicating that each 5 mm sample slice represents a mean age of 3.3 years, whilst the CRS model gives ages ranging from 2014±1 – 1983±6 CE indicating a mean sample age of 2 years (Figure 6.9B). These errors for the ELZ01 210Pb chronologies are smaller than those for BSP02.

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Figure 6.9. Lead-210 derived age models for (A) BSP02 and (B) ELZ01

6.4.4 Plutonium-239+240 profiles

Plutonium-239+240 activities were analysed in the top 9 – 12 cm of cores BSP02 and ELZ01 only, since these regions of the core exhibited a general trend of decreasing unsupported 210Pb activity with depth. Results are presented in Figure 6.10. For simplicity, in most instances errors are not described in the text and median depths and activities are used.

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Activities of 230+240Pu were measured in the top 9 cm of the BSP02 core, which based on the CRS modelled 210Pb results should indicate a date between 1950 – 1850 CE, i.e. the lowest sample on which 239+240Pu was measured should pre-date atomic testing fallout. Plutonium-239+240 activities range from 0.04 – 0.13 (± 0.001 – 0.003) Bq/kg. Although these activities display a weak trend of increasing with depth, they show no discernible peak. In addition, because activities did not approach zero at 9 cm, no chronostratigraphic markers could be identified.

In the ELZ01 core 239+240Pu activities were measured in the top 12 cm, and range from 0.18 – 0.66 (± 0.003 – 0.011) Bq/kg. They display a generalised bell curve shape characteristic of fallout radionuclide deposition in sediments with a peak in activity at 8.25 cm (0.66 Bq/kg) which could possibly be attributed to the 1963 CE peak in fallout Pu in the Southern Hemisphere (UNSCEAR, 2000). However, due to the structure of the 239+240Pu activity through the core and the sampling 124 Chapter 6 frequency, the peak in the 239+240Pu may have occurred anywhere between 6.75 - 11.75 cm (Figure 6.10). The peak is also relatively broad suggesting that there may have been mixing processes at play, either through chemical migration or through physical sediment mixing from processes such as bioturbation. Despite this, the overall shape of the activity profile remains broadly as would be expected for fallout radionuclides in Australia (Longmore et al., 1983), and the presence and depth of the maximum deposition do not appear to have been affected given the relatively small proportion of the peak that is being redistributed. Because 239+240Pu activities do not reach background within the sampled range (activity ≤ measurement error) the additional chronometric anchor of the onset of atomic testing fallout in the early 1950s could not be established.

6.4.5 Ln/Tn profiles for BSP02

The BSP02 Ln/Tn profiles for quartz (BSL) and feldspar (IRSL) are shown in Figure 6.11. Values presented in the figure and following text are averaged across the three aliquots.

Figure 6.11. Quartz (BSL) and feldspar (IRSL) Ln/Tn profiles within BSP02. The organic content and photograph of this core are included for comparison 125 Chapter 6

Both the BSL and IRSL profiles show a general structure of increasing Ln/Tn with depth, however there is a region of increased variability between ~80 – 150 cm. This region of complexity also has higher BSL/IRSL ratios (2 – 7) compared to the rest of the core where ratios are predominantly ≤2, while it is also marked by relatively high variability in organic content. There is also a sharp increase in Ln/Tn values between 75.5 – 85.5 cm, concurrent with a decrease in organic content

(from ~60% to ~42%). Additionally, between ~183.5 – 215.5 cm there are two Ln/Tn values which are lower than the values surrounding them, i.e. <5 versus >5 for the sediment surrounding them.

6.5 Discussion

6.5.1 The behaviour of 210Pb and 239+240Pu in organic spring deposits and their utility for developing chronologies

Used in combination, 210Pb ages and 239+240Pu activities have the potential to provide detailed chronologies for the past 100 years of spring development. However, in BSP02 use of 239+240Pu as a chronostratigraphic marker is complex because no clear 239+240Pu activity peak conforming to peak fallout at 1963 CE could be identified. Furthermore, the onset of atmospheric nuclear weapon testing and the corresponding appearance of a 239+240Pu signal found in southern hemisphere environmental archives at ~1951 CE (Koide et al., 1979, 1985) could not be established. Activities of 239+240Pu increase slightly down profile, raising the possibility that peak 239+240Pu activity occurs below 8.25 cm (where the lowermost sample was analysed). Taking 239+240Pu activity at face value therefore implies that sediment above 8.25 cm should be younger than 1951 CE. By comparison, however, the CIC and CRS 210Pb age models indicate that the fallout period should be constrained within the top 2.75 cm of the core. Therefore there are significant discrepancies between the 210Pb and 239+240Pu systems. This is illustrated further by extrapolating these models to 8.25 cm (the maximum depth at which 239+240Pu activities were analysed) whereby they return dates of 1795 and 1004 CE respectively (Figure 6.12). This implies either the 210Pb chronologies are incorrect, which is possible as the high supported 210Pb activities are potentially convoluting the unsupported 210Pb activities, or alternatively that Black Springs may not be recording atmospheric input of Pu, or there may be mixing of Pu between stratigraphic layers.

Plutonium-239+240 activities in ELZ01 depict a peak in activity at 8.25 cm which could be attributed to the 1963CE peak in fallout Pu in the Southern Hemisphere (UNSCEAR, 2000). However, the low frequency of sampling between 6.75 – 11.75 cm may mean the precise position of the fallout signal cannot be established (the depth range over which the peak may occur is indicated by the grey box in Figure 6.10). Despite this, 239+240Pu activity in the lowermost analysed sample (at 12.25 cm) implies this depth should equate to a date younger than 1951 CE. Based upon 126 Chapter 6 the existing results the CIC 210Pb age model seems to be the best fit for the Pu fallout peak, indicating the 8.25 cm layer to have been deposited in the early 1960s. However, by comparison the CRS model attributes this layer to the 1980s (Figure 6.12). Extrapolation of the CIC and CRS modelled ages to lowest depth in which 230+240Pu activity was measured (12.25 cm) returns dates of 1935 and 1964 CE respectively, however quite clearly the activity at this layer does not suggest a first appearance of fallout, rather a midway point on the rising limb. Therefore the CIC model suggest this depth is too old by comparison to the 230+240Pu activity record, whereas the CRC model implies the depth is too young. The combination of these factors make it difficult to determine which age model is most accurate based upon the first appearance of fallout Pu.

Lead-210 activity in the spring deposits of ELZ01, FRN02 and BSP02 is very high by comparison to 210Pb fallout rates measured at locations close to the Kimberley. Annual 210Pb fallout measured at Port Headland (~1000 km south of the Kimberley) and Darwin (~650 km northwest of the study sites) (see Turekian et al., 1977) implies that spring 210Pb activity is generally higher than that attributable to atmospheric fallout alone. Lead-210 activities in ELZ01, in particular, are up to three orders of magnitude higher the estimated contribution from atmospheric fallout. Only BSP02 appears to record 210Pb activity which is consistent with (although still higher than) atmospheric fallout rates, i.e., the upper part of the spring records activities of approximately 7500 Bq/m3/yr, versus the estimated fallout contribution of 800 - 2200 Bq/m3/yr. This implies an additional source of 210Pb to the springs.

Figure 6.12. The comparison of 210Pb chronologies and 239+240Pu chronostratigraphic information for (A) BSP02 and (B) ELZ01

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Overall, despite the reasonable agreement between 210Pb ages and 239+240Pu markers in ELZ01, the behaviour of both 210Pb and 239+240Pu is not straightforward, e.g. in BSP02 there are high supported 210Pb activities and considerably lower unsupported 210Pb activities, and no agreement with 239+240Pu markers, while increasing unsupported 210Pb activities with depth in FRN02 made it impossible to construct a 210Pb chronology for this core. It should also be noted that supported 210Pb values were also relatively high in ELZ01 and in some cases resulted in apparent negative unsupported 210Pb activities.

One possible explanation for the high activities of 210Pb recorded in the spring deposits is that they represent an open system in terms of uranium behaviour. As previously described in Section 6.1.1, uranium leached from host rocks in solution in groundwater appears to be being absorbed by organic decomposition products (i.e. fulvic and humic acids) which then bind strongly with clay minerals in organic sediments (e.g. Heijnis, 1992; Heijnis and van der Plicht, 1992; Zayre et al., 2006). Consequently, uranium and its daughter products are concentrating in the organic spring deposits. This process does not require high concentrations of U-series elements in groundwater as continual groundwater input will result in progressive enrichment (e.g. Armands, 1967), which appears to be the case here. For example, 210Po and 226Ra activities in spring water filtrate (groundwater) from Black Springs, Fern Pool and Gap Springs had activities three orders of magnitude lower than activities in the residues (organic material) (Table 6.2).

Table 6.2. Polonium-210 and 226Ra activities of groundwater at Black Springs, Fern Pool and Gap Springs

210 + 226 + Filtrate Po (Bq/kg)* Ra (Bq/kg)* Black Springs <0.02 0.03±0 Fern Pool <0.02 <0.02 Gap Springs 0.03±0.01 <0.02 Residue 210Po (Bq/kg)*+ 226Ra (Bq/kg)*+ Black Springs 880±35 748±63 Fern Pool 911±38 663±57 Gap Springs 953±42 397±33 *2σ error +1 mL is equivalent to 1g

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The concentration of U-series elements in organic spring deposits is likely to be enhanced by comparison to other mires because of near-constant movement of groundwater through these systems. This explains the enrichment of 210Pb in the springs by comparison to estimated atmospheric fallout. Furthermore the convoluted relationship between supported and unsupported 210Pb activity in the springs, most notably in FRN02, implies the assumption of equilibrium between U-series elements may be violated. That is, different U-series elements may behave differently within the springs, e.g. 226Ra and 210Po from which supported and unsupported 210Pb activities are calculated.

The greater agreement between 210Pb and 239+240Pu, combined with the more conventional behaviour of 210Pb in ELZ01 by comparison to BSP02 and FRN02, may result in part from the characteristics of sediments between the springs. That is, considerably lower organic contents in ELZ01 in comparison to BSP02 and FRN02 (~35% – 40% organic content in the upper sediments of ELZ01 versus ~60% – 73% in the upper sediments of BSP02 and FRN02; see Figure 6.6) may result in fewer fulvic and humic acids in ELZ01 and therefore lower concentration of uranium. However, it is also noteworthy that the highest 210Pb activity occurred in ELZ01, suggesting caution needs to be used when interpreting these results.

Since upwelling groundwater is a characteristic of all organic spring deposits, it is likely that the problems encountered with 210Pb chronologies in this study will be experienced in similar groundwater influenced systems elsewhere. However, since regions with humid climatic conditions and periods of high rainfall favour enhanced weathering and leaching of uranium (Halbach et al., 1980) the local climate at individual organic springs, alongside local geology, hydrology and organic contents of the spring sediments themselves will influence the concentration and behaviour of U-series elements. It is therefore essential to consider these factors before attempting to build 210Pb chronologies in organic spring deposits.

6.5.2 The behaviour of different carbon fractions in organic springs

The reliability of the pollen concentrate, macro-charcoal, bulk organic and SPAC fractions for 14C dating are discussed below using down-profile characteristics of each fraction and comparisons between them (i.e. the likelihood that each 14C date accurately represents the age of sediment 14 accumulation). Additionally, the “visual” best fit between the C and Ln/Tn datasets for BSP02 is 14 depicted in Figure 6.13. This is used to compare C age-depth relationships to the Ln/Tn profile which can be assumed to reflect relative patterns in the geochronological history of sediment accumulation in the core.

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14 Figure 6.13. Quartz (BSL) and feldspar (IRSL) Ln/Tn profiles for BSP02 alongside C dates from all carbon fractions (macro-charcoal, SPAC, pollen and roots). A possible growth hiatus region is depicted by the grey line, the region of increased variability in the Ln/Tn data is indicated by shading, and the shift to lower Ln/Tn towards the base of the core is defined by brackets

Across the three dated spring systems pollen concentrate dates behave inconsistently. In FRN02 there are two cases where pollen concentrates return age ranges close to, or overlapping with other carbon fractions, suggesting that those particular dates may be reliable, although FRN02 pollen returns reversals in age below 148 cm. Aside from the two dates in FRN02, pollen concentrate dates from the cores collected in 2015 are younger than comparable dates from other carbon fractions 130 Chapter 6

(with the exception of the basal root samples), although pollen dates from BSP02 do show a coherent age-depth relationship (Figure 6.13). Additionally, despite cores BSP00 and BSP02 being collected from the same spring (Black Springs), pollen ages from the two cores display different patterns. That is, in BSP00 pollen ages (and bulk organics) below 95 cm display an erratic age- depth relationship. Consequently, 14C dates from pollen concentrate show a complex pattern in the studied springs and are assumed, in most instances, not to be reflecting their chronostratigraphic development.

Like pollen, macro-charcoal dates behave differently across the three springs. In BSP02 the age- depth profile of macro-charcoal closely follows Ln/Tn (Figure 6.13), and across the cores collected in 2015 there are three instances where macro-charcoal age ranges are close to or overlap those from other carbon fractions, suggesting these particular ages are reliable. However, in FRN02 ages on macro-charcoal are extremely convoluted with a large reversal in age returned below 149.5 cm. In BSP02 and ELZ01 macro-charcoal predominantly displays older ages with depth, indicating that dates may generally be reflecting the chronostratigraphic development of the springs. Despite this, in most instances the macro-charcoal ages are significantly different from other carbon fractions. This indicates that the macro-charcoal dates should be treated with caution.

All ages returned from SPAC following HyPy pre-treatment are older than comparable dates from other carbon fractions. There are three cases where SPAC age ranges are close to or overlap those of other carbon fractions, and in addition, SPAC is the only carbon fraction which displays consistently older ages with depth across all of the spring systems studies. Since SPAC represents the carbon fixed by pyrolysis at the time of the burning event (Ascough et al., 2009) it is an “indigenous” component of the original charcoal and is therefore likely to produce a reliable 14C date (Bird et al., 2014). Whilst there is evidence, in some cases, that SPAC can be subject to alteration and degradation (e.g. Bird et al., 2002; Ascough et al., 2010), the HyPy pre-treatment has been demonstrated to be effective in removing contaminants; e.g. it has been shown to remove >92% contamination in charcoal created at temperatures ≥400°C (Bird et al., 2014). Although a small fraction of pyrolised labile carbon may be lost during HyPy pre-treatment (Wurster et al., 2012) SPAC is therefore less likely to be subject to contamination which may affect other carbon fractions and the “original” age is likely to be better preserved. Given the consistency of SPAC ages within each core and between each spring, this fraction appears to be more reliable in describing chronostratigraphic development of the springs. The only inconsistency in the SPAC ages occurs in the bottom of BSP02 where the oldest SPAC date diverges from the general Ln/Tn profile below 183.5 cm (Figure 6.13). The reasons for this discrepancy are discussed in the following sections.

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6.5.3 Sources of 14C anomalies

As discussed in Section 6.1.1, there are a number of potential processes that could be affecting 14C ages in the studied springs. One possibility is that the chronostratigraphic integrity of the springs is compromised by mixing and overturning. An alternative is that various carbon fractions are contaminated within the springs due to translocation of fractions within the spring profiles, biological activity within the spring sediments, or incorporation of young or old carbon.

6.5.3.1 The influence of mixing, overturning and erosion on spring chronologies

Processes such as mixing, overturning or erosion could affect the chronostratigraphic integrity of the springs. In the case of highly organic springs, these processes are not often apparent in the sedimentology of the deposit. For this reason the luminescence properties of core BSP02 were analysed by measuring the Ln/Tn signal through that core (Figure 6.11). Although not providing ages, the Ln/Tn profile provides an indication of the stratigraphy and age structure of the core. Consequently, overturning or hiatuses in the growth of the spring would be recorded in reversals or step changes in the Ln/Tn ratio. In BSP02 the Ln/Tn profiles exhibit a generalised trend of increasing ratios with depth. This implies that the core has predominantly maintained its chronostratigraphic integrity with no large scale internal mixing of the deposit.

However, the Ln/Tn indicates there are some potential disturbances. The sharp increase in Ln/Tn values between 75.5 – 85.5 cm is indicative of either an unconformity, or a change in mound growth. This change is otherwise undetected in other parameters (e.g. colour and texture). An unconformity could result from removal of material e.g. deflation during periods of increased aridity and sediment desiccation, or scouring during periods of increased precipitation. Alternatively, this may represent a hiatus in spring growth or a decrease in spring productivity, however the latter scenario is at odds with an increase in core organic content above 80 cm (Figure 6.11).

Another region of potential spring disturbance can be recognised by high variability in the Ln/Tn ratios between ~80 – 150 cm. In that section of the core the Ln/Tn ratios do not consistently increase with depth, while in addition the BSL and IRSL signals diverge from one another (grey box in Figure 6.13). This could represent a partially mixed region of the core by processes such as cracking, self-mulching, bioturbation, slumping or changes in vent position. Divergence in the BSL and IRSL signals may also imply material of a different origin of quartz (BSL) versus feldspars (IRSL) and/or a different depositional history given the greater sensitivity of quartz to bleaching, e.g. more local sediment rather than long-range dust input (e.g. McGowan, et al., 2012).

132 Chapter 6

Alternatively, these differences could reflect dose rate variations, e.g. corresponding with variable U load associated with integration of groundwater and fluctuating organic content (Figure 6.11). Variable dose rates are more likely to have influenced the region between 190 - 220 cm (as indicated on Figure 6.13) as this region represents the transition between the more organic section of the core and the silty clay (Figure 6.6) in which dose rate fluctuations are most likely due to hydrologic variability.

Despite some minor potential complexity in the chronostratigraphy as indicated by the Ln/Tn data, the overall impression is that the chronostratigraphy is largely intact and is therefore unlikely that severe complications of spring stratigraphy are responsible for the erratic 14C age-depth relationships frequently observed. However, the divergence in ages between different carbon fractions may, in some cases, be attributed to this minor complexity. This is discussed in more detail in the sections that follow.

6.5.3.2 The effect of roots on 14C ages

As described above in Section 6.3.1 cores BSP02, FRN02 and ELZ01 contained abundant root fragments throughout. The prevalence of roots throughout organic spring deposits is unsurprising since these environments support enhanced plant growth, often with deep rooted vegetation by comparison to the surrounding landscape (Scott and Vogel, 1983). For instance, Phragmites is often found growing across organic springs and can have root and rhizome penetration >1.8 m (Granholm and Chester, 1994). Although both sieving and heavy liquid separation were used to remove these, root fragments were still observed under light microscopy in the <150 µm size pollen fraction retained for dating.

The presence of roots affecting 14C ages has been noted in numerous studies, including in Chapter 5. As previously mentioned, initial 14C ages at Florisbad Spring, South Africa were assumed to be influenced by root contamination (Kuman and Clarke, 1986). Efforts to remove root fragments (by hand) from bulk organic 14C samples resulted in different ages and, importantly, a consistent stratigraphic chronology at this site (Scott and Nyakale, 2002) implying that roots were a source of contamination. Similarly, a microscopic search of spring sediments from Rietvlei in South Africa revealed that abundant minute rootlets were at depths concurrent with anomalous 14C dates (Scott and Vogel, 1983). Roots have therefore been frequently credited with contaminating 14C dates from organic spring deposits in a variety of global locations (e.g. Chapter 5; Butzer, 1984a, 1984b; Kuman and Clarke, 1986; van de Geer, 1986; Boyd, 1990b; Scott et al., 2003; Field et al., 2017).

133 Chapter 6

The ages returned by the roots in BSP02 and FRN02 were considerably younger than corresponding dates from other carbon fractions (with the exception of macro-charcoal in FRN02 which is younger than the roots for reasons discussed in Section 6.5.3.3). Ages on roots at the base of BSP02 also diverged from the Ln/Tn profile (Figure 6.13) suggesting that they do not reflect the true age of sediment accumulation.

As described in Section 6.1.1 roots can facilitate the transport of young carbon into older stratigraphic units via a number of processes. Consequently the pollen concentrate ages, which were consistently younger than other carbon fractions, are considered likely to be contaminated by the introduction of young carbon from root fragments retained within the pollen fraction. The ages on bulk organics may be similarly affected. Furthermore, roots are able to penetrate large charcoal fragments (Harkness et al., 1994) so it is possible that minute fragments also affected the macro- charcoal ages.

In the studied springs, root contamination is likely to be most severe in the deepest stratigraphic units of organic spring deposits since those roots have been present for longer periods of time and may be decomposed, making them particularly difficult to differentiate from the surrounding organic sediment (Scott et al., 2003). In BSP02, BSP00 and FRN02 the most variable dates are in the lower stratigraphic units suggesting that this is the case.

6.5.3.3 Groundwater effects on 14C ages

Inspection of charcoal fragments from the studied springs by optical microscopy revealed that they were sometimes soft and coated with a light-coloured waxy residue, i.e. they lacked the vitreous lustre typical of charcoal. This was particularly the case for FRN02. Subsequent examination by an SEM equipped with EDXA further revealed charcoal fragments in FRN02 generally had a degraded structure by comparison to those in cores BSP02 and ELZ01 (Figure 6.14), although this was not ubiquitous in all charcoal fragments recovered from FRN02 (see Figure 6.14G). EDXA showed that the altered charcoal fragments from FRN02 contain a more complex chemical structure, most notably with large concentrations of aluminium, phosphorus, silicon and sodium (Figure 6.15). This was most apparent in two dated samples from FRN02 (OZT917 and OZT919 - Figure 6.14F and Figure 6.14H respectively, and Figure 6.15). In these samples C comprised <30% of OZT917 and <40% of OZT919, while the fragments contained inclusions of Al (>7%), Si (4 - 8%) and P (1 - 5%). By contrast, charcoal from BSP02 appeared relatively unaltered and contained higher concentrations of C (57 – 67%), with only minor concentrations of Si and S present (<2%). Other charcoal samples from ELZ01 (OZT914 and OZT915) and FRN02 (OZT918) showed no obvious visual alteration (Figure 6.14I and Figure 6.14G respectively), but still contained relatively high 134 Chapter 6 concentrations of Na (3% in OZT914), Si (2% in OZT918), P (~1% in all), and Al (4% in OZT915) (Figure 6.15) implying some possible minor alteration.

BSP02 BSP02 A B BSP02 C

D BSP02 E FRN02 F FRN02

G FRN02 H FRN02 I ELZ01

ELZ01 FRN02 BSP02 J K L

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Figure 6.15. Elemental composition (% by weight) of charcoal fragments from macro- charcoal 14C samples in Kimberley springs. Samples are plotted alongside their calibrated ages (shown as grey bars) and depth-sequences (shown as orange lines) for comparison

Consistent with the presence of more altered charcoal, 14C ages on macro-charcoal from FRN02 returned similar ages from different depths which were much younger than ages returned on other carbon fractions. In particular, sample OZT919 was visually degraded and contained high concentrations of other elements. It returned a pronounced reversal in age (Figure 6.15) in comparison to all other 14C ages from the core. The less altered charcoal in sample OZT918 returned an age close to that of SPAC (sample OZU460). Alteration of charcoal has previously been reported at Nauwaliabila I in the Northern Territory (Bird et al., 2002). Optical microscopy, SEM and EDXA investigation in that case also revealed that charcoal fragments were soft, heavily coated by iron oxides and clays and had severely degraded internal structures and high abundances of elements other than carbon (e.g. iron, aluminium and oxygen) (Bird et al., 2002). This was concluded to result from ongoing replacement of the original charcoal by iron and aluminium oxides and oxihydroxides. Subsequent macro-charcoal 14C dates from Nauwaliabila I were considered to be inconsistent with the likely chronostratigraphy (Bird et al., 2002).

As described in Section 6.1.1, alteration of charcoal in high weathering environments, such as northern Australia, is facilitated by the large surface area and porous nature of charcoal. This

136 Chapter 6 enables the in-situ contamination by young carbon through the adsorption of organic or inorganic compounds which can move in solution through the sediment (Bird, 2007), or through oxidative processes (Cohen-Ofri et al., 2006) mediated by microbial activity and photo-oxidation (particularly in coarser sediment matrixes) (Bird et al., 1999). Since water tables in springs typically fluctuate in response to climatic variability (Scott, 2016) charcoal may be altered by these processes in organic spring deposits. It is therefore likely that the charcoal alteration observed in the Kimberley springs has affected the 14C ages, as evidenced by younger macro-charcoal ages in comparison to SPAC ages in FRN02 and ELZ01. Because charcoal will also comprise a portion of any bulk organic samples and can be broken down into finer fractions (Walker, 2005; Bird, 2007) it is likely that it is also present in pollen concentrate (e.g. Mensing and Southon, 1999).

At the Nauwaliabila I site in the Northern Territory altered charcoal occurred alongside authigenic pisolites and altered quartzite fragments. This implied that charcoal alteration resulted from water table fluctuations (Bird et al., 2002). It is likely that the same mechanism was responsible for the charcoal alteration observed in FRN02 and ELZ01. The TiO/Al2O3 concretions in FRN02 are indicative of water table variations, with similar concretions observed in dehydrating conditions (Sherman, 1952). That these are only present in FRN02 indicates that groundwater fluctuations have been most pronounced at this site, again consistent with the greatest degree of charcoal alteration.

6.5.3.4 Allochthonous transport of old charcoal

As previously discussed, 14C dates on pollen concentrate, bulk organics and even macro-charcoal are likely to have been compromised by additions of young carbon. It is also possible that old carbon may be reintroduced by, for example, aeolian and alluvial deposition. This potentially 14 affects the lowest SPAC C date in BSP02, where this age is distinct from the Ln/Tn profile (Figure 6.13). The sediments of the lower units of BSP02 consist of less organic material (Section 6.3.1), deposited early in the development of the spring predominantly by alluvial (and to a lesser extent, aeolian) deposition (e.g. Field et al., 2017). The difference between this SPAC age (sample

OZU455) and the Ln/Tn ratios in the lower stratigraphic unit may therefore reflect the incorporation of “old” charcoal remobilised from the surrounding landscape and transported into the spring largely by alluvial processes. There is also a risk that finer “old” charcoal may be incorporated via aeolian processes at any stage of spring growth. Since the SPAC was extracted by HyPy from bulk sediment samples there was no way to differentiate whether it is derived from macroscopic or microscopic charcoal (the latter reflecting the fine fraction). However, there are two results where SPAC 14C age ranges are close to or overlap macro-charcoal 14C dates, suggesting that the SPAC in

137 Chapter 6 all but the deepest stratigraphic units (e.g. BSP02) is relatively uncompromised by “old” fine fractions.

6.5.4 The feasibility of different carbon fractions for building reliable 14C chronologies in organic spring deposits

Results presented here show that in organic spring deposits there are a number of processes which can affect different carbon fractions. There is therefore value in dating multiple fractions to both refine the chronology of these archives and to understand how processes within spring environments can affect 14C results.

In these settings root fragments are likely to comprise part of any bulk sediment or pollen concentrate (and potentially even macro-charcoal) sample submitted for 14C dating. Very fine rootlets cannot be easily separated from these carbon fractions via chemical or physical pre- treatment (e.g. density separation or acid digestion) without also removing the target material for dating. Whilst it appears that roots can be removed from organic spring deposits by hand with successful results (e.g. Scott and Nyakale, 2002), removing root fragments in this way is not always possible since the extremely time consuming nature of this task would make it impractical for most studies. It is also likely that very small or light coloured fragments may be missed, particularly in deeper stratigraphic units where roots may be indistinguishable from the surrounding matrix (Scott et al., 2003).

In organic spring deposits macro-charcoal can be contaminated by organic/inorganic compounds and oxidation via fluctuations in groundwater, a process inherent in spring systems (Scott et al., 2016), however these contaminants often appear impossible to remove by AAA pre-treatments (e.g. Gillespie et al., 1992; Harkness et al., 1994; Higham et al., 2009a, 2009b), or potentially even more aggressive oxidation stepped combustion techniques such as ABOX-SC (e.g. Bird et al., 2002). It is therefore essential to assess the suitability of charcoal prior to 14C analysis since ages will be unreliable where there is post-depositional alteration. It is important to note that this alteration is not always visually apparent and that SEM micrographs alone are insufficient to discern it. Therefore EDXA or similar should also be used to assess the suitability of the charcoal fraction prior to use, however such investigation may prove too time consuming for most studies. Given the abundance of roots throughout organic spring deposits, even when there is no evidence of alteration, charcoal ages should be interpreted with caution as it is possible that roots may have penetrated charcoal fragments targeted for dating (Harkness et al., 1994). As charcoal is likely to comprise part of bulk organic and pollen concentrate samples, where alteration exists this will contribute to inaccuracies in 14C dates from these fractions. 138 Chapter 6

Overall, SPAC isolated by the HyPy pre-treatment is the most successful means for removing contamination introduced by roots, groundwater fluctuations and associated weathering that would otherwise result in erroneous ages. These results presented from Black Springs and Fern Pool, along with those from other spring studies, suggest that the effects of carbon contamination in springs becomes more pronounced with time, that is dates from the bottom lower sections of springs on different carbon fractions show the greatest degree of variability (Figure 6.2, Figure 6.3 and Figure 6.7). The implication of this has been that while, in some cases, it has been possible to extract some palaeoenvironmental information from proxy data sets within springs, developing reliable chronologies for the lower sections of springs has been problematic (e.g. Butzer 1984a, 1984b; van de Geer et al., 1986; Scott, 1987; Macphail et al., 1999; Scott et al., 2003; Dobrowolski et al., 2012; Fluin et al., 2013; Mazurek et al., 2014; Field et al., 2017). Consequently, in some studies palaeoenvironmental reconstructions have only been produced for the top section of springs (e.g. McGowan et al., 2012), while in other studies (e.g. Field et al., 2017) age models, based on reliable ages from the top sections of springs, have been extrapolated to older sections (see Chapter 5). These approaches have obvious limitations in terms of record length and reliability. The results presented here suggest HyPy provides a means of reliably building chronologies within complex spring environments, thereby placing environmental and climatic changes on more secure timescales throughout the entire spring sedimentary record. HyPy as a technique is also advantageous as it is rapid and efficient, requiring no prior or additional pre-treatments (physical or chemical) prior to dating, that is, following HyPy the sample can be converted directly to CO2 (Ascough et al., 2010). Furthermore, HyPy has a high degree of measurement precision (Ascough et al., 2009; Meredith et al., 2012). However, in juvenile springs SPAC may be contaminated by “old” allochthonous charcoal.

6.6 Conclusions

This study demonstrates that in complex hydro-geological settings such as springs, there is a need to understand the behaviour of different components targeted for dating. It also shows the value of utilising multiple radionuclides for understanding spring behaviour and developing accurate chronologies for their sediments. This is important since, despite the complexity of organic spring deposits as highlighted by this study, they are critical palaeoenvironmental archives in many settings. Therefore, developing accurate geochronology is crucial for understanding past environments.

This study reveals that in organic spring deposits there are multiple sources of contamination which can convolute 14C chronologies, and highlights that not one single carbon fraction appears to be

139 Chapter 6 universally reliable. Pollen concentrate, bulk organic and macro-charcoal fractions are unsuitable for obtaining accurate 14C dates in these settings due to contamination introduced by roots and groundwater fluctuations. In some cases, macro-charcoal pre-treated with the AAA technique may be appropriate where it has not undergone post-depositional alteration, although it is essential that charcoal fragments are examined for contamination. However, groundwater fluctuations inherent in spring environments limit the use of this approach, and the investigation of macro-charcoal is likely to be too time consuming to be practical in most cases. Alternatively, the HyPy pre-treatment methodology is a rapid, effective method for the removal of several primary sources of geochronological complexity, and can isolate unaltered SPAC from charcoal likely giving reliable 14C dates in deposits of well-developed organic springs. There is a risk, however that “old” carbon may be incorporated in juvenile spring sediments, and that a small fraction of the labile carbon component may also be pyrolysed during HyPy treatment. The former is not an issue specific to the HyPy pre-treatment methodology but rather, to the spring environment and will affect all age determinations using 14C.

Providing age control for recent spring sediments via 210Pb methodologies may prove more difficult due to post-burial enrichment by uranium which is common to organic sediments in open systems such as springs. The degree of enrichment is likely to vary between individual springs based on organic content of the sediments, local hydrological and climatic conditions, and geology. These parameters should be taken into account when considering the use of 210Pb analysis for age determination.

It is therefore recommended that a combination of methods are used to build chronologies for organic spring deposits including HyPy to isolate SPAC for 14C analysis, circumstantial evidence, 210 239+240 and auxiliary datasets such as Pb, Pu and Ln/Tn. The ability to construct reliable chronologies in these settings will facilitate the correct interpretation of palaeoenvironmental, palaeoclimatic, archaeological and palaeontological records, including those presented in Chapter 7. This is of particular importance in arid and semi-arid environments which contain few sites other than organic springs suitable for building continuous records of environmental and climatic change. Although this study pertains to springs, the contamination pathways described here are not exclusive to these systems and these results are likely widely applicable to other settings, .e.g. swamps or marshes experiencing significant seasonal changes in hydrology and deep root growth. Accordingly, this also highlights that caution should be exercised in the interpretation of age models from similar sites and environmental settings where pollen, charcoal and bulk organic samples have been used for 14C dating.

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7 Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years

This chapter is reproduced from the following submitted manuscript:

Field, E.; Tyler, J., Gadd, P., Moss, P., McGowan, H., Marx, S., in review. Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years. Quaternary Science Reviews.

The outcomes of Chapters 5 and 6 demonstrated that organic spring deposits are valuable archives of palaeoenvironmental change since they contain proxies amenable to this research and can be reliably dated. This chapter uses the chronological results presented in Chapter 6 to address research objective 4, which facilitates the development of new palaeoenvironmental records spanning the last ~14,500 years since the LGIT. Since it is difficult to disentangle regional-scale changes from local idiosyncracies within a single site, such as in the Black Springs record presented in Chapter 5, this chapter addresses research objective 7 by comparing three new palaeoenvironmental records from three springs (cores BSP02, FRN02 and ELZ01). This comparison includes the use of statistical analyses such as PCA and MCEOF analysis which enable patterns of genuine regional- scale change (i.e. >1000s km2) to be detected. These regional interpretations are then linked to potential drivers of climatic variability to address research objective 8.

7.1 Introduction

Black Springs, an organic spring deposit located in the North Kimberley Bioregion (Government of Western Australia, 2011; Figure 7.1), has been previously analysed for pollen, micro-charcoal, trace element geochemistry, organic content and humification, providing an impression of monsoon variability over the last ~15,000 years (Chapter 5; McGowan et al., 2012; Field et al., 2017). Changes in a single record from one location, such as this, are often assumed to be representative of a wider spatial area, although some multi-site comparisons of proxy records from similar archives in the same geographic area have shown limited correspondence suggesting this is not always the case (e.g. Schmieder et al., 2011; Moss et al., 2013; Roberts et al., 2015). This is problematic for reliably inferring climatic and environmental changes across a wider area, and as a result palaeoclimate research is increasingly moving away from the single-site approach (Tyler et al., 2015). Whilst Black Springs has yielded valuable climate information, it remains unclear if it is

141 Chapter 7 recording a regional climate signal, or whether it is reflecting local spring dynamics or microclimate.

It is possible to partition changes in proxies recorded in palaeoenvironmental records between regional and local factors, and test the issue of replicability by using records from multiple sites within close proximity (e.g. Schmieder et al., 2011; Mills et al., 2014; Roberts et al., 2015). Agreement between sites may be hypothesised to reflect a regional-scale signal (i.e. reflecting broad changes on the scale of >1000s km2), whereas a lack of correspondence is assumed to reflect a component of local variability (i.e. 10s – 100s km2) (Roberts et al., 2015; Tyler et al., 2015). It is worth noting that apparent inter-site differences may also be a result of chronological imprecision, or relative preservation (Payne and Blackford, 2008; Roberts et al., 2015). This can be particularly problematic in tropical and monsoonal environments such as the Kimberley, since these climatic settings generally restrict the accumulation of sediment with an annual resolution. Geochronological techniques such as 14C, OSL and 210Pb dating are therefore commonly used in the construction of age-depth models for palaeoclimate records from these regions. However, the compounding analytical and calibration errors from these methods can introduce large temporal uncertainties making it difficult to identify the precise timing of events and shared trends between sites (Anchukaitis and Tierney, 2012; Tierney et al., 2013). Moreover the application of standard dating methodologies has been shown to be problematic in springs due to complex hydrological, geomorphic and biological conditions (Chapter 6; Field et al., 2018).

In order to discern regional-scale climate and environmental change in the Kimberley since the late Pleistocene, a multi-proxy, multi-site approach is adopted, and account for age uncertainty to determine genuine inter-site coherency. Records from three organic springs spanning a ~100 km transect along a broadly north-south transect are utilised, and a new record from Black Springs developed (Chapter 5; McGowan et al., 2012; Field et al., 2017). Sediment cores from the springs have been analysed for multiple palaeoecological and geochemical proxies, including pollen, micro- charcoal, NPPs, and elemental geochemistry (Itrax µXRF core scanning).

7.2 Study sites

Three organic spring sites within the Kimberley region of northwest Australia were selected for analysis and comparison: Black Springs (15.633°S, 126.389°E), Fern Pool (15.937°S, 126.284°E), and Gap Springs (16.404°S, 126.134°E) (Figure 7.1) (see Section 2.5 for additional site information).

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As outlined in Section 2.5, the three studied organic springs are all located on the Kimberley Plateau which covers approximately 113,000 km2 (Tille, 2006) (Figure 7.1A). The dominant lithology of the Kimberley Plateau are the Kimberley Group sandstones (Wende, 1997; Brocx and Semeniuk, 2011), although siltstones, shales and mudstones are also present (Tille, 2006) (Figure 7.1B). Surface lateritic duricrusts have also developed in some areas associated with basalts and shale-sandstones (Tille, 2006). The groundwater feeding the studied springs is derived from local aquifers of low to moderate productivity stored within the Kimberley Group sandstones, distinct from the extensive, productive aquifers of the Canning Basin and Bonaparte Basin to the west and east (Brodie et al., 1998) (Figure 7.1A). Recharge in such fractured rock aquifers is typically localised and immediate (Geoscience Australia, 2017) (refer to Section 2.2).

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Figure 7.1. Location of the three springs (BSP02, FRN02, ELZ01) in relation to: (A) physiographical divisions adapted from Wende (1997) and hydrogeological divisions adapted from Brodie et al. (1998). (B) Simplified geological divisions of the Kimberley Plateau , indicating the location of major lithological units including the Kimberley Sandstone (KLS; medium grey), Carson Volcanics (CV; dark grey), Warton Sandstone (WS; white) and Pentecost Sandstone (PS; light grey) adapted from Brocx and Semeniuk (2011). (C) Overview map of northern Australia, location of panels (A) and (B) are indicated by the black square

As discussed in Section 2.4, the Kimberley’s climate is monsoonal, with precipitation predominantly derived from tropical cyclones and the IASM during the Austral summer (December – March). Specific climate data for the three study sites is detailed in Section 2.5, which indicates that average annual rainfall and temperature data is not uniform across the study region (e.g. Black Springs receives the greatest precipitation of the three sites whilst Gap Springs receives the least).

The three springs are located within a Tropical Eucalypt Woodland/Grassland environment (MVG 12) (refer to Section 2.5) which consists of a Eucalypt/Corymbia canopy with (tall) grass understorey (Department of the Environment and Water Resources, 2007). The springs themselves are heavily vegetated, as a result of the currently largely permanently wet conditions. P. karka (a perennial aquatic grass), Cyperaceae species (sedges), Typha, Melaleuca and P. spiralis are common to all, whereas Black Springs is also covered by Colocasia esculenta and monsoon vine thicket taxa including Ficus and T. timon (Department of Environment and Conservation, 2012 and field observations). P. congestus and O. basilicum/B. polystachyon are found at Fern Pool, and B. dentata is prevalent at Gap Springs (Department of Environment and Conservation, 2012 and field observations) (see Section 2.5). Subsequent decomposition of this dense vegetation at each spring has enabled the accumulation of organic material, with Black Springs and Fern Pool forming topographically distinct mounds of organic detritus whereas Gap Springs is less protuberant. Fern Pool is also distinct from the other two springs in that there are several mounds in close proximity (see Section 2.5).

7.3 Materials and methods

7.3.1 Sample collection and description

All three sites were cored using a 0.5 m long Russian D-section corer in June, 2015. A 2.44 m core was collected from Black Springs (BSP02), a 2.04 m core was collected from Fern Pool (FRN02), and a 1.36 m core was collected from Gap Springs (ELZ01). An older/shorter 1.68 m core (BSP00) was obtained from Black Springs in 2005 and is described in Chapter 5, McGowan et al. (2012) and

144 Chapter 7

Field et al. (2017). Cores were scanned at ANSTO with the Itrax µXRF core scanner, and subsequently sub-sampled at 5 mm resolution. Stratigraphic techniques used to describe the cores included field-texture analysis of grain size, and LOI following Dean (1974) and Heiri et al. (2001), with full results presented in Chapter 6 and Field et al. (2018), and summarised here in Figure 7.3 - Figure 7.5 for the purposes of comparison.

7.3.2 Geochronology

A detailed study of the geochronology of BSP02, FRN02 and ELZ01 is presented in Chapter 6 and Field et al. (2018), in which the behaviour of different dating systems was examined alongside an assessment of the stability of different carbon fractions in each site (pollen concentrate, macro- charcoal, roots and stable polycyclic aromatic carbon (SPAC)). It was concluded that 14C ages determined on SPAC isolated by hydrogen pyrolysis (HyPy) pre-treatment were largely devoid of the contamination which had influenced ages on other carbon fractions. Chronological control for the uppermost sediments was also attempted using 210Pb and 239+240Pu as geochronological fallout markers, however, the behaviour of 210Pb in each core was not straightforward, there was considerable uncertainty associated with the 210Pb ages, and there was a lack of agreement with 239+240Pu markers (see Field et al., 2018).

Consequently, in this study age models were developed using only 14C ages from SPAC, or where two or more 14C dates from different fractions are in agreement and in line with SPAC ages (Table 7.1). Conventional 14C ages were calibrated to calendar years before present (cal. yr BP) using OxCal V4.2.4. (Bronk Ramsey, 2013) and SHCal13 (Hogg et al., 2013) with 0 cal yr BP representing 1950 A.D. Bayesian age-depth models were constructed for each site using Bacon 2.2 (Blaauw and Christen, 2011) in R (R Core Team, 2013), using 10,200 age iterations with the first 200 iterations removed, and the 14C dates presented in Table 7.1. To account for age uncertainty, we iteratively calculate a further 10,000 age-depth models for each dataset record in R (R Core Team, 2013).

145 Chapter 7

7.3.3 Geochemical analysis

The three cores were scanned using the Itrax µXRF scanner at ANSTO, with a chromium (Cr) target tube. The operating conditions for X-radiograph was 45 - 55 kV, 30 mA, and for XRF scans it was set at 30 kV and 55 mA with a 20 second exposure time for each step. Micro-XRF profiles for 37 elements at a 1 mm resolution were produced for each core (Al, Ar, Ba, Bi, Br, Ca, Ce, Cl, Cs, Cu, Dy, Fe, Ge, Hf, K, La, Mg, Mn, Nb, Nd, Ni, P, Pb, Pm, Pr, Rb, S, Sc, Se, Si, Sr, Ta, Ti, V, Y, Zn, Zr). Significant variations in total counts per second occurred at core ends or in sections of unconsolidated material (e.g. sand at the base of ELZ01). In order to present data primarily reflective of environmental change, artefacts introduced by these count variations were removed (e.g. Kylander et al., 2011; Mackenzie et al., 2016). Of the 37 elements, those that were very noisy (no coherent trend) or those with low counts per second (>5% of the data recording 0 counts) were not considered to be statistically consistent and were removed from the dataset (e.g. Saez et al., 2009).

Itrax µXRF scanners are relatively insensitive to organic sediment which will have the effect of diluting measurable components (the closed-sum effect) (Löwemark et al., 2010). Homogenous deposits consisting of fine grained sediments which are more similar in nature to dry, powdered, homogenised samples used in conventional XRF analysis, are therefore most suitable for µXRF scanning (e.g. Haug et al., 2001). However, there are significant changes in composition within the three cores used in this study (from inorganic to organic rich) which carries a risk that, to an extent, elemental intensities will mirror down-core changes in organic content. It has been demonstrated that the use of log-ratios and centred log-ratios of element intensities generated by µXRF scanning are linear functions of log ratios of absolute element concentrations, and therefore provide a statistically robust interpretable signal of relative changes in chemical composition (Weltje and Tjalligii, 2008). Elemental intensities (counts) in the reduced datasets for BSP02, FRN02 and ELZ01 were therefore converted to centred natural logarithms following Weltje and Tjalligii (2008) following which they were utilised for qualitative interpretation.

The selection of elements and ratios for determination of palaeoenvironmental conditions (i.e. Ti, Fe, K, Si, Ca, Si/Ti, Mn/Ti and Cr Inc/Coh (incoherent/coherent scattering) which is the scattering of radiation emitted by the Cr target tube and may be a qualitative measure of organic content) was made based on the behaviour of these elements and their value for determining palaeoenvironmental conditions, the consistency of counts within the core, as well as their use in other similar settings (Margalef et al., 2013; Chawchai et al., 2015; Burrows et al., 2016).

146 Chapter 7

Correlation matrices were performed on the eight key parameters (centred log-ratios) in order to explore the strength of relationships between different variables.

To support the environmental interpretations made from the Itrax µXRF data in Section 7.5.1, representative samples from BSP02 were examined by SEM with element distributions obtained by EDXA on a Hitachi TM3030 desktop SEM with Bruker EDS at The University of Queensland, following digestion of organic material in these samples by 30% H2O2.

7.3.4 Pollen, NPP and micro-charcoal analysis

Samples for pollen, NPPs and micro-charcoal analysis were taken (where possible) every 10 cm in BSP02 (N=25) and FRN02 (N=21), and every 5 cm in ELZ01 (N=26). Samples were prepared for analysis following Moss (2013), with this method described in Section 5.3.3.

Samples were mounted in C3H8O3 on slides for identification and counted with light microscopy at ×400 magnification. Palynomorph identification was aided by the Australasian Pollen and Spore Atlas (APSA Members, 2007), whilst NPP identification was aided by Scott (1992), Carrión and Navarro (2002) and Medeanic and Silva (2010). Pollen counts consisted of 300 grains or two completely counted slides, with counts expressed as percentages of the total pollen sum (local pollen sum composed of pteridophytes, spring and wetland taxa; regional pollen sum composed of grass and tropical savanna taxa). The charcoal counts consisted of all black angular pieces >5 µm counted across three transects. Lycopodium clavatum, an exotic marker spike, was added to samples to enable calculations of pollen, micro-charcoal and NPP accumulation rates (expressed per cm3). Delineation of pollen assemblage zones were guided by CONISS analysis (Grimm, 1987) on taxa included in the local pollen sum since these are most responsive to changes in spring hydrology. Pollen, NPP and micro-charcoal data was collated and plotted with Tilia (Grimm, 1991) and TGView (Grimm, 2004). Pollen diagrams exclude taxa with low values (less than 5%). This analysis was undertaken at a higher temporal resolution for BSP00, with the results presented in Section 5.4.3 and Field et al. (2017), and similarities in taxa observed between BSP00 and BSP02.

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7.3.5 Statistical methods

7.3.5.1 Principal Components Analysis (PCA)

In order to summarise patterns of change in three datasets (geochemistry, pollen, and NPPs), PCA was undertaken on each in CANOCO 4.54 (ter Braak and Šmilauer, 2002). Principal Components Analysis was selected following assessment for suitability with DCA with detrending by segments following ter Braak and Prentice (1988). Principal Components Analysis was undertaken on: a reduced Itrax µXRF dataset (noisy elements or those with low counts removed as described above) with counts corrected to the sum of total counts; the full pollen dataset; and the full NPP dataset. Principal Component Analysis axis 1 scores are plotted with age uncertainty in Figure 7.10.

7.3.5.2 Monte Carlo empirical orthogonal function (MCEOF) analysis

Empirical orthogonal functions (EOFs) can identify shared coherency between multiple sites and provide evidence for regional-scale climate change compared to local idiosyncrasies (Tyler et al., 2015). Monte Carlo iterative age modelling within EOFs has also been used to take into account age uncertainty which can be inherent in palaeoenvironmental records (e.g. Shakun and Carlson, 2010; Anchukaitis and Tierney, 2012; Tyler et al., 2015). Monte Carlo empirical orthogonal function analysis therefore provides a means to empirically and objectively assess the synchronicity of changes observed in different time-uncertain palaeoenvironmental records by isolating dominant modes of regional variability (i.e. highlighting trends that are reliably shared between sites).

Monte Carlo empirical orthogonal function (MCEOF) analysis was applied to the three springs used in this study, following Anchukaitis and Tierney (2012) using code for R (R Core Team, 2013) developed by Tyler et al. (2015) and Falster et al. (2018). We further developed this approach through the application of Data Interpolating EOF (DINEOF) to compensate for missing data following Beckers and Rixen (2003). DINEOF was implemented using the sinkr package for R (Marc Taylor; https://github.com/marchtaylor/sinkr). For the Si/Ti record, 10,000 age model iterations were taken from the Bacon age model output. For the Pseudoschizaea record (a NPP indicative of desiccation, drought, oxidation and warmer climates associated with seasonal drying (Scott, 1992; Carrión and Navarro, 2002; Table 7.3)), due to the smaller number of sample points and additional time taken to run DINEOF, 2000 age model iterations were taken from the Bacon age model output. For each age model iteration the palaeoenvironmental data of interest was interpolated and resampled at 100 year intervals between 0 – 14,500 cal. yr BP (the approximate basal age of at least two of the three studied cores) to generate bootstrapped ensembles of possible proxy records. Empirical orthogonal function loadings and EOF time series expansions were each

148 Chapter 7 defined by one of the age-depth models. Principal Components Analysis was performed with each of these ensembles to generate EOFs from which the median, 68% and 95% confidence intervals were derived as representative of the between-site pattern and effect of chronological uncertainty. The significance of the EOFs was tested by comparing a screeplot of variance explained against a random distribution based upon a broken stick model, following Bennett (1996) and Tyler et al., (2015).

Following visual comparison of the PCA axis 1 scores (Figure 7.10) it was evident that, within age uncertainty, the local Itrax µXRF and NPP datasets exhibited similar patterns of change at the three sites whilst the pollen did not (Section 7.4.4.1). Monte Carlo empirical orthogonal function analysis is therefore only applied to the Itrax µXRF and NPP datasets, synthesizing one variable from each. Whilst the selection of one representative variable from each dataset is subjective and may lead to the loss of some relevant information (Tyler et al., 2015), in this instance the similarity of the sedimentary environments and proxy types between sites justified a guided approach based on proxy interpretation. Si/Ti ratios and Pseudoschizaea accumulation rates were therefore selected from the Itrax µXRF and NPP datasets respectively to assess regional patterns of change in site moisture from the late Quaternary to present, grounded by understanding of these sites (see Section 7.5) as well as previous research which has used these proxies as indicators of changes in site hydrology in other locations (e.g. Scott, 1992; Carrión and Navarro, 2002; Brown et al., 2007; Stansell et al., 2010; Balascio et al., 2011; Brown, 2011; Burnett et al., 2011; Kylander et al., 2011; Martin-Puertas et al., 2012; Melles et al., 2012).

7.4 Results

7.4.1 Geochronology

Carbon-14 dates used in the construction of the core chronologies (age models) are presented in Table 7.1. The age model for BSP02 is based on a total of five AMS 14C dates on SPAC (N=4) and macro-charcoal (N=1); the age model for FRN02 is based on a total of seven AMS 14C dates on SPAC (N=3), pollen concentrate (N=2) and macro-charcoal (N=2); and the age model for ELZ01 is based on five AMS 14C dates on SPAC (N=5). The Bayesian age-depth models are presented in Figure 7.2.

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Table 7.1. 14C dates and calibrated ages for all samples from cores BSP02, FRN02 and ELZ01

Median Pre- 14C age Calibrated age (cal. yr 2 Lab. ID Fraction dated Calibrated age range depth (cm) treatment (BP)1 BP)2*+ BSP02 Wk-44690 SPAC 75 HyPy 3014±20 3060 - 3227 (99.6%) 3040 - 3227 3040 - 3043 (0.4%) Wk-44691 SPAC 149 HyPy 6430±23 7258 - 7420 (100%) 7258 - 7420 OZT912 Macro-charcoal 186.5 AAA 8890±60 9677 - 10189 (100%) 9677 - 10189 Wk-44692 SPAC 188.5 HyPy 8944±29 9900 - 10190 (100%) 9900 - 10190 9967 - 9983 (4.2%) OZU455 SPAC 233 HyPy 12100±40 13755 - 14085 (100%) 13755 - 14085 FRN02 OZU460 SPAC 48.5 HyPy 1215±25 1047 - 1119 (49.8%) 983 – 1177 1128 - 1177 (25.2%) 983 - 1030 (25%) OZT918 Macro-charcoal 50 AAA 1030±30 801 - 956 (100%) 801 - 956 OZU461 SPAC 95 HyPy 3505±25 3637 - 3835 (100%) 3637 - 3835 OZT163 Pollen 99.5 AAA 3395±40 3466 - 3697 (100%) 3466 - 3697 OZT162 Pollen 148 AAA 6960±40 7666 - 7848 (100%) 7666 - 7848 OZT917 Macro-charcoal 149.5 AAA 6980±210 7430 - 8182 (100%) 7430 - 8182 OZU462 SPAC 195.5 HyPy 10110±35 11392 - 11814 (99.1%) 11357 - 11814 11357 - 11373 (0.9%) ELZ01 OZU456 SPAC 35 HyPy 3175±25 3322 - 3407 (68.9%) 3251 - 3443 3251 - 3305 (26.3%) 3426 - 3443 (4.8%) OZU457 SPAC 56 HyPy 5355±35 5987 - 6211 (95.9%) 5946 - 6265 5946 - 5969 (2.5%) 6247 - 6265 (1.6%) OZU458 SPAC 76 HyPy 7790±35 8424 - 8599 (100%) 8424 - 8599 Wk-44693 SPAC 95.75 HyPy 8859±33 9686 - 9960 (79%) 9686 - 10151 10056 - 10151 (15.5%) 9987 - 10043 (5.5%) OZU459 SPAC 116.25 HyPy 12430±45 14129 - 14811 (100%) 14129 - 14811 11σ errors are given for 14C ages (reported at 68% probability) 22σ errors are given for calibrated ages (reported at 95.4% probability) *Calibrated against SHCal13 (Hogg et al., 2013) with OxCal V.4.2.4 (Bronk Ramsey, 2013) +Since calibration of 14C years to calendar years can result in a number of age ranges, the calibrated age ranges encompassing the largest proportion of total probability (%) are shown in bold and italicised font.

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The age-depth models indicate that each core covers the entire Holocene period, with BSP02 and ELZ01 extending into the late Pleistocene (BSP02 spans the last ~14,500 years, FRN02 spans the last ~12,050 years, and ELZ01 spans the last ~16,500 years). Whilst the age-depth model for ELZ01 suggests a basal age of ~16,500 cal. yr BP, it should be noted that the sedimentary composition of the core changes from an organic silty clay to sand below 119.5 cm (with a modelled age of ~14,800 cal. yr BP) (see Section 6.4.1; Field et al., 2018; Figure 7.5), below the lowest radiocarbon date at 116.25 cm (~14,100 cal. yr BP), with the sand layer likely to reflect fluvial deposition. Therefore the basal age of 16,500 cal. yr BP is based on projection of the model across a major sedimentary change. It is likely that there is a significant change in the sedimentation rate at 119.5 cm which is not accounted for in the age-depth model, i.e. that the sand unit has accumulated over a much shorter period of time and that the basal age for ELZ01 is closer to ~14,800 cal. yr BP (similar to BSP02), or is at least <16,500 cal. yr BP. Therefore, in the following text all dates below 119.5 cm will be referred to as ≥14,800 cal. yr BP).

Average growth rates were relatively consistent in BSP02 where they ranged from 0.12 - 0.23 mm/yr, slowing moderately between 13,870 and 10,040 cal. yr BP to 0.11 mm/yr. Growth rates in FRN02 and ELZ01 were more variable. In FRN02 they ranged from 0.19 – 0.12 mm/yr from the base of the core to 1070 cal. yr BP and increased to > 0.44 mm/yr in the uppermost sediments above 50 cm. In ELZ01 growth rates were comparatively slow, from 0.05 mm/yr from the base of the core to 10,050 cal. yr BP, before increasing to 0.14 mm/yr over the next ~1500 years and subsequently declining to 0.08 – 0.10 mm/yr from 8600 cal. yr BP to present. It should be noted that shifts in growth rates can in some cases be attributable to the discrete nature of radiocarbon sampling.

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7.4.2 Itrax µXRF elemental geochemistry

Selected key parameters and ratios (Ti, Fe, K, Si, Si/Ti, Mn/Ti, Ca, Cr Inc/Coh) for BSP02, FRN02 and ELZ01 are presented in Figure 7.3 -Figure 7.5. Since results are reported as centred log-ratios to minimise sample geometry effects (with the exception of Cr Inc/Coh), palaeoenvironmental conditions and/or information on spring dynamics can be derived from the relative changes in each of the elemental profiles. Loss-on-Ignition (% organic) is also plotted in Figure 7.3 -Figure 7.5, and demonstrates a close correspondence with Cr Inc/Coh ratios, which is similarly a measure of organic content within the cores (Section 7.5.1.1).

7.4.2.1 Correlation matrices

Correlation matrices for the key element counts and ratios are shown in Table 7.2. These matrices demonstrate that general patterns in lithogenic elements (Ti, K and Si) correlate strongly in BSP02 (r ≥ 0.86), however Si is more weakly correlated in FRN02, and only Ti and K correlate strongly in ELZ01 (r = 0.98). Si/Ti and Mn/Ti ratios are positively correlated at each of the three sites (r ≥ 0.78), and also with Ti (r ≥ 0.86). Strong negative correlations exist between Ca and lithogenic

152 Chapter 7 elements Ti and K, as well as for Si/Ti and Mn/Ti at the three springs. There is also a strong positive correlation between Cr Inc/Coh and Ca (r ≥ 0.80).

Ti Fe K Si Si/Ti Mn/Ti Ca BSP02 Fe 0.98 K 0.95 0.91 Si 0.86 0.83 0.91 Si/Ti 0.95 0.92 0.85 0.70 Mn/Ti 0.91 0.88 0.93 0.98 0.78 Ca -0.91 -0.92 -0.88 -0.93 -0.80 -0.94 Inc/Coh -0.84 -0.81 -0.88 -0.96 -0.67 -0.97 0.91 FRN02 Fe 0.89 K 0.93 0.74 Si 0.47 0.19 0.72 Si/Ti 0.91 0.76 0.82 0.35 Mn/Ti 0.86 0.67 0.84 0.50 0.97 Ca -0.94 -0.84 -0.88 -0.42 -0.89 -0.86 Inc/Coh -0.83 -0.63 -0.83 -0.52 -0.92 -0.95 0.80 ELZ01 Fe 0.51 K 0.98 0.44 Si 0.53 -0.09 0.61 Si/Ti 0.89 0.72 0.85 0.17 Mn/Ti 0.89 0.63 0.90 0.57 0.87 Ca -0.75 -0.59 -0.78 -0.64 -0.69 -0.93 Inc/Coh -0.87 -0.53 -0.89 -0.63 -0.78 -0.92 0.86

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7.4.2.2 Trends in element profiles

Geochemical records for each site are similar in terms of the overall trends displayed by the selected elements and ratios (see Figure 7.3 -Figure 7.5 and Figure 7.10), although the timing of some shifts differs between records. There is a close correspondence between elemental data and visible changes in sedimentary composition. For instance, a large proportion of the older part of each record is dominated by clastic sediments. Therefore the abundance of lithogenic elements (Ti, Fe, Si and K) is greatest in these units. At each site the basal sediments are characterised by higher concentrations of Ti which decline in the mid-Holocene at or after ~7000 cal. yr BP (~7200 cal. yr BP in BSP02 and ELZ01 and later in FRN02 at ~6200 cal. yr BP) although this trend is far less pronounced in ELZ01. The importance of lithogenic elements becomes increasingly variable up- core, although there is a pronounced peak in abundance centred at ~ 4800 - ~3400 cal. yr BP, most notably in BSP02 and FRN02.

Ratios of Si/Ti and Mn/Ti are greatest in the basal sections of the springs, before declining up-core. This decline occurs first in FRN02 at ~10,200 cal. yr BP with a subsequent decline at ~6200 cal. yr BP, and much later in BSP02 (~7900 cal. yr BP) and ELZ01 (~7400 cal. yr BP). Both the Si/Ti and Mn/Ti ratios become more variable up-core, with peaks corresponding to increases in lithogenic elements around the mid-late-Holocene. Most notably, a peak in both ratios occurs between ~ 4800 - ~3400 cal. yr BP. Of note, the peak in Si/Ti and Mn/Ti ratios is immediately preceded by a pronounced reduction in both ratios occurring from ~6200 cal. yr BP in FRN02 and later in ELZ01 (~5300 cal. yr BP) and BSP02 (4800 cal. yr BP).

Counts of Ca and the Cr Inc/Coh ratio are lowest in the basal sediments at each site, generally increasing up-core. In BSP02 both parameters initially increase at ~10,800 cal. yr BP and then again from ~9200 cal. yr BP. The timing of the first increase in FRN02 is similar (~10,500 cal. yr BP) although the second increase is much later (~6200 cal. yr BP). Trends in ELZ01 are more subtle with increasing values observed from ~9400 cal. yr BP. Lower Ca and Cr Inc/Coh ratios correspond with increasing values in lithogenic elements and Si/Ti and Mn/Ti ratios around the mid-late-Holocene.

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7.4.3 Pollen, NPPs and micro-charcoal

The local pollen sum and micro-charcoal records from BSP02 (Figure 7.7), FRN02 (Figure 7.8) and ELZ01 (Figure 7.9) differ in terms of species composition and overall trends (see Figure 7.10). For instance, in BSP02 there is a general overall trend of declining wetland taxa and increasing spring taxa up-core, whereas the opposite occurs in ELZ01 (Figure 7.6). The FRN02 record is more variable. Species composition is also different in each record, with vine thicket taxa such as T. timon abundant in the BSP02 record, while monolete fern spores comprise a much larger part of the FRN02 record than at the other sites. Wetland taxa are also less diverse at BSP02 with C. dubium and Cyperaceae being of importance whilst Myriophyllum and Typha comprise a large portion of the wetland taxa in FRN02 and ELZ01.

Despite the differences in the current vegetation assemblage growing on the three studied springs (see Section 2.5) and in the spring-taxa pollen records, the vegetation surrounding each of the three sites (regional pollen sum) is relatively similar to each other (predominantly comprised of Poaceae and Eucalyptus). There is little overall change in Poaceae or Eucalyptus throughout the records, with the exception of Gap Springs where the representation of Poaceae increases at the expense of Eucalyptus from ~ 8900 cal. yr BP and particularly in the late-Holocene from ~1650 cal. yr BP, and at Fern Pool where there is a marked decline in Eucalyptus centred at ~2200 cal. yr BP (Figure 7.6). NPP records from the three sites are strongly correlated, with increasing accumulation rates of all NPPs within the late-Holocene (see Figure 7.7 - Figure 7.9 and Figure 7.10). Table 7.3 lists the NPPs encountered in this study and their indicative values. Pollen, NPP and micro-charcoal results for each record are discussed in more detail below.

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Table 7.3. Indicative values of the NPPs encountered in this study (adapted from Carrión and

Navarro, 2002)

NPP Indication Reference

Entorrhiza Root activity from Cyperaceae and Riess et al. (2015) Juncaeceae

Glomus Catchment erosion, root activity Van Geel et al. (1989), Carrión et al. (1995, 1999), Cook et al. (2011)

Pseudoschizaea Drought, desiccation, seasonal drying, Scott (1992) relatively warm climate

Tilletia Fungal activity Van Geel (1972), Navarro et al. (2000), Shumilovskikh et al. (2015)

7.4.3.1 Black Springs (BSP02) (Figure 7.7)

CONISS assisted in the location of six pollen zones, as follows:

BPS02_01: 244 – 235 cm (14,520 – 14,040 cal. yr BP)

The basal zone is dominated entirely by wetland pollen with the perennial aquatic C. dubium comprising 100% of the local pollen sum. There is limited species richness in the surrounding landscape, with Poaceae comprising 82 % and Eucalyptus the remaining 18 %. Pollen and charcoal accumulation rates are very low, and no NPPs were recorded within this zone.

BSP02_02: 235 – 175 cm (14,040 – 9120 cal. yr BP)

Spring taxa abruptly increase in this zone. In particular, Melaleuca increases from 210 cm (11,870 cal. yr BP), whilst wetland taxa are common and comprised of Cyperaceae and C. dubium. The composition of the surrounding landscape remains relatively unchanged from the preceding zone, although additional taxa such as Asteraceae and Dodonaea are present in low percentages. Pollen accumulation rates steadily increase up-zone, whilst there is a small peak in charcoal accumulation rates at 190 cm (10,130 cal. yr BP). NPPs are either rare or absent.

BSP02_03: 175 – 155 cm (9120 – 7730 cal. yr BP)

In this zone C. dubium increases in abundance to the point where it comprises ~75% of the local pollen sum, whilst Cyperaceae and Melaleuca decline. Pandanus shows a small increase towards the top of the zone. In the surrounding landscape there is a slight increase in abundance of Poaceae at the expense of Eucalyptus, the latter now comprising ~20% of the regional pollen sum. Pollen

160 Chapter 7 accumulation rates are relatively steady, whilst charcoal accumulation rates are very low. NPPs remain rare or absent.

BSP02_04: 155 – 95 cm (7730 – 4280 cal. yr BP)

There is a dramatic increase in spring taxa at the expense of wetland taxa from the base of this zone. In particular there is an increase in Pandanus which comprises, on average, 53% of the spring pollen sum in this zone, and a decrease in C. dubium. T. timon, predominantly absent in preceding zones, is present. In the surrounding landscape taxa such as Asteraceae, Dodonaea, Wrightia and Amaranthaceae are more abundant. Charcoal accumulation rates increase, with a peak at 110 cm (5130 cal. yr BP).

BSP02_05: 95 – 15 cm (4280 – 580 cal. yr BP)

T. timon is more abundant in this zone and is recorded by two peaks centred at 85 cm (3700 cal. yr BP) and 40 cm (1670 cal. yr BP). Monolete fern spores are more abundant than in preceding (older) zones, comprising ~6% of the spring pollen sum. There are also dramatic increases in all NPP accumulation rates towards the top of the zone from ~70 cm (2950 cal. yr BP), with all but Glomus reaching peak concentrations at 40 cm (1670 cal. yr BP). Charcoal accumulation rates also feature a sharp peak at 30 cm (1230 cal. yr BP).

BSP02_06: 15 – 0 cm (580 cal. yr BP – present)

The uppermost zone is characterised by a dominance of spring taxa, in particular T. timon (~53% of the local pollen sum), whilst monolete fern spores and wetland taxa are less common. The composition of the surrounding landscape taxa remains relatively unchanged from the preceding zone, however all NPPs (with the exception of Glomus) decrease dramatically. Pollen and charcoal accumulation rates also decrease towards the top of the core.

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7.4.3.2 Fern Pool (FRN02) (Figure 7.8)

CONISS assisted in the location of five pollen zones, as follows:

FRN02_01: 204 – 195 cm (12,050 – 11,570 cal. yr BP)

In the basal zone monolete fern spores and Pandanus are abundant, comprising 28% and 39% of the local pollen sum respectively. Wetland taxa are also present, predominantly C. dubium and Cyperaceae, whilst in the surrounding landscape species richness is low with Eucalyptus and Poaceae comprising 55% and 39% of the regional pollen sum respectively. Accumulation rates for pollen and charcoal are very low, whilst NPPs are either rare or entirely absent.

FRN02_02: 195 – 175 cm (11,570 – 9940 cal. yr BP)

This zone is characterised by an increase in much higher percentages of Typha which dominates the aquatic assemblage. Of the spring taxa, Pandanus is less abundant than within the preceding zone whilst Melaleuca increases as part of a longer term trend. There is little change in the abundance of monolete fern spores or vegetation in the surrounding landscape, however pollen and charcoal accumulation rates are slightly higher and Pseudoschizaea is represented.

FRN02_03: 175 – 95 cm (9940 – 3700 cal. yr BP)

Unlike the preceding zone, Typha is largely absent whilst Myriophyllum and Cyperaceae increase in abundance. Melaleuca is higher than in preceding zones, comprising on average 42% of the local pollen sum and up to 84% at the top of the zone (100 cm; 3780 cal. yr BP). Values for Eucalyptus and Poaceae generally fluctuate throughout, with a peak in Eucalyptus and dip in Poaceae also at 100 cm (3780 cal. yr BP). Accumulation rates of pollen, charcoal, Pseudoschizaea and Tilletia all increase towards the top of the zone from ~120 cm (5440 cal. yr BP).

FRN02_04: 95 – 35 cm (3700 – 740 cal. yr BP)

There is a pronounced decline in Melaleuca in the middle of this zone centred at 70 cm (2220 cal. yr BP). This corresponds with a decline in Eucalyptus and increase in Poaceae in the surrounding landscape, whilst there is also a matching peak in Pseudoschizaea accumulation rates at this time. Tilletia is rare, however Glomus and Entorrhiza increase in the uppermost sample (40 cm; 850 cal. yr BP). Meanwhile, pollen and charcoal accumulation rates are generally higher than in previous zones.

FRN02_05: 35 – 0 cm (740 cal. yr BP – present)

Monolete fern spores generally display a decreasing trend up-core whilst the abundance of spring taxa O. basilicum/B. polystachyon increases. NPP accumulation rates increase up core, with the 163 Chapter 7 exception of Pseudoschizaea. Charcoal accumulation rates are high throughout, whilst pollen accumulation rates increase sharply in the uppermost sample.

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7.4.3.3 Gap Springs (ELZ01) (Figure 7.9)

CONISS assisted in the location of five pollen zones, as follows:

ELZ01_01: 135.5 – 124 cm (≥14,800 cal. yr BP)

Pandanus is abundant in this zone, comprising 40% of the local pollen sum, whilst the wetland taxa are dominated by Myriophyllum (30%). Monolete fern spores are only of notable value for the core in this sample. In the surrounding landscape species richness is low (Poaceae and Eucalyptus), dominated by Poaceae (71%) of the regional pollen sum. NPPs are absent, whilst charcoal and pollen accumulation rates are extremely low.

ELZ01_02: 124 – 79 cm (≥14,800 – 8910 cal. yr BP)

The aquatic assemblage in this zone is marked by a dramatic decrease in Myriophyllum (on average comprising just 5% of the local pollen sum), and the presence of which was absent in the preceding zone. Pandanus is fairly abundant, whilst there is an increase in Melaleuca, comprising on average 54% of the local pollen sum. Monolete fern spores are predominantly absent. Values of Eucayptus (Poaceae) increase (decrease) until 116.5 cm (14,160 cal. yr BP), before a decline (increase) centred at 101.5 cm (10,750 cal. yr BP), followed by subsequent recovery (decline). NPP’s are absent, although pollen accumulation rates increase to peak values at 97 cm (10,160 cal. yr BP). There is a sharp peak in charcoal accumulation rates in the lowermost sample (~15,080 cal. yr BP) followed by considerably lower values for the remainder of this zone.

ELZ01_03: 79 – 32.5 cm (8910 – 3130 cal. yr BP)

This zone is characterised by a slight decline in Pandanus and increase in Myriophyllum. At the base of the zone (76.5 cm; 8,640 cal. yr BP), there are record peaks in Melaleuca and Eucalyptus. Decreasing Eucalyptus pollen through this zone implies a decrease in the abundance of this genus relative to grasses in the landscape. Of the NPPs, Pseudoschizaea is sporadically present, whilst Glomus is present in small amounts. In general pollen and charcoal accumulation rates fluctuate, with a noted decline in abundance centred at 45.5 cm (4720 cal. yr BP).

ELZ01_04: 32.5 – 17.5 cm (3120 – 1650 cal. yr BP)

This zone is marked by a decrease in the representation of spring taxa, and an increase in wetland taxa, in particular Myriophyllum. Pollen representative of vegetation surrounding Gap Springs in dominated by Poaceae (~80%). Of note is a dramatic increase in Pseudoschizaea between 25 – 20 cm (2390 – 1910 cal. yr BP). Pollen and charcoal accumulation rates are low by comparison to the preceding two zones.

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ELZ01_05: 17.5 – 0 cm (1650 cal. yr BP – present)

In this uppermost zone wetland taxa, in particular Myriophyllum, dominate the local pollen sum while Poaceae pollen comprises ~88% of the regional pollen sum. With the exception of Pseudoschizaea, all NPPs peak at 5 cm (440 cal. yr BP) which corresponds with a peak in pollen accumulation rates.

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Figure 7.9. Summary pollen diagram of ELZ01 (pteridophytes, wetland and spring taxa included within the local pollen sum; grass and tropical savanna taxa included within the regional pollen sum), with generalised stratigraphy, key pollen taxa (>5 % in at least one sample) and accumulation rates for pollen, charcoal and NPPs plotted. Also shown are the results of CONISS analysis which guided the identification of the five pollen zones shown (labelled ELZ01_01 – ELZ01_05) 168 Chapter 7

7.4.4 Statistical analysis

7.4.4.1 Principal Components Analysis (PCA)

The PCA results for the three datasets (Itrax µXRF, pollen, and NPPs) plotted with age uncertainty, provide a visual indication of change in the records, and the degree of similarity between the different datasets from each site (Figure 7.10). Species scores for the variables selected for PCA for each dataset at each site are shown in Table 7.4. The PCA axis 1 scores and species scores for both the Itrax µXRF and NPP datasets demonstrate that broadly similar patterns of change occur at each site (Figure 7.10; Table 7.4). The Itrax µXRF PCAs for each spring show a general pattern of low (high) values until ~11,000 cal. yr BP at Black Springs and Gap Springs, and until ~6000 cal. yr BP at Fern Pool, before increasing (decreasing) until present day (Figure 7.10). In addition, there is a reversal to lower (higher) values centred at ~4000 cal. yr BP. The NPP PCAs for each spring exhibit a pattern of increasing values after ~4,000 years, increasing more substantially within the last 1000 – 2000 years. The NPP PCAs then decrease after ~500 cal. yr BP (most noticeably at Black Springs and Gap Springs) (Figure 7.10). There is no coherency between each site in the pollen PCA axis 1 scores or species scores (Figure 7.10; Table 7.4).

Figure 7.10. Time series of PCA axis 1 scores for Itrax µXRF, pollen, and NPP data at each site. The black lines depict the data on their age models as presented in Figure 7.3 - Figure

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7.9. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 10,000 iterations of age-depth modelling

Table 7.4. Species scores for variables selected for PCA for each dataset at each of the three sites (Itrax µXRF, pollen, and NPPs)

BSP02 FRN02 ELZ01

Axis 1 Axis 2 Axis 1 Axis 2 Axis 1 Axis 2

Itrax µXRF Al 0.93 -0.24 -0.89 0.00 -0.88 -0.31 Ar -0.86 -0.19 0.86 -0.06 0.68 -0.48 Ca -0.91 -0.22 0.91 -0.23 0.98 -0.02 Cs -0.38 -0.42 0.77 -0.14 Cu -0.31 0.93 0.40 0.78 0.87 -0.24 Fe 0.97 0.12 -0.92 0.04 -0.60 0.71 K 0.98 -0.04 -0.95 -0.06 -0.96 -0.17 Mn -0.97 -0.15 0.98 0.04 0.98 -0.02 Nd 0.87 -0.12 0.24 -0.02 Ni -0.95 -0.16 P -0.40 0.67 0.62 -0.15 Pm -0.97 -0.16 0.98 0.02 0.97 -0.04 Rb -0.33 0.60 0.10 -0.01 S -0.87 0.35 Se -0.92 0.05 Si 0.95 -0.26 -0.60 -0.24 -0.52 -0.78 Ta -0.88 -0.18 Ti 0.98 0.09 -0.98 -0.08 -0.97 -0.03 Zr 0.86 0.08 -0.90 0.05 -0.85 -0.14 Pollen Acacia 0.48 0.05 -0.25 0.24 Adriana glabrata var. acerifolia -0.15 -0.28 -0.03 -0.22 Aidia racemosa 0.67 0.65 AMARANTHACEAE -0.37 0.49 0.03 0.01 0.05 -0.57 Amyema -0.03 -0.01 -0.11 0.02 ASTERACEAE -0.07 0.44 0.19 0.29 0.29 -0.40 Atalaya hemiglauca -0.38 0.76 Banksia dentata -0.06 0.18 -0.09 0.08 0.05 -0.57 BRASSICACEAE 0.44 0.09 -0.08 0.00 0.74 0.37 Breynia cernua 0.09 0.15 0.38 -0.50 0.40 -0.04 Buchanania obovata -0.02 -0.57 Callitris -0.38 0.76 0.71 0.40 0.86 -0.15 Casuarina 0.26 0.53 -0.06 -0.03 Celtis philippinensis 0.67 0.65 Clerodendrum floribundum 0.00 0.00 Codonocarpus cotinifolius 0.42 0.17 0.33 0.50 0.61 -0.12

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Colocasia esculenta 0.02 0.01 -0.28 0.18 0.16 -0.64 Cycnogeton dubium 0.69 0.21 0.67 -0.30 0.56 -0.48 CYPERACEAE 0.63 0.36 0.69 -0.37 0.75 0.55 Decaisnina signata 0.44 0.09 Dodonaea 0.01 0.27 0.65 0.30 0.44 0.27 Drosera 0.13 -0.36 Elaeocarpus 0.00 0.12 Eremophila 0.34 0.51 ERICACEAE 0.03 0.01 Eucalyptus 0.69 0.25 -0.15 -0.16 -0.05 0.67 Euphorbia 0.04 0.77 0.75 0.03 0.17 0.46 EUPHORBIACEAE -0.12 -0.08 -0.10 -0.19 Fabaceae 0.76 0.25 -0.31 0.23 Ficus 0.04 -0.02 Gomphrena 0.71 0.32 -0.30 0.02 0.89 -0.12 Grevillea -0.38 0.76 0.16 -0.27 0.23 0.50 Hypericum gramineum 0.04 -0.02 Mallotus 0.02 -0.04 0.13 -0.15 Melaleuca 0.26 0.56 0.30 -0.45 0.15 0.77 Melastoma affine -0.25 0.74 0.74 0.55 0.68 0.00 Monolete fern spore -0.48 0.58 0.73 0.10 0.64 -0.30 Myriophyllum -0.16 -0.03 0.29 -0.47 0.87 -0.35 MYRTACEAE -0.32 0.26 Ocimum basilicum/Basilicum polystachyon -0.37 0.36 0.38 -0.46 0.18 0.09 Opilia amentacea -0.30 0.02 -0.30 0.17 Pandanus -0.45 0.24 0.54 -0.55 -0.27 0.38 Picea -0.17 -0.09 -0.19 0.16 Plantago -0.15 -0.28 0.49 -0.61 0.37 0.66 Plectranthus congestus -0.16 0.10 0.20 -0.40 0.27 -0.07 POACEAE 0.64 0.28 0.57 -0.32 0.88 0.37 Pouteria sericea 0.58 0.32 PROTEACEAE 0.11 -0.14 -0.10 0.19 SAPINDACEAE -0.40 0.31 0.25 0.69 SAPOTACEAE 0.04 0.02 Timonius timon -0.56 0.28 0.18 0.31 Trilete fern spore 0.36 0.26 -0.02 0.42 0.91 -0.05 Typha 0.43 0.12 -0.06 0.00 -0.25 -0.07 Ventilago viminalis 0.34 0.17 VERBENACEAE -0.04 -0.11 Vigna lanceolata 0.45 0.24 -0.18 -0.14 -0.11 -0.04 Wrightia -0.38 0.37 0.35 -0.46 0.78 -0.14 NPPs Entorrhiza 0.90 -0.34 0.80 -0.06 0.97 0.09 Glomus 0.84 0.53 0.92 -0.27 0.99 -0.01 Pseudoschizaea 0.96 -0.07 0.34 0.94 -0.08 1.00 Tilletia 0.94 -0.07 0.72 -0.03 0.99 0.00

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7.4.4.2 Monte Carlo empirical orthogonal functions (MCEOF)

Both leading MCEOF (regional EOF1) plots of the Si/Ti (Figure 7.11) and Pseudoschizaea data (Figure 7.12) from the three springs indicate these parameters respond primarily to a common regional forcing – namely climate variability – during the late Quaternary. They also correspond relatively well with the local PCA axis 1 scores from which they are based, in particular the Pseudoschizaea MCEOF results (see Figure 7.10 - Figure 7.12). All three sites load positively on EOF1 for both proxies, where Si/Ti explains 89.6 ± 2.6% (2σ) and Pseudoschizaea explains 81.3 ± 11.4% % (2σ) of the variance, assessed using the broken stick approach (Figure 7.13).

Si/Ti regional EOF1 scores (Figure 7.11) display a trend of slowly increasing Si/Ti from 14,500 cal. yr BP, intensifying from ~12,000 cal. yr BP. After this time, Si/Ti regional EOF1 levels peak at ~11,000 cal. yr BP and plateau until ~7500 cal. yr BP. They then decline through to present day with the exception of two regions of higher values centred at ~6400 cal. yr BP and a more abrupt change at ~4200 cal. yr BP.

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Figure 7.11. MCEOF Si/Ti synthesis for BSP02, FRN02 and ELZ01. Time series of local Si/Ti records at each site presented in blue, with the black lines depicting data on their age models as presented in Figure 7.3 - Figure 7.5. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Y axes are oriented to show higher Si/Ti ratios plotting upwards. The results of the MCEOF proxy Si/Ti synthesis are presented in red, with the black line depicting the median, dark red shading = 90% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 10,000 iterations of age-depth modelling

Pseudoschizaea regional EOF1 scores (Figure 7.12) indicate absent/low values of Pseudoschizaea until ~5500 cal. yr BP, after which there is a slight increase in accumulation rates followed by a subsequent minor decrease at ~5000 cal. yr BP. A dramatic increase in Pseudoschizaea then occurs from ~2600 cal. yr BP reaching peak values by 2000 cal. yr BP. Pseudoschizaea values remain high for ~1000 years before decreasing during the last millennium.

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Figure 7.12. MCEOF Pseudoschizaea synthesis for BSP02, FRN02 and ELZ01. Time series of local Pseudoschizaea records at each site presented in blue, with the black lines depicting data on their age models as presented in Figure 7.7 - Figure 7.9. Dark blue shading = 95% confidence intervals, pale blue shading = 68% confidence intervals. Y axes are oriented to show higher Pseudoschizaea accumulation rates plotting upwards. The results of the MCEOF proxy Pseudoschizaea synthesis are presented in red, with the black line depicting the median, dark red shading = 90% confidence intervals, pale blue shading = 68% confidence intervals. Confidence intervals are derived from 2000 iterations of age-depth modelling

7.5 Discussion

7.5.1 Interpretation of Itrax µXRF data

A number of palaeoenvironmental interpretations can be drawn from variability in the elemental profiles and ratios which are discussed in this section.

An increase in Ca counts occurred toward the top of all three of the springs (Figure 7.3 -Figure 7.5). Calcium may be derived either allochthonously as a result of carbonate weathering in the

174 Chapter 7 catchment, from in-situ biogenic calcium carbonate precipitation, or from authigenic calcium carbonate precipitation (e.g. calcite precipitation) from evaporative concentration (Davies et al., 2015). On the Kimberley Plateau, which is predominantly a sandstone landscape (Figure 7.1), there is no significant secondary calcium carbonate (Green et al., 2017). Consequently there is limited potential for allochthonous transport of carbonate minerals to the springs. SEM analysis also implied no presence of biogenic calcium carbonate in the sediments. It therefore seems most likely that elevated Ca in these archives is derived from autochthonous calcium carbonate precipitation from groundwater, i.e. evaporative concentration (e.g. Scholz et al., 2007; Brown 2011).

In contrast to Ca, lithogenic elements such as Ti, Fe and K are commonly associated with lithic flux (although Fe in particular is often derived from post depositional modification due to changes in redox conditions and diagenesis (Engstrom and Wright, 1984; Mackereth, 1996; Boyle, 2001)). Due to their origin, relative stability and conservative behaviour (Boës et al., 2011), the accumulation of these sediments in the springs is assumed to be largely allochthonous (although K is relatively water soluble (Clift et al., 2014)), associated with alluvial deposition of sediment derived from erosion of Kimberley Plateau lithologies.

Minerogenic Si typically behaves conservatively in most environments, however, in biologically productive environments the autochthonous production or transport of biogenic Si can contribute to Si concentration (Brown, 2015). This is the case in the studied springs, where SEM analysis confirmed the presence of significant volumes of biogenic Si (predominantly phytoliths). Phytoliths are thought to be derived primarily from in-situ deposition however they can also be transported into a site via fluvial and aeolian processes (Piperno, 2006) under wetter or drier conditions respectively. By comparison, Ti is generally regarded an unambiguous indicator of allochthonous input in alluvial environments (Cohen, 2003). For that reason, variability in its concentration has commonly been used as a proxy for increased rainfall/runoff and wetter conditions (see Davies et al., 2015 and references within) or as an indicator of aeolian input (Yancheva et al., 2007; Bakke et al., 2009). In the context of the studied springs which have the potential to record both alluvial and aeolian sedimentation, Ti counts, at face value, may represent contributions of either. Accordingly, it is essential to establish covariance with other elements to assess transport mechanisms of Ti (Davies et al., 2015). Regardless of its origin, Ti is generally relatively stable post-deposition (Montero-Serrano et al., 2010) and as a result can be used as a tool for normalisation to show authigenic processes, i.e. biological production. Consequently, Si/Ti ratios are commonly used as a proxy for authigenic (biogenic) silica, derived principally from phytoliths, diatoms, cryosphytes, and sponge spicules (Davies et al., 2015). Increases in Si/Ti ratios are then interpreted as reflecting

175 Chapter 7 greater biogenic silica productivity (e.g. Brown et al., 2007; Stansell et al., 2010; Balascio et al., 2011; Brown, 2011; Burnett et al., 2011; Kylander et al., 2011; Martin-Puertas et al., 2012; Melles et al., 2012). Due to the relationship between biological production and moisture availability, increased biogenic silica and/or diatom abundance has been found to correlate with elevated site moisture (e.g. Poulíčková et al., 2004; Rühland et al., 2006; Fukomoto et al., 2012; Hargan et al., 2015).

Mn/Ti ratios, by comparison, can be used as a proxy for changes in redox conditions (e.g. Kylander et al., 2011; Moreno et al., 2011) due to ventilation of the water column during water level fluctuations, or a reduction in respiration as a result of greater influx of organic matter (Davison, 1993), as Mn forms an insoluble oxide in conditions where oxygen is abundant (Kylander et al., 2011). Finally, the incoherence/coherence (Cr Inc/Coh) scattering ratio is commonly used as a proxy for changes in organic content, since organic carbon has a lower average atomic mass and is therefore not resolved by the Itrax core scanner (Jenkins, 1999; Guyard et al., 2007; Burnett et al., 2011). The LOI (% organic) closely mirrors Cr Inc/Coh (Figure 7.3 -Figure 7.5), confirming that Cr Inc/Coh is a reliable proxy for organic matter in these sites.

7.5.1.1 Elemental geochemistry as a proxy for monsoon activity

Minerogenic accumulation in the springs, as reflected by the µXRF data, provides a valuable means to trace spring development and associated regional climate and hydrology. Interpreting regional climate and hydrology is possible since moisture availability at these springs is dependent on monsoonal precipitation feeding recharge (see Section 7.2).

Increases in Ca towards the top of the cores indicate increased evaporative concentration of calcium carbonate. On one hand, increased Ca could be interpreted as indicating increased drying in the cores implying a reduction in regional spring discharge in the mid- to late-Holocene, i.e. a reduction in monsoonal precipitation. On the other hand, increased Ca precipitation could reflect internal dynamics. For instance, as the sedimentary mass at each spring site accumulated through time, the height of the mound increased relative to the spring pressure. This makes it increasingly likely that upper sections of the spring experienced drying toward the end of the dry season, leading to increased precipitation of Ca. This may occur independent of any regional precipitation changes. A further possibility is that both processes contribute to increased Ca precipitation.

A strong negative correlation exists between Ca and Ti at all springs (r ≥ 0.75). Because Ti counts reflect the delivery of allochthonous sediment to the springs, the decrease in Ti recorded at the top of the cores implies a decrease in sediment delivery, most likely due to a reduction in alluvial

176 Chapter 7 sedimentation. This can be interpreted as implying drier conditions in the uppermost sediments. Alternatively, the decrease in Ti may reflect spring development which may limit the ability for detrital Ti to be transported into the springs. For example, prior to the development of a mound detrital sediment may be derived from catchment runoff and upwelling groundwater. These sources are likely to swamp aeolian sedimentation. However, as the spring develops the contribution from runoff will decline (see Section 5.1.1 and Field et al., 2017 for a summary of spring development) reducing Ti delivery.

There is a strong positive correlation between Si/Ti ratios and Ti at the springs (r ≥ 0.89), e.g. despite the reduction in Ti counts at the top of the cores there is a coeval reduction in the Si/Ti ratio. Assuming the Si/Ti ratio remains consistent in the allochthonous sediment supplied to the springs, this implies a decrease in biogenic silica in the upper sediments. This is likely in response to reduced moisture availability limiting phytolith production. Consequently, the Si/Ti ratio in these springs likely reflects changes in spring moisture, and can be used as a qualitative proxy for monsoonal aquifer recharge and by association, monsoon precipitation. Si/Ti regional EOF1 scores are therefore assumed to reflect regional trends in monsoon activity. It is worth noting, however, that some of the Si/Ti patterns may be influenced by variability in the Si/Ti ratio of mineral matter transported to the springs, although the Si/Ti ratio does not match the dust record developed by McGowan et al. (2012) for Black Springs implying that aeolian dust input is not a controlling factor.

Si/Ti ratios at the studied springs are inversely related to organic content, e.g. with negative correlations between Si/Ti and Inc/Coh ratios (r ≥ 0.67 respectively) and LOI values. At face value, this seems counterintuitive given that in these records organic contents are highest when biogenic silica (i.e. phytolith) productivity is lower (e.g. in the upper sediments). However, the positive correlations between Mn/Ti and Si/Ti ratios (r ≥ 0.78), and negative correlations between Mn/Ti and Inc/Coh ratios (r ≥ 0.92) could imply that the presence of highly oxygenated groundwater limited the preservation of organic matter at times of greater biogenic silica productivity, e.g. in the lower spring sediments. Increasing organic matter up-core at the studied springs is therefore not necessarily attributable to increased organic productivity, rather it may reflect changing preservation conditions made possible as dissolved oxygen in groundwater is used in reduction reactions and/or biological activity higher in spring mounds.

7.5.2 IASM variability over the last 14,500 years

Evidence for changes in IASM variability from the three spring records is presented below, with a conceptual representation of these presented in Figure 7.14. 177 Chapter 7

7.5.2.1 Regional-scale evidence: robust trends reliably shared across the three springs

The records from Black Springs and Gap Springs indicate that precipitation in the Kimberley increased from as early as ~≥14,500 cal. yr BP. This is shown by the accumulation of sediment at both Black Springs (from ~14,520 cal. yr BP) and Gap Springs (from ~≥14,820 cal. yr BP) from at least this time. Since the groundwater flowing from these springs is derived from small aquifers recharged locally and immediately by precipitation, this onset of sedimentation likely coincides with an increase in monsoonal precipitation which would have elevated or instigated spring discharge at these sites. The slow increase in the Si/Ti regional MCEOF1 scores from 14,500 - 12,000 cal. yr BP (Figure 7.11) also suggests a moderate and sustained increase in precipitation during the late Pleistocene, resulting in increasing biogenic Si productivity, whilst the basal sediments at each of the three springs are characterised by higher concentrations of lithogenic elements, in particular Ti, suggestive of increased rainfall and runoff. The timing of this initial increase in monsoon activity from ~14,500 cal. yr BP corresponds with flooding of the Sunda shelf in response to Meltwater Pulse 1A between ~14,600 – 14,300 yrs BP (Hanebuth et al., 2000). This is hypothesised to have intensified tropical convection and moisture advection over the IASM region during the Austral summer (DiNezio and Tierney, 2013). The results of palaeoclimate modelling also indicate that an active Australian monsoon (albeit weaker than previous “active” monsoon periods) would be expected during the late Pleistocene (Wyrwoll et al., 2007).

There is a more rapid increase in Si/Ti MCEOF1 scores from 12,000 cal. yr BP coincident with the onset of sedimentation at Fern Pool. This onset coincides with maximum spring discharge at Black Springs and Gap Springs, as implied by Si/Ti ratios. Whilst these records indicate an intensification in monsoon activity at ~12,000 cal. yr BP, no clear expression of millennial-scale pulses of rainfall variability associated with the B/A or H0 is apparent. However, both of these events were identified in speleothems in the Kimberley’s east (Denniston et al., 2013a). Although the role of H0 on Australian climate is debated (Tibby, 2012), it is possible that the increase in monsoon activity at ~12,000 cal. yr BP is, in part, due to the southward “push” of the ITCZ driven by Northern Hemisphere cooling during H0 (Broccoli et al., 2006; Muller et al., 2008; Denton et al., 2010; Mohtadi et al., 2011). The increase in moisture from ~12,000 cal. yr BP at the springs also broadly coincides with increased temperatures following the Antarctic Cold Reversal, and it has been proposed that the southward displacement of the ITCZ during H0 was accentuated in the Southern Hemisphere by the increase in greenhouse gas warming (Kuhnt et al., 2015).

The general view of this period across northern Australia is that the IASM strengthened at ~14,000 yrs BP (Reeves et al., 2013). Other sites within the Kimberley and offshore indicate similar timings

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(e.g. van der Kaars, 1991; Wyrwoll and Miller, 2001; van der Kaars and De Deckker, 2002; Kawamurra et al., 2006; Kershaw et al., 2006; van der Kaars et al., 2006; Denniston et al., 2013a; Kuhnt et al., 2015; Vannieuwenhuyse et al., 2017), including a strengthened monsoon from 12,000 cal. yr BP (Wende et al., 1997; Kuhnt et al., 2015), also implied by the studied springs. However, it is interesting to note that some records from northeast Australia imply relatively dry conditions at this time (Moss et al., 2017). Prior to 14,000 yrs BP in the Kimberley there is evidence for a less active monsoon and enhanced aridity during the LGM and late Pleistocene. This resulted in the abandonment of archaeological sites (see Section 4.5.1; O’Connor and Veth, 2006) and increased aeolian activity (Wende et al., 1997; Fitzsimmons et al., 2012). Additionally, rock paintings in the Kimberley considered to be from this period (Ouzman et al., 2017; Veth et al., 2017a) show hunting scenes featuring abundant macropods (Walsh, 2006) and the Greater Bilby (Macrotis lagotis) (Walsh, 2000), all suggestive of drier and more open tropical savannah environments (see Section 4.5.1).

The high Si/Ti regional MCEOF1 scores between ~11,000 - 7500 cal. yr BP (Figure 7.11) indicate a sustained period of elevated monsoonal precipitation beginning in the early-Holocene and persisting until the mid-Holocene. At the same time lithogenic elements remain abundant (e.g. Ti, K, Si as well as Fe), indicative of the continued supply of alluvial sediment to the springs. The timing of this region of high Si/Ti in the springs coincides with a rapid increase in precipitation elsewhere in the IASM region (e.g. Partin et al., 2007; Griffiths et al., 2009).

The increase in monsoonal precipitation between ~11,000 – 7500 cal. yr BP coincides with the flooding of the Sunda shelf (Griffiths et al., 2009), facilitating increased moisture advection and tropical convection over the Kimberley. The effects of this sea level rise were potentially accentuated by warmer waters in parts of the IPWP region as a result of Northern Hemisphere insolation-induced heating (Griffiths et al., 2009). Furthermore, modelling studies have indicated that even during periods of insolation minima in the low latitudes of the Southern Hemisphere (e.g. at the Pleistocene-Holocene boundary and into the early-Holocene in northwest Australia) high orbital tilt values were important in producing strong monsoon flow when coupled with these warmer SSTs (Liu et al., 2003; Wyrwoll et al., 2007). This increase in precipitation during the early-Holocene is also expressed in other records across the Kimberley (Jennings, 1975; Thom et al., 1975; McConnell and O’Connor, 1997; Denniston et al., 2013a, 2013b; Proske et al., 2014; Haberle, 2015) and offshore (van der Kaars et al., 2006; Kuhnt et al., 2015). Similarly, previous work at Black Springs demonstrated an increase in peat humification from the early-Holocene at ~9600 cal. yr BP with a further intensification between 8500 – 7000 cal. yr BP, interpreted as

179 Chapter 7 implying increased moisture (Field et al., 2017). Extreme flood event(s) have also been implied in the Kimberley during this period, as evidenced by cosmogenic nuclide exposure ages on fluvial boulders in the Durack River which date from 10,300 ± 1900 yrs BP (Fujioka et al., 2014).

The steady decline in Si/Ti regional MCEOF1 scores between ~7500 and 4400 (Figure 7.11) is interpreted to be indicative of slowly decreasing monsoonal precipitation throughout the mid- Holocene by comparison to the early Holocene. Lithogenic elements at the three sites also decline at, or after, ~7000 cal. yr BP, either suggestive of reduced rainfall and runoff in the catchment, or implying the spring mounds had grown above the height affected by deposition from runoff. This decline is less pronounced in ELZ01, which may be a direct result of the less protuberant topography of the spring accumulating alluvial sediment even during periods with reduced runoff. In addition, increasing Ca at this time in the three sites suggest drier conditions during the mid- Holocene, although as previously discussed spring mound growth could also account for this change.

A weaker IASM after 7500 cal. yr BP seems a counterintuitive response to high orbital tilt and precession which favoured the Southern Hemisphere at this time (Wyrwoll et al., 2007). However, the weakening summer monsoon in the Kimberley during the mid-Holocene corresponds with the culmination of deglacial sea level rise (Lewis et al., 2013) and a small northward shift in mean ITCZ position (+0.3 ) at ~6000 yrs BP (McGee et al., 2014). These changes have also been invoked to explain reductions in other Southern Hemisphere monsoon systems such as the South American Summer Monsoon (e.g. Seltzer et al., 2000; Cruz et al., 2005). The mechanisms proposed for this northward shift include a warmer tropical North Atlantic Ocean and reduced albedo in the Northern Hemisphere as a result of increased tropical vegetation cover and decreased high latitude sea ice and snow (Braconnot et al., 2007). Importantly, however, monsoon reconstructions at Flores (Griffiths et al., 2009) and from northern Australian speleothems during the mid- to late-Holocene (Denniston et al., 2013a) are anti-phased. This is despite their close proximity and the fact they had previously been in-phase during H1 and H0 (Denniston et al., 2013a). This anti-phasing behaviour is therefore difficult to attribute to mean changes in ITCZ position. Changes in the behaviour of the IOD have been invoked to explain this anti-phasing between the Flores and Borneo speleothems (Griffiths et al., 2010), however IOD events typically occur during the Austral winter and spring and therefore have limited impact on the Kimberley’s monsoonal rainfall (Taschetto et al., 2011). Consequently, the mechanisms responsible for reduced monsoon activity at this time are not fully understood at present. It is possible that a weakened IASM may also be in response to an increase in the frequency and/or amplitude of El Niño events from ~5000 yrs BP, as has been previously

180 Chapter 7 proposed as a mechanism for reduced monsoonal precipitation seen at this time across tropical Australasia (e.g. Gagan et al., 2004). A similar drying trend is expressed in other Kimberley records including speleothems and offshore sediment cores (Denniston et al., 2013b; Kuhnt et al., 2015), in addition to a number of sites in the tropical zone across the Australasian region (Reeves et al., 2013).

A continued reduction in monsoonal precipitation into the late-Holocene is indicated by a continued decline in Si/Ti regional MCEOF1 scores (Figure 7.11), albeit with a higher frequency of climate variability superimposed on this general drying trend. Also potentially indicative of increasingly dry conditions is the gradual increase in Ca counts within the springs. A similar decrease in moisture is seen elsewhere in the Kimberley and offshore (e.g. van der Kaars et al., 2006; Denniston et al., 2013b). Within the general reduction in moisture availability in the Kimberley during the late- Holocene, a number of short periods of relatively enhanced precipitation are indicated by the spring records. For instance, Si/Ti regional MCEOF1 scores indicate a short period (~400 years) of elevated precipitation centred at ~4200 cal. yr BP. The timing of this increase corresponds with the global “4.2 ka event” (Booth et al., 2005), one of the most severe climatic events of the Holocene. It has been suggested that this was a global event ranging from polar to tropical latitudes (Bond et al., 2001; Thompson et al., 2002) with more than 100 records demonstrating dramatic climatic variability centred at 4200 cal. yr BP with evidence of both wetter and drier conditions in different locations (see Wang et al., 2016 and references within). Although there are limited records of this event from Australia, a period of increased monsoon rainfall is also recorded in the KNI-51 speleothem in the Kimberley between ~5000 – 4000 cal. yr BP with a peak centred at ~4200 cal. yr BP (Denniston et al., 2013b). Similarly there is evidence of increased precipitation at Groote Eylandt in the Gulf of Carpentaria at ~4000 yrs BP (Shulmeister, 1992).

The occurrence of the NPP Pseudoschizaea has been used to infer desiccation, drought, oxidation and warmer climates associated with seasonal drying in a number of studies (Scott, 1992; Carrión and Navarro, 2002; Table 7.3). Following this interpretation, Pseudoschizaea regional MCEOF1 scores imply a period of increased aridity beginning at ~2600 cal. yr BP, peaking at ~2000 cal. yr BP, and prevailing until ~1000 cal. yr BP in the studied springs (Figure 7.12). This is likely associated with a reduction in the intensity of the IASM during this period.

Complex network theory suggests a connection between the IASM and the Laguna Pallcacocha record from southern Ecuador during the late-Holocene (from 3000 yrs BP to present) (McRobie et al., 2015), with the signal in the latter interpreted as indicative of an increased number of moderate- to-strong El Niño events (Moy et al., 2002). McRobie et al. (2015) therefore suggest a possible

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ENSO teleconnection to northwest Australia at this time, despite ENSO only having most impact on monsoonal precipitation in this region at present during strong events, e.g. as the 1982 – 1983 El Niño during which there was a marked reduction in rainfall (Bureau of Meteorology, 2017). The decreased monsoon activity apparent in the spring records corresponds with a similar trend also expressed in other records across the Kimberley (e.g. Denniston et al., 2013b; Haberle, 2015; Vannieuwenhuyse et al., 2017).

The abrupt decline in Pseudoschizaea regional MCEOF1 scores after 1000 cal. yr BP (Figure 7.12), suggests ameliorating conditions to some degree in the Kimberley. This occurs at broadly the same time as a general increase in the accumulation of Glomus and Tilletia at each site (indicative of soil erosion and parasitic fungal activity (Van Geel et al., 1972, 1989; Carrión et al., 1995, 1999; Navarro et al., 2000; Cook et al., 2011; Shumilovskikh et al., 2015; Table 7.3)). Enhanced soil erosion and fungal activity may be a result of increased moisture, but may also be reflective of increases in the Kimberley’s human population during the late-Holocene (Williams et al., 2013). The timing of this climatic amelioration broadly corresponds to a reduction in the number of moderate-to-strong El Niño events interpreted from the Laguna Pallcacocha record (Moy et al., 2002). Rock art from the Wanjina period in the Kimberley also points to increased precipitation in the late-Holocene, where monsoonal iconography such as lightning is incorporated in many of the “classic” Wanjina paintings whilst the Wanjina deities themselves are associated with life-giving rains (Walsh, 1995), the majority of the “classic” Wanjina figures dating from after ~1500 yr BP (e.g. Morwood et al., 2010) (see Section 4.5.1).

In the upper section of the cores (after ~2000 cal. yr BP) increases in Entorrhiza were apparent in the springs. This is likely to reflect root penetration from rushes/sedges currently/recently growing on the site rather than a climatic signal, since this NPP forms galls on the roots of Cyperaceae and Juncaceae (currently found growing across each of the springs) (Riess et al., 2015; Table 7.3).

7.5.2.2 Pollen evidence for site specific spring development

A large degree of dissimilarity occurs between the three pollen records, as demonstrated by the difference in PCA axis 1 scores (Figure 7.10), species composition, and overall trends in vegetation assemblages (Figure 7.7, Figure 7.8 and Figure 7.9). These inter-site discrepancies can be attributed to differences in spring development at each of the three sites as discussed in Section 7.2. For instance, both Black Springs and Fern Pool are classical mound springs, with topographically protuberant mounds of organic detritus, although Fern Pool consists of a series of distinct smaller mounds associated with a number of spring vents. Gap Springs can be described as a spring seep, i.e. it has not formed a protuberant mound (refer to Section 2.5). 182 Chapter 7

As demonstrated in Section 7.5.2.1, elemental geochemistry and NPPs exhibit broadly consistent trends across the three sites, indicative of coherent spatio-temporal changes in the Kimberley’s hydroclimate over the last 14,500 years. However, the local differences in spring development, morphology and vegetation are manifested as diverse responses of the vegetation community at each spring to the same climatic change. For instance, to accumulate a mound of organic material above ground, such as at Black Springs, artesian pressure must sustain a water-table “dome” higher than the surrounding landscape (McCarthy et al., 2010). Therefore it seems likely that during wetter periods, increased recharge will enhance artesian pressure at Black Springs and therefore increase surface water availability. This mechanism could be responsible for the abundant wetland taxa recorded in BSP02 during the late Pleistocene and early-Holocene, as well as the increase in spring taxa at the expense of wetland taxa from the mid-Holocene onwards following the decline in monsoonal precipitation. Alternatively, or in addition, as the mound develops, there is potential for it to grow above the water table dome, which would favour a vegetation community able to exist on the drier mound. Vegetation communities may also be influenced by the build up of organic detritus at the spring, with some species potentially requiring a certain depth of peat or organic content before they are able to establish. Therefore pollen records may reflect spring growth alone.

Gap Springs records roughly the opposite patterns to those in Black Springs, with more abundant spring taxa present during the late-Pleistocene and early-Holocene, and increasing wetland taxa (predominantly Myriophyllum) at the expense of spring taxa (predominantly Pandanus and Melaleuca) in the late-Holocene. Gap Springs has not accumulated an above-ground mound of organic detritus and it is therefore likely that changes in artesian pressure and water availability have been less dramatic at this site by comparison to Black Springs. It is therefore possible that drier conditions result in a more open over-storey at the spring, with a relative increase in wetland taxa at the expense of spring taxa (e.g. in the late-Holocene), and that wetter periods are characterised by dense over-storey cover, reflected by relative increases in spring taxa (e.g. in the early-Holocene).

Unlike Black Springs and Gap Springs, the Fern Pool taxa vary throughout the record. Concretions of TiO/Al2O3, which are typically found in dehydrating conditions (Sherman, 1952), are prominent in the lower portion of this core suggesting that Fern Pool experiences the most extreme water-table fluctuations of the three sites (see Chapter 6; Field et al., 2018). Consequently, it is likely that the fluctuating vegetation trends at this spring are in response to the comparatively larger groundwater fluctuations and the presence of a variety of vegetation communities at multiple spring vents.

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7.5.2.3 Pollen evidence for changes in the landscape surrounding the springs

Despite the discrepancies between the spring vegetation assemblages as described in Section 7.5.2.2, the spring records demonstrate that the vegetation composition of the landscape surrounding each of the three springs is broadly similar. Consequently some general interpretations regarding palaeoclimatic and palaeoenvironmental conditions can be made from these pollen assemblages.

The presence of Eucalyptus in the basal sediments of BSP02 and ELZ01 implies that Tropical Eucalypt Woodland/Grassland (MVG12) was already established in this part of the Kimberley by ~14,500 cal. yr BP and that this vegetation assemblage has prevailed, at least in the northern part of the study region, until present day. In accordance with Southeast Asia, Australia and the Pacific (SEAPAC) biome distribution classifications the pollen results indicate that, for the study region, mean annual precipitation from ~14,500 cal. yr BP to present has ranged between 500 mm/yr and 1100 mm/yr, with temperatures >18 °C (Pickett et al., 2004) albeit with some potential variation during the late-Holocene.

A reduction in the representation of Eucalyptus pollen in the southernmost sites (Fern Pool and Gap Springs) during the late-Holocene at ~2200 cal. yr BP and after 1650 cal. yr BP respectively, is also potentially indicative of a reduction in mean annual precipitation during this period. This change could be consistent with a northward contraction of Tropical Eucalypt Woodland/Grassland (MVG12) and an expansion of drier vegetation communities such as Eucalypt Open Woodlands (MVG3), Tussock Grasslands (MVG19) or Hummock Grasslands (MVG20) which are presently found south of Gap Springs (the southernmost site) (Department of the Environment and Water Resources, 2007). The mean annual precipitation associated with the latter three vegetation groups is currently ≤500 mm/yr (Pickett et al., 2004). Therefore, the reduction of Eucalyptus in Fern Pool and Gap Springs implies a reduction in moisture. Given the existing rainfall gradient across the Kimberley, this reduction could be potentially as much as approximately half current annual totals, i.e. by 500 mm/yr. However, that this reduction in Eucalyptus is only apparent in the southernmost sites suggests that precipitation remained high enough, at least in the northern portion of the study region, to sustain Tropical Eucalypt Woodland/Grassland and that the reduction in rainfall in unlikely to have been of this magnitude. Additionally, given that Eucalyptus is still present at this time (albeit in small amounts) no firmer claims are made. Finally, during the last ~1000 years an increased representation of Eucalyptus at Fern Pool may imply the southward expansion of Tropical Eucalypt Woodland/Grassland (MVG12) and mean annual precipitation of ≥500 mm/yr.

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Figure 7.14. Conceptual environmental and hydroclimatic change in the Kimberley from the late Pleistocene to present: A) Pre-14,500 cal. yr BP with inactive monsoon conditions; B) 14,500 – 11,000 cal. yr BP with active but weak summer monsoon conditions, weak runoff, onset of spring activity and the accumulation of detrital material at the juvenile springs. Note, Tropical Eucalypt Woodland/Grassland (MVG 12) is established at least by this period; C) 11,000 – 7500 cal. yr BP with enhanced summer monsoon activity, increased runoff and recharge of aquifers. This leads to intensified spring discharge; D) 7500 – 2600 cal. yr BP with a weakening summer monsoon and reduction in runoff, recharge and spring discharge; E) 2600 – 1000 cal. yr BP with a very weak or absent summer monsoon and the possible northward contraction of Tropical Eucalypt Woodland/Grassland (MVG 12) and expansion of drier vegetation communities; and F) 1000 cal. yr BP to present with ameliorating climatic conditions and a more active summer monsoon, resulting in runoff, recharge, and spring discharge

7.6 Conclusion

The use of PCA and MCEOF analysis enabled the identification of regional trends (i.e. >1000s km2) from three multi-proxy datasets, some of which reflected site-specific conditions only. Specifically, the coherency between the Itrax µXRF and NPP datasets at the three studied springs enabled a reconstruction of spatio-temporal changes in the hydroclimate of tropical northwest Australia since the late Pleistocene. The regional-scale reconstruction of IASM activity from the Kimberley presented here is in agreement with reconstructions from elsewhere within the tropical Australian region. For instance, these records indicate that monsoonal precipitation increased from ~14,500 cal. yr BP and further intensified at 12,000 cal. yr BP, before peaking in the early Holocene (~11,000 cal yr BP until 7,500 cal. yr BP). Within the study region, mean annual precipitation throughout this period probably ranged between 500 – 1100 mm/yr. Whilst there is possible increase in IASM activity corresponding with periods of Northern Hemisphere cooling (e.g. towards the end of H0), this is subtle and there are no patterns of millennial scale change expressed as clearly as interpreted from speleothems in the Kimberley (Denniston et al., 2013a). These records indicate that the IASM weakened across northwest Australia from ~7500 cal. yr BP, however there were periods of variability superimposed on this trend, some of which are not explicitly noted in other records from the wider IASM region. For instance, at ~4200 cal. yr BP there is a brief return (~400 years) to more active monsoon conditions corresponding with the global 4.2 ka event. Finally, these records express a weakening of the monsoon from 2600 cal. yr BP, particularly between 2000 – 1000 cal. yr BP, before ameliorating somewhat over the last 1000

186 Chapter 7 years. This period of drier conditions is possibly linked to an increase in the frequency and/or intensity of El Niño events, during which it is possible that the Kimberley’s Tropical Eucalypt Woodlands/Grasslands contracted northwards with mean annual precipitation (at least in the southern portion of the study region) potentially falling below 500 mm/yr.

Significant inter-site differences were observed between the three springs, notably within the pollen and micro-charcoal datasets. These can primarily be attributed to complex site-specific morphological and vegetation differences. Whilst these proxies provide valuable palaeoenvironmental information, overall this study attests to the benefits of a multi-site, multi- proxy approach, avoiding the pitfalls of potentially over-interpreting a single record. In particular, this research highlights the importance of a comprehensive understanding of site characteristics, and suggests that reconstructions from single sites should generally be treated with caution.

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8 Conclusions and future research directions

This chapter summarises the outcomes of this thesis, and how they have addressed each of the aims and objectives presented in Chapter 1. The findings are discussed here in the context of how this research has contributed to knowledge of late Quaternary climate and environmental change in the Kimberley from the LGIT, and how organic spring deposits can be used to investigate such changes. This chapter also assesses the limitations of this thesis, and provides recommendations for future research directions.

8.1 Problem statement and research aims

This thesis has presented new records of late Quaternary climatic and environmental change for northwest Australia. Specifically, the research developed new proxy-records from the Australian savanna, a region identified by the OZ-INTIMATE group as requiring further research (Reeves et al., 2013). It successfully addressed some major deficiencies in knowledge of long-term environmental and climatic change in this region, and variability of the IASM over long timescales. This research also advances understanding of how organic spring systems behave, and has developed a new methodology for utilising organic spring deposits as archives of palaeoenvironmental records. This is particularly important for arid and semi-arid environments, and/or where there is a strong seasonal precipitation regime such as the Kimberley, as establishing high-resolution records of change in these environments is challenging due to the lack of “conventional” archives that preserve robust sedimentary records (e.g. lakes and extensive perennial wetlands). Chapter 1 outlined the rationale for conducting the research presented in this thesis, including a statement of research problems relevant to developing understanding of late Quaternary change in the Kimberley and using organic spring deposits to do so:

 There is a growing requirement to understand long-term climate variability in northwest Australia to provide context for the changes observed in rock art styles and the archaeological record, and sparse knowledge of long-term monsoon dynamics in this region limiting understanding of past climate systems and their impacts;  There are scarce continuous, high-resolution records of palaeoclimatic and palaeoenvironmental change from the Kimberley;  There is a lack of “classic” archives of palaeoenvironmental/palaeoclimate conditions in the Kimberley e.g. lakes and extensive wetlands due to the extreme seasonality in the region. Those records that do exist may be compromised by chronological hiatuses, oxidation and unconformities due to climatic variability; and

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Six research aims were identified to address these problems:

1. To develop knowledge of the Kimberley at present to construct a framework for understanding past changes;

2. To assess the current state of understanding regarding late Quaternary (<50,000 yr BP) climate and environmental change in the Kimberley in order to identify knowledge gaps;

4. To reconstruct climate and environmental change in tropical northwest Australia during the period spanning the LGIT to present day;

5. To assess whether the Kimberley has experienced changes in past climate and environmental conditions on a regional-scale (i.e. >1000s km2); and

6. To relate changes in the Kimberley’s climate and environment since the LGIT to potential drivers of climatic variability.

The following section outlines how these aims were addressed through a number of research objectives.

8.2 Research findings

8.2.1 Aim 1: To develop knowledge of the Kimberley at present to construct a framework for understanding past changes:

The first research objective was addressed to achieve this aim, which was to review the Kimberley’s current climate, geology, hydrology and environments, including the distribution of known organic spring deposits. This objective is presented as a review in Chapter 2 which identified the location of organic springs suitable for developing new palaeo-records. The information in this review provided the basis for the three springs selected for analysis in Chapters 5 – 7 (Black Springs, Fern Pool and Gap Springs).

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The review also provided a summary of the Kimberley’s current climate, geology, hydrology and environments. Information from this summary was then used for interpretation of the records presented in Chapters 5 – 7. Key information identified as relevant to these interpretations include:

- A precipitation gradient is present across the Kimberley (including within the study region), with precipitation derived primarily from the IASM and tropical cyclones; - Modern variations in IASM activity are predominantly driven by the seasonal migration of the ITCZ, the MJO, SSTs and drivers of SSTs including ENSO, El Niño Modoki events, and (to an extent) the interaction of ENSO with the IOD; - The hydro-geology of the study region is comprised of the sedimentary rocks of the Kimberley Plateau. These sedimentary rocks recharge local aquifers within the Kimberley’s fractured rock province, providing groundwater to the springs within this thesis; and - The vegetation surrounding the springs is primarily classed as Tropical Eucalypt Woodlands/Grasslands (MVG 12). To the south of the springs vegetation is classed as Eucalypt Open Woodlands (MVG 3), Hummock Grasslands (MVG 20) and Tussock Grasslands (MVG 19).

8.2.2 Aim 2: To assess the current state of understanding regarding late Quaternary (<50,000 yr BP) climate and environmental change in the Kimberley in order to identify knowledge gaps:

This aim was achieved through addressing research objectives 2 and 3. Objective 2 was to review existing published records of late Quaternary environmental and climatic change in the Kimberley and offshore. Objective 3 was to assess existing archaeological and rock art data, alongside literature regarding Aboriginal mythology, to gather additional evidence of human-environmental interactions in the region. These objectives are presented as literature reviews in Chapters 3 and 4, with a synthesis of climatic and environmental change in the Kimberley over the last 50,000 years presented in Chapter 3, and a synthesis of human and environment/climate interactions over the same timeframe presented in Chapter 4. These syntheses highlighted that there are a number of records in the Kimberley and offshore which can be used to infer past changes, which were then related to interpretations from the new records developed in Chapters 5 and 7. Existing records include additional lines of evidence from rock art, archaeology and Aboriginal mythology. However, the vast majority of these records are of a low-temporal resolution, discontinuous, contain information limited to sea level change, or have poorly constrained chronologies. There are also issues inherent with a number of these records, for instance where marine sediment cores are assumed to reflect terrestrial changes. Furthermore, some records provide conflicting information.

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In order to develop a comprehensive understanding of climate and environmental change in the Kimberley from the LGIT to present, and to address the discrepancies that exist between some records, high-resolution, continuous records with robust chronologies are required. The syntheses presented in Chapters 3 and 4 indicated that, at present, such records are unavailable. Whilst there are a handful of high-resolution records, they contain hiatuses or are too short to span the required timeframe (the LGIT). This provided justification for the development of the new, high-resolution and continuous records in the thesis (presented in Chapters 5 and 7).

8.2.3 Aim 3: To ascertain whether organic spring deposits are suitable archives for reconstructing climatic and environmental change in otherwise challenging environments such as the Kimberley (e.g. arid and semi-arid regions):

Research objectives 4, 5 and 6 were addressed to achieve this aim. The fourth research objective was to develop new records of environmental and climatic change over the last ~14,500 years, and in doing so ascertain whether organic spring deposits in the region contain proxies amenable to palaeoenvironmental/climatic research. An initial ~15,000 year record was developed from Black Springs (core BSP00) and is presented in Chapter 5. This record utilised pollen, micro-charcoal, sedimentary characteristics, and peat humification to provide the first high-resolution palaeoenvironmental reconstruction for the Kimberley encompassing the entire Holocene period and potentially extending into the late Pleistocene. The research confirmed that organic spring deposits in Australia’s northwest contain proxies suitable for palaeoenvironmental research. However, there were some complications with the 14C chronology for this record, with age-depth reversals in the lower part of the record limiting the reliability of the palaeoenvironmental interpretation from this section. This indicated that further work was required to assess the suitability of organic spring deposits as archives.

Objective 5 was therefore to identify the limitations of organic spring deposits as palaeoenvironmental and palaeoclimate archives. In order to achieve this, all existing records from organic spring deposits in a number of global locations were reviewed, including isolated springs in dryland environments and springs within larger mire complexes. This review is presented in Chapter 6, and indicated that chronologies from these archives overwhelmingly relied on 14C dating, although the vast majority of existing 14C chronologies were complicated by age-depth reversals or erroneously young dates. Based on this review, a model of conceptual pathways of geochronological complexity in these settings was developed.

Objective 6 was therefore to develop a protocol for building robust chronologies in these archives. This is critical since organic springs are located within the Kimberley and offer an alternative for 191 Chapter 8 developing continuous, high-resolution records of environmental change in a region where there is a lack of “classic” archives (e.g. lakes and extensive wetlands) due to extreme seasonality. In order to better understand the behaviour of 14C and other radionuclides used in geochronology within organic springs, and to develop an effective methodology for building robust chronologies in these settings, this thesis utilised multiple geochronological methods on sediment cores from the three springs (Black Springs, Fern Pool and Gap Springs). The results of this geochronological investigation are presented in Chapter 6. These methods included 14C dating of different carbon fractions (bulk organics, roots, SPAC, pollen, and macro-charcoal) utilising a number of pre- treatment techniques (AAA and HyPy), alongside 210Pb dating, the application of 239+240Pu, as well as novel, high spatial resolution, luminescence techniques (Ln/Tn signals). Analysis revealed that in these complex hydro-geological settings, there are multiple sources of contamination which can convolute 14C chronologies. It highlighted that when building 14C chronologies for organic spring deposits not one single carbon fraction appears universally reliable, however that SPAC isolated by HyPy gives reliable 14C dates in the deposits of well-developed springs. This research also indicated that using 210Pb dating for recent spring sediments is unlikely to be successful due to upwelling groundwater in these systems which introduces the potential for uranium enrichment of the sediments. This work therefore provided viable chronologies for not only Black Springs, Fern Pool, and Gap Springs, but also demonstrated that organic spring deposits are suitable archives for reconstructing climatic and environmental change in otherwise challenging environments such as the Kimberley. Furthermore, the research suggested that caution should be exercised when interpreting age models from similar organic spring records where pollen, charcoal or bulk organic samples have been used for 14C dating. Finally, the methodology developed by this research is not exclusive to organic springs and is widely applicable to other settings (e.g. environments with water table fluctuations or deep root growth) and will enable researchers to build more reliable chronologies in both organic springs and other complex hydro-geological settings.

8.2.4 Aim 4: To reconstruct climate and environmental change in tropical northwest Australia during the period spanning the LGIT to present day, and relate changes to potential drivers of climatic variability:

This aim was achieved through research objective 4. As described above, the fourth research objective was to develop new records of environmental and climatic change over the last ~14,500 years using organic spring deposits in the Kimberley. New records were developed from three organic springs located on a ~100 km north-south transect (Black Springs, Fern Pool, and Gap Springs). An initial record developed from core BSP00 from Black Springs (collected in 2005) is

192 Chapter 8 thought to extend to ~15,000 yrs BP, and is presented in Chapter 5. Based on the chronological issues with this core (BSP00) (see Sections 5.5.3 and 8.2.3) this spring was re-sampled in 2015 (core BSP02) and analysed for pollen, micro-charcoal, NPPs, and elemental geochemistry, alongside cores from Fern Pool (FRN02) and Gap Springs (ELZ01). The results of these analyses are presented in Chapter 7. The robust chronologies developed in Chapter 6 indicated that these three cores spanned the timeframe required, extending to ~14,500 yrs BP. These records together demonstrate that precipitation in the Kimberley slowly increased from ~14,500 cal. yr BP, with monsoon activity intensifying from ~12,000 cal. yr BP. The monsoon was particularly active in northwest Australia during the early-Holocene (~11,000 – 7500 cal. yr BP) before precipitation gradually decreased from 7500 cal. yr BP. A short-lived increase in monsoon activity is noted around the mid-late-Holocene transition centred at ~4200 cal. yr BP, before a sustained weakening of the monsoon between 2600 – 1000 cal. yr BP with a particularly arid phase between 2000 – 1000 cal. yr BP.

8.2.5 Aim 5: To assess whether the Kimberley has experienced changes in past climate and environmental conditions on a regional-scale (i.e. >1000s km2):

Whilst palaeoenvironmental records were developed from three springs in the Kimberley (as described in Chapter 7 and Section 8.2.4), it is important to assess whether changes within the records are representative of a wider spatial area since a number of studies have demonstrated that this is not always the case. Research objective 7 was therefore addressed to achieve this aim, which was to compare climatic and environmental records spanning the last ~14,500 years in the Kimberley. This comparison utilised the three records developed from Black Springs, Fern Pool and Gap Springs presented in Chapter 7 (the outcome of objective 4). PCA axis 1 scores indicated that whilst the NPPs and elemental geochemistry followed similar trends across the three sites, pollen did not. The shared trends in NPPs and elemental geochemistry, however, implied spatio-temporal coherency between the three sites. On this basis, MCEOF analysis was performed on two proxies from each of the datasets: Pseudoschizaea (a NPP indicative of seasonal desiccation and drought); and Si/Ti ratios (a proxy for moisture availability and therefore precipitation). MCEOF analysis demonstrated reliably shared trends across the three sites in these two proxies, and as such provided a regional-scale reconstruction of climatic change in the Kimberley over the last ~14,500 years. The inter-site differences within the pollen and micro-charcoal records are likely to be due to local morphological and vegetation differences. This thesis therefore highlighted the importance of understanding local site dynamics, and using multiple sites and multiple proxies within a landscape

193 Chapter 8 to avoid over-interpretation of records and elucidate genuine regional-scale (i.e. >1000s km2) environmental and climatic change.

8.2.6 Aim 6: To relate changes in the Kimberley’s climate and environment since the LGIT to potential drivers of climatic variability.

This aim was achieved by addressing the eighth and final research objective, which was to identify potential drivers of climatic variability since the LGIT, and analyse the spatial and temporal changes interpreted from the records presented in Chapters 5 and 7 in the context of these drivers. Current drivers of monsoon variability in northwest Australia are presented in Section 2.4. These include the seasonal migration of the ITCZ, the IPWP, the MJO, and drivers of SSTs such as ENSO and El Niño Modoki events, including interactions of ENSO with the IOD (despite the IOD having little direct impact on monsoon activity). A discussion of the literature (embedded within Chapters 5 and 7) indicated that since the LGIT these drivers have been affected by variations in sea level, teleconnections, and insolation. The potential drivers of the changes interpreted from the records are therefore presented in Chapters 5 and 7.

The research links the increase in monsoonal precipitation at ~14,500 cal. yr BP to deglacial sea level rise and the flooding of the Sunda shelf. This would have intensified tropical convection and moisture advection over the IASM region. The further intensification of precipitation from ~12,000 cal. yr BP is proposed to have been driven by a southward “push” of the ITCZ as a result of Northern Hemisphere cooling during H0, with this push possibly accentuated by greenhouse gas warming following the ACR. Active monsoon conditions during the early Holocene are linked to continued sea level rise and increasing connectivity between all IPWP seaways, compounded warmer SSTs in parts of IPWP as a result of insolation-induced heating in the Northern Hemisphere. These warmer SSTS, coupled with high orbital tilt, would have facilitated moisture advection and convection over northern Australia and produced strong monsoon flow at this time. The reduction in monsoonal precipitation from ~7500 cal. yr BP is proposed to have been driven the culmination of deglacial sea level rise and potentially by a small northward shift of the ITCZ. Whilst the drivers of the short return to wetter conditions centred at 4200 cal. yr BP are not fully understood at present, this thesis notes that the timing of this increase in monsoon activity is in concert with the global 4.2 ka event, one of the most severe climatic events of the Holocene. The decrease in monsoon activity during the late Holocene, particularly between 2600 – 1000 cal. yr BP, is proposed to have been driven by increased ENSO variability and amplitude, with a greater teleconnection between ENSO and northwest Australia believed to have been present at this time (McRobie et al., 2015). Finally, a reduction in the number of moderate-to-strong El Niño events

194 Chapter 8 over the last ~1200 years is invoked to explain the ameliorating climatic conditions within the last millennium.

8.3 Contribution of this research

The contribution and implications of this research are described in the context of the problem statement outlined in Chapter 1 and repeated in Section 8.1.

The first high-resolution records of palaeoenvironmental and climatic change for northwest Australia which encompass the entire Holocene and extend into the late Pleistocene, covering the LGIT, are presented in this thesis (Chapters 5 and 7). The research also provided confirmation that long term changes interpreted from these records were regional in extent. Therefore these new records now provide context for changes in the archaeological and rock art records of the Kimberley for at least the last ~14,500 years. This is important given the volume of ongoing archaeological research in this region. Furthermore, the new records presented here have improved knowledge of the activity of the IASM over the last ~14,500 years. These records of monsoon activity can now be compared to and linked with other records from the greater IASM region (e.g. Borneo and Indonesia), and of the wider monsoon system which incorporates the EASM.

 There are scarce continuous, high-resolution records of palaeoclimatic and palaeoenvironmental change from the Kimberley.

As outlined in Chapter 3, there are a limited number of high-resolution records of palaeoclimatic and environmental change in northwest Australia (e.g. McGowan et al., 2012; Proske et al., 2014; Proske, 2016; Denniston et al., 2013a, 2013b, 2015). However just three of these are continuous (McGowan et al., 2012; Denniston et al., 2013b, 2015). This research increases the number of continuous, high-resolution records from the Kimberley from three to six, whilst at the same time extending the time-span covered by these records from ~9000 cal. yr BP to ~15,000 cal. yr BP.

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Whilst there are lack of “classic” archives for palaeoenvironmental research in the Kimberley, which has to date contributed to the scarce number of high-resolution, continuous records (outlined above and in Chapter 3), this thesis has confirmed that organic spring deposits have the potential to provide outstanding records of palaeoenvironmental and climatic change. It is therefore evident that organic spring deposits are a viable alternative which can provide sedimentary records analogous to more conventional archives. This is of particular importance within arid and semi-arid regions where there is generally a lack of high-resolution, continuous records due to the lack of “classic” archives (e.g. inland Australia, South Africa, Kenya and Jordan).

The thesis confirmed that organic spring deposits are complex hydro-geological settings, with numerous pathways through which geochronological complexity may be introduced. As outlined in Chapter 6, this has resulted in the confusing 14C chronologies exhibited by the majority of records previously developed from organic spring deposits. The research presented here demonstrates that targeting pollen, macro-charcoal or bulk organics when constructing 14C chronologies in organic spring deposits is likely to give unreliable results, although SPAC isolated by the HyPy pre- treatment will give robust 14C dates in the deposits of well-developed springs. Recommendations provided include considering factors such as the organic content of spring sediments, local hydrological conditions, and geology prior to attempting 210Pb dating, as post-burial uranium enrichment may mean it is not always be possible to build successful 210Pb chronologies. The methodology presented in the thesis for building reliable chronologies in organic spring deposits confirms the outstanding potential of these archives which will facilitate their use in future palaeoenvironmental research.

8.4 Thesis limitations

The limitations of this research relate to three main areas which include: 1) the temporal resolution of some of the datasets; 2) the discrepancy between the length of the records presented here and the length of human occupation in the Kimberley; and 3) the qualitative nature of the palaeoenvironmental and palaeoclimatic interpretations.

1. The pollen, NPP and micro-charcoal datasets presented in Chapter 7 are of a relatively coarse temporal resolution (~600 years) since they are primarily used in this thesis for the

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purposes of inter-site comparisons to disentangle regional-scale vs. local trends. As a result, it is not possible to use these datasets from the cores BSP02, FRN02 and ELZ01 to determine centennial or sub-centennial scale environmental change. By comparison, the Itrax datasets from these cores (presented in Chapter 7), and the pollen and micro-charcoal datasets presented for core BSP00 (presented in Chapter 5) are of a higher resolution (~6 – 12 years, and ~140 years respectively). Therefore, despite the lower temporal resolution of the pollen, NPP and micro-charcoal datasets from BSP02, FRN02 and ELZ01, it has still been possible to discern climatic and environmental change over shorter timescales in this thesis (e.g. in the late Holocene). 2. The basal ages of the new records presented in this thesis range from the LGIT to present (spanning ~14,500 years). The basal ages of ~14,500 yr BP are likely due to the location of the study sites within the Kimberley’s fractured rock province. As outlined in Chapter 2, the aquifers within this province are recharged locally and immediately by precipitation. Given that the palaeoenvironmental reconstructions presented in Chapters 5 and 7 indicate that monsoonal precipitation increased from ~14,500 cal. yr BP, this would have had the effect of elevating or instigating spring discharge and sedimentation at this time. Whilst the records presented here do not extend into the LGM, records from elsewhere in the region suggest that the monsoon was far weaker at this time (see Chapter 3). The lack of sediment preserved prior to ~14,500 cal. yr BP at the springs can therefore be interpreted as the likely result of a less active monsoon. Although understanding changes during and since the LGIT is particularly important since it is arguably the most significant transition in global climate of the late Quaternary (Reeves et al., 2013), the Kimberley has a long history of human occupation spanning ~50,000 years, with a growing body of archaeological and rock art research. Due to the nature and location of the springs used in this research, this thesis therefore cannot provide context for the entire period of human occupation. Furthermore, there are several discrepancies between existing Kimberly records (outlined in Chapter 3) which are beyond the timeframe of the records presented here and cannot be resolved by this research.

3. With the exception of the interpretations regarding precipitation presented in Section 7.5.2.1, the reconstructions of environmental and climatic change presented in this thesis are primarily qualitative in nature. For instance, climate during time slices (e.g. the early- Holocene) is described in general terms in relation to the preceding interval, for instance as “wetter”, “drier”, “cooler”, “warmer”, or that the monsoon was “more/less active”. This

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thesis is therefore only able to provide a broad insight into the region’s climate and its temporal variability.

8.5 Future research priorities

Areas which require future research are identified below, which are related to a number of the limitations of this thesis presented in Section 8.4. They include:

1. Developing high-resolution palaeoenvironmental and palaeoclimate records from the Kimberley’s terrestrial environments which encompass the entire period of human occupation (~50,000 years), or at least extend from 14,500 – 50,000 yrs BP. This research is required to address the discrepancies between a number of records from the region, for instance during late MIS3 (50,000 – 30,000 yrs BP) and the LGM (21,000 – 18,000 yrs BP) as outlined in Chapter 3. This research is also essential in providing context for the archaeological and rock art record for the entire duration of human occupation in Australia’s northwest.

Whilst this thesis has proven that organic spring deposits are valuable high-resolution archives for palaeoenvironmental and palaeoclimate research, the springs within the Kimberley’s fractured rock province are unlikely to contain records that encompass the entire period of human occupation due to their dependence on locally and immediately recharged aquifers. Particular attention should therefore be given to exploring a variety of other locations and archives within northwest Australia. As outlined in Section 2.2, organic spring deposits are also located within the Kimberley’s large sedimentary basins (e.g. the Canning and Bonaparte Basins) which are associated with extensive and productive aquifers. Palaeoenvironmental research from Australia’s Great Artesian Basin demonstrates that extensive groundwater systems can support spring activity even during periods of reduced rainfall, with records developed from this region which encompass the last glacial period (e.g. Dodson and Wright, 1989; Fluin et al., 2013) and far beyond (e.g. Love et al., 2013). It is therefore feasible that organic springs located within the Kimberley’s Canning and Bonaparte Basins may contain records which extend past the LGIT, and these should be targeted in future research endeavours.

Other promising archives for high-resolution palaeoclimatic research within the Kimberley include speleothems, given that a long record has previously been derived from Ball Gown Cave in the Napier Range (Denniston et al., 2013a). Tufas, another secondary limestone deposit, also have the potential to provide high-resolution archives of change since they

198 Chapter 8

contain a number of proxies including fossilised algae, insect larvae, pollen, cyanobacteria, and stable isotopes (Carthew et al., 2003; Andrews, 2006). Research on tufas located in northwest Queensland indicates that accumulation occurred during the LGM, deglacial and early-Holocene (Drysdale and Head, 1994), and whilst similar deposits have been located in the Kimberley in the Napier and Oscar Ranges they are yet to be investigated (Wright, 2010; Viles and Goudie, 1990). These deposits therefore also have the potential to contain long, high-resolution records of change in northwest Australia, and should be given attention in future.

Finally, unpublished data from the Mitchell Plateau indicates that sediment cores extracted from palaeochannels preserve high-resolution records which extend into the last glacial (Haberle, 2015). Whilst these archives frequently contain hiatuses (Haberle, 2015), these locations potentially offer another avenue for extending the existing timeframe of palaeoenvironmental research in the Kimberley.

2. Developing quantitative palaeoclimate records for the Kimberley. This research is essential in understanding the climate of the region during the late Quaternary, enabling real insight into the “weather” experienced by Aboriginal populations during this time. Such information would provide an in-depth context for the archaeological and rock art records. Furthermore, quantitative palaeoclimate data will improve overall understanding of the global climate system, given the links between the IASM and the wider monsoon system including the EASM and IPWP, and the accuracy of global climate models. This quantitative analysis may be achieved by approaches such as transfer functions, provenancing of aeolian dust, and numerical palaeoclimate modelling, and should be given more attention in future. Whilst this has been attempted for marine records off northwest Australia (van der Kaars et al., 2006), no fully quantitative palaeoclimate records for the Kimberley’s terrestrial environments yet exist.

8.6 Summary

Despite the difficulties in developing high-resolution records of climatic and environmental change in the interior regions of Australia’s tropical north, this thesis has succeeded in developing three new high-resolution records from the Kimberley in Australia’s northwest. These records span up to ~15,000 years, and provide a regional-scale (i.e. >1000s km2) reconstruction of monsoon activity since the LGIT. This thesis has also developed an approach for using organic spring deposits as alternative archives in challenging regions such as the semi-arid and arid environments in Australia’s tropics. 199 Chapter 8

It is envisaged that these reconstructions will provide valuable context for the archaeological and rock art record in the region, and increase understanding of the IASM system over long timescales. The methodology for working with records derived from organic springs outlined in this thesis will also enable researchers in other arid and semi-arid regions to successfully build robust chronologies for their archives, and can be applied to a number of other settings which experience deep root growth and/or groundwater fluctuations. However, there is scope to build on this work by extending the length of the high-resolution records in the Kimberley, and by generating quantitative data on the region’s palaeoclimate.

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Appendices

Appendix 1. Submitted journal articles during candidature

Field, E., Tyler, J., Gadd, P., McGowan, H., Marx, S., in review. Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years. Quaternary Science Reviews. Incorporated as Chapter 7.

Contributor Statement of contribution Emily Field (Candidate) Conception and design (85%) Laboratory analyses (90%) Statistical analyses (50%) Wrote the paper (100%) Edited the paper (65%) Field work (40%) Jonathan Tyler Conception and design (10%) Statistical analyses (50%) Edited the paper (10%) Patricia Gadd Laboratory analyses (10%) Edited the paper (10%) Patrick Moss Edited the paper (5%) Hamish McGowan Edited the paper (5%) Field work (30%) Sam Marx Conception and design (5%) Edited the paper (5%) Field work (30%)

236

Appendix 2. Locations of samples mentioned in the text

Sample ID Latitude Longitude Sample type BSP00 -15.633 126.389 Core BSP02 -15.634 126.390 Core D4 -15.634 126.390 Surface ELZ01 -16.404 126.134 Core FRN02 -15.937 126.284 Core MP0 -15.634 126.390 Surface MP1 -15.634 126.390 Surface MP2 -15.634 126.390 Surface MP3 -15.633 126.391 Surface

237

Appendix 3. Pollen (%), micro-charcoal and NPP (concentration and accumulation rates) data for all samples mentioned in the text

BSP00

Depth (cm) 0.3 2.0 4.8 6.2 8.4 10.4 12.3 14.2 16.5 18.6 22.5 23.5 24.6

Acacia 0 0 0 0 0 0 0 0 0 0 0 1.2 0 ACANTHACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 AMARANTHACEAE undif. 0 0 0 0 0 0 2.8 0 0 0 0 8.5 0 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 0 0 2.6 0 0 0 0 0 0 0 0 0 ASTERACEAE 0 0 0.8 0 0 0 0 0 0 0 0 0 2.2 BRASSICACEAE 0 0 0 0 0 0 0.7 0 0 0 0 0 0 Breynia cernua 0 0 0 0 0 0 1.4 0 0 0 0 1.2 0 Callitris 1.5 1.3 0 1.3 0 0 0 0 0 0 0 0 2.2 Casuarina 1.5 1.3 1.5 0 0 0 0 0 0 0 0 0 0 CHENOPODIACEAE 0 0 0 2.6 0 1.2 0 0 0 0 0 0 0 Codonocarpus cotinifolius 0 0 0 0 1.2 0 0 5.1 0 0 0 1.2 0 Colocasia esculenta 0 0 0 0 0 0 2.1 0 0 0 0 0 0 Cycnogeton dubium 43.1 71.8 27.7 35.1 64.6 62.4 4.1 48.7 20.6 28.6 9.1 4.9 6.5 CYPERACEAE 0 1.3 2.3 2.6 2.4 2.4 2.1 0 6.3 0 9.1 0 2.2 Dodonaea 0 0 0 0 0 0 1.4 2.6 0 0 0 4.9 0 Elaeocarpus 0 0 0 1.3 0 0 0 0 0 0 0 2.4 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0 0 0 0 0.7 0 0 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 1.2 0 Ficus 1.5 1.3 0.8 5.2 0 1.2 0 0 0 0 0 1.2 0 Gomphrena 0 0 0 0 0 0 0 0 0 0 0 2.4 0 Mallotus 0 0 0 0 0 0 0 0 0 0 0 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 0 1.3 6.9 6.5 1.2 2.4 4.1 2.6 3.2 0 9.1 2.4 4.3 Myriophyllum 0 0 0 0 0 0 0 0 0 0 0 1.2 0 MYRTACEAE 6.2 1.3 10 7.8 4.9 8.2 10.3 5.1 14.3 14.3 9.1 19.5 21.7 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 4.6 6.4 10.8 6.5 6.1 5.9 6.2 5.1 9.5 0 0 6.1 19.6 Plantago 1.5 0 0 0 0 0 0 0 0 0 0 2.4 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 38.5 14.1 37.7 28.6 18.3 16.5 17.9 30.8 46 57.1 63.6 36.6 41.3 Podocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 1.5 0 0 0 1.2 0 0.7 0 0 0 0 1.2 0 Timonius timon 0 0 0 0 0 0 45.5 0 0 0 0 0 0 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 0 0 1.5 0 0 0 0 0 0 0 0 1.2 0 Typha 0 0 0 0 0 0 0 0 0 0 0 0 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 77.1 84.4 20.5 43.8 641.1 230.4 704.9 833.9 108.4 819.7 886.0 246.4 41.7 (particles per cm3 x 100,000) Pollen concentration (grains 64.5 542.0 78.9 84.5 58.9 73.8 20.3 42.8 23.5 14.6 57.3 22.8 9.9 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 0.0 0.0 559.7 0.0 0.0 0.0 0.0 1111.9 0.0 cm3)

238

Depth (cm) 25.6 27.0 28.0 29.0 30.0 31.1 32.3 33.4 34.5 35.6 36.7 37.8 38.8

Acacia 0 0 0 0 0 0 0 0 0 0 0 0 0.4 ACANTHACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 AMARANTHACEAE undif. 5.4 0 6.4 0 0 2.1 0 0 1.8 0 0 0 14.5 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 0 0 0 0 0 0 0 0 6.5 0 0 0.9 ASTERACEAE 0 0 2.1 0 3.6 0 0 0 0 0.5 1.1 4.3 1.3 BRASSICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Breynia cernua 0.7 0 0 0 0 0 0 0 5.4 0 0 0 0 Callitris 0 5.9 2.1 8.3 0 0 0 3.3 3.6 3.2 0 4.3 1.8 Casuarina 2 0 0 0 0 0 0.9 0 0 0.5 0 0 0.9 CHENOPODIACEAE 0 0 0 0 1.8 0 0 0 0 0 0 0 0 Codonocarpus cotinifolius 0 0 0 0 0 2.1 0 0 0 0 2.2 0 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 3.4 0 7.4 0 3.6 0 2.8 3.3 3.6 3.8 5.6 13 3.5 CYPERACEAE 3.4 0 4.3 8.3 5.4 20.8 3.8 0 10.7 3.2 6.7 0 6.2 Dodonaea 0.7 0 1.1 0 0 0 2.8 0 0 0 2.2 0 1.3 Elaeocarpus 0 0 0 0 0 0 0 0 0 0.5 0 0 0.4 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0.7 0 0 0 0 0 0.5 0 0 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Ficus 2.7 0 1.1 0 0 0 2.4 0 1.8 1.1 1.1 0 3.5 Gomphrena 1.4 0 0 0 0 0 0.9 0 1.8 0 1.1 0 0 Mallotus 2 0 0 0 0 0 1.4 0 0 0 0 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 4.8 11.8 7.4 25 12.5 12.5 4.7 6.7 7.1 13.4 5.6 21.7 4.8 Myriophyllum 0 0 0 0 0 0 0 0 0 0 0 0 0.9 MYRTACEAE 9.5 5.9 19.1 25 19.6 12.5 16 6.7 14.3 18.8 12.4 8.7 10.1 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 18.4 17.6 9.6 0 7.1 22.9 27.8 13.3 19.6 21 22.5 0 18.1 Plantago 4.8 0 1.1 0 0 0 0 0 0 0 0 0 0.9 Plectranthus congestus 0 0 0 0 0 0 1.4 0 0 0 0 0 0 POACEAE 36.7 47.1 37.2 33.3 46.4 25 32.1 66.7 28.6 23.1 32.6 43.5 22 Podocarpus 1.4 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 5.9 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 1.4 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0.7 5.9 0 0 0 0 0 0 1.8 3.2 0 4.3 0.4 Timonius timon 1.4 0 1.1 0 0 0 0.9 0 0 0 4.5 0 6.6 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 0 0 0 0 0 0 0 0 0 1.1 2.2 0 0.9 Typha 0 0 0 0 0 2.1 0 0 0 0 0 0 0.4 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 666.0 458.7 420.2 76.1 106.8 194.9 202.4 30.4 218.4 5.2 118.9 127.9 164.3 (particles per cm3 x 100,000) Pollen concentration (grains 37.8 15.4 29.7 4.0 44.2 30.3 51.4 9.8 36.5 4.4 33.7 3.0 66.7 per cm3 x 1000) Pseudoschizaea concentration (structures per 1544.3 0.0 2211.2 0.0 0.0 1895.3 969.7 0.0 1303.0 0.0 11371.6 0.0 19673.5 cm3)

239

Depth (cm) 39.8 40.9 41.8 42.8 43.8 44.8 46.8 47.7 48.7 49.8 50.8 52.0 53.1

Acacia 0 0 0 0 0 0 0 0 0 0 0 0 0 ACANTHACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 AMARANTHACEAE undif. 0 5.4 7.3 0 0 0 0 2.1 0 0 0 0 0 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 5.4 0 0 0 0 0 1.6 0.5 4.5 0 0.7 0 0 ASTERACEAE 0 3.2 1.8 1.5 2.8 2.7 0 3.2 0.8 1.8 2.7 0.4 0.3 BRASSICACEAE 0.8 0 0 0.4 0 0 0 0 0 0 0 0 0 Breynia cernua 0 0.5 0 0 0.6 1.6 0 0 0 0 0 0 0 Callitris 1.5 0.5 1.8 0.4 1.1 0.8 0.8 2.1 0 1.8 2.4 2.7 0 Casuarina 0 0 0 0 0 0 0 0 0 0 0 0 0 CHENOPODIACEAE 0 0.5 1.4 0 0 0.4 0 0 0 0 0.3 0 0 Codonocarpus cotinifolius 2.3 0.5 0 0 0 0 0 0.5 1.6 0 0 0.4 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 24.6 1.4 1.8 7 8.8 3.9 0 5.9 8.5 4.1 15.6 3.6 62 CYPERACEAE 1.5 3.2 8.2 0.4 12.2 12.9 2.3 3.2 2.4 1.8 0.7 3.1 1 Dodonaea 0 1.4 0.5 0 1.1 1.6 0.8 1.1 0 1.4 0 0.9 0.3 Elaeocarpus 0 0 0 0 0 0 0 0.5 0 0 0 0 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0 0 0 0 0 0 0 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Ficus 2.3 0.9 0 0.4 0.6 0.4 0 5.3 0.4 2.8 1 0 0 Gomphrena 0 0.5 0 0 0.6 0 0 0.5 0 0 0 0.9 0 Mallotus 0 0 0 0 0 0 0 0 0 0 0.3 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 3.1 2.3 1.8 5.9 2.8 3.1 12.4 5.9 12.1 5 9.5 4 8.9 Myriophyllum 1.5 0 0 0 1.1 0 0 0 0.4 0 0 0.4 0 MYRTACEAE 17.7 14.5 18.3 14.3 11.6 8.6 10.1 14.4 17.8 8.3 9.2 2.2 2.4 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 9.2 13.6 11.4 4.8 17.7 14.8 38 24.1 24.3 20.6 38.1 15.2 6.5 Plantago 0 0.5 1.4 0 0.6 0.4 0 0 0 0.9 0 0 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 26.2 23.1 20.1 63 32.6 37.1 20.9 18.2 25.1 16.5 18.7 10.7 18.5 Podocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 1.1 0 0 0 0 0 Terminalia 3.1 0 0.9 1.8 0.6 0.8 2.3 1.1 1.2 0 0.3 0 0 Timonius timon 0 27.1 22.4 0 4.4 10.5 0 10.2 0.8 34.9 0 54 0 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 0.8 0.5 0.9 0.4 0 0 10.9 0 0 0 0.3 0 0 Typha 0 0.9 0 0 1.1 0.4 0 0 0 0 0 1.3 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 78.2 99.9 167.3 16.5 55.1 22.1 23.5 54.7 11.0 58.5 24.2 80.8 0.0 (particles per cm3 x 100,000) Pollen concentration (grains 10.3 109.7 117.1 104.5 59.0 44.5 11.0 44.8 9.7 79.7 91.5 186.8 0.0 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 3971.0 3207.4 0.0 977.3 3822.1 0.0 2156.7 0.0 365.8 0.0 0.0 0.0 cm3)

240

Depth (cm) 54.1 55.1 56.0 57.1 58.1 59.1 60.1 61.0 62.1 63.1 64.1 65.0 66.1

Acacia 0 0 0 0 0 0 0 0 0 0 0.8 0 0 ACANTHACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 AMARANTHACEAE undif. 0.8 0 0.5 0 0 0 0 0 0 0 0.8 0 0 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 4.4 0.5 4.2 0 1.4 0 2.4 0 2.4 0 1 0 ASTERACEAE 1.2 1.5 5.1 1.7 6.9 0 6.2 12.2 8.5 3.2 7.6 2 5.8 BRASSICACEAE 0 0 0.5 0 0 0 0 0 0 0 0 0 0.6 Breynia cernua 0.4 0 0 0 0 0 2.1 0 1.1 0 0.8 0 0 Callitris 2.5 1.5 0 0 0 2.9 0 2.4 0 3.2 1.7 4.5 0.6 Casuarina 0 0 0 1.7 0 0 0 0 0 4.8 0 1 0 CHENOPODIACEAE 0 0 0 0.8 0 0 0 0 0 1.6 0 0.5 0 Codonocarpus cotinifolius 0.4 0.5 0.5 0.8 0 1.4 0 2.4 0 1.6 0.8 0 0.6 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 7.5 13.2 9.6 4.2 16.6 1.4 16.5 0 7.4 4 19.3 20.8 20.3 CYPERACEAE 0.8 3.4 2.5 7.6 0.7 8.7 1 4.9 1.1 1.6 0 2 0.6 Dodonaea 0.8 1 0 0.8 0 1.4 1 2.4 4.3 0.8 1.7 0 1.2 Elaeocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0.5 0 0 0 0 0 0 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Ficus 2.1 1 0 0 0 0 1 0 0 0 0 2 0 Gomphrena 0 0 0.5 0 0 0 0 0 0 0 0 0 0 Mallotus 0 0 0 0 0 0 0 0 2.1 0 0.8 0 0.6 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 7.9 9.8 1 4.2 1.4 2.9 6.2 2.4 4.3 9.6 2.5 12.4 1.7 Myriophyllum 0 0 0 0 0 0 0 0 0 0 0 0.5 0.6 MYRTACEAE 6.2 10.3 8.6 5 9 10.1 8.2 12.2 11.7 12.8 9.2 17.8 27.3 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 32.8 31.4 34 36.1 35.2 36.2 25.8 39 19.1 16.8 13.4 11.4 9.3 Plantago 0 0 0 0 0 0 0 0 0 0 0 0 0.6 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 19.5 19.6 28.4 31.1 29 31.9 25.8 14.6 39.4 35.2 36.1 20.8 29.7 Podocarpus 0 0 0 0 0.7 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0.5 0 0 0 0 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0.4 2.5 0 1.7 0 1.4 0 0 0 0.8 0 3.5 0 Timonius timon 16.2 0 7.1 0 0.7 0 6.2 0 1.1 0 4.2 0 0.6 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 0.4 0 0 0 0 0 0 4.9 0 1.6 0 0 0 Typha 0 0 0 0 0 0 0 0 0 0 0 0 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 22.9 7.1 35.6 37.5 41.2 26.7 91.7 11.6 74.8 10.8 34.7 24.0 85.4 (particles per cm3 x 100,000) Pollen concentration (grains 63.6 15.5 18.1 16.7 14.4 21.2 7.0 5.6 9.0 44.8 13.5 25.1 14.6 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 99.3 0.0 0.0 0.0 0.0 0.0 113.3 0.0 0.0 cm3)

241

Depth (cm) 67.1 68.8 70.7 72.6 74.5 76.4 78.4 80.3 82.2 84.1 86.0 87.9 89.8

Acacia 0 0 0 1.4 0 0 0 0 0 0 0 0 0 ACANTHACEAE 0 0 0 0 0 0 0.8 0 0 0 0 0 0 AMARANTHACEAE undif. 2 0 0 0 0 0 0 0 0 0 0.4 0 0 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 ASTERACEAE 2.5 1.6 0 0 0 1.2 0.8 1.2 2 0 2.1 3 5.1 BRASSICACEAE 0 0 0 0 0 0 0.8 0 0 0 0 0 0 Breynia cernua 0 0 0 0 0 0 0 0 0 0 0 1.5 0 Callitris 0.5 0 2.7 0 0 0 0 0 0 0 1.7 0 5.1 Casuarina 0.5 0 0 0 7.7 0 0 1.2 0 0 0 0 0 CHENOPODIACEAE 0 0 0 1.4 0 0 0 0 0 0 0 0 0 Codonocarpus cotinifolius 0 0 0 0 0 0 0 1.2 0 0 0 0 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 8.6 12.7 12.2 11.6 0 28.6 17.6 17.3 13.7 25 23.8 18.2 11.9 CYPERACEAE 8.1 3.2 10.8 11.6 15.4 10.7 14.5 12.3 11.8 7.7 5.9 1.5 8.5 Dodonaea 3.5 0.5 2.7 2.9 0 1.2 0 2.5 0 3.8 0 3 0 Elaeocarpus 0 0 0 0 0 1.2 0 2.5 0 0 0.4 0 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0 0 0 0 0 0 0 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Ficus 0 0 0 0 0 0 0.8 0 0 0 0 0 1.7 Gomphrena 0.5 0 1.4 0 0 0 0.8 0 2 1.9 0 3 1.7 Mallotus 0 0 0 0 0 0 0 0 0 0 0 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 14.1 10.1 6.8 1.4 0 1.2 0.8 1.2 2 3.8 1.3 0 3.4 Myriophyllum 0.5 0 1.4 1.4 0 0 0 0 0 0 0.4 0 0 MYRTACEAE 14.1 11.6 8.1 8.7 15.4 6 26 7.4 13.7 26.9 23.8 10.6 5.1 Newcastelia cladotricha 0 0 0 0 0 0 0 1.2 0 0 0 0 0 Pandanus 13.6 18.5 24.3 34.8 23.1 25 22.9 29.6 21.6 7.7 16.3 13.6 18.6 Plantago 0 0.5 1.4 1.4 7.7 0 0 2.5 0 0 0 0 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 27.8 39.7 23 20.3 30.8 22.6 14.5 18.5 31.4 23.1 23.4 45.5 39 Podocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 1.2 0 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0.5 0 0 0 0 0 0 0 0 0 0 0 0 Timonius timon 3 1.6 4.1 1.4 0 0 0 0 2 0 0 0 0 Tribulus 0 0 0 1.4 0 0 0 0 0 0 0 0 0 Trilete fern spore 0 0 0 0 0 0 0 1.2 0 0 0.4 0 0 Typha 0 0 0 0 0 0 0 0 0 0 0 0 0 VERBENACEAE undif. 0 0 1.4 0 0 1.2 0 0 0 0 0 0 0

Charcoal concentration 28.8 42.7 31.3 18.2 232.7 20.2 349.2 44.9 369.0 82.5 112.1 22.8 47.1 (particles per cm3 x 100,000) Pollen concentration (grains 11.4 9.4 7.5 5.0 19.4 10.2 29.1 4.5 106.3 7.3 45.3 6.3 6.4 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 0.0 0.0 0.0 56.0 0.0 0.0 0.0 0.0 0.0 cm3)

242

Depth (cm) 91.7 93.6 95.5 97.5 99.4 101.3 103.2 105.1 107.0 108.9 110.8 112.7 114.6

Acacia 0 0 0.3 0 0 0 0 1.1 0 1.3 1 0.6 0 ACANTHACEAE 0 0.5 0 0 0 0 0 0 0 0 0 1.1 0 AMARANTHACEAE undif. 0 0 0 0 0 0.5 0.6 0 0 0 0 0 0 Amyema 0 0 0 0 0 0.5 0 0 0 0 0 0 0 ARECACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 ASTERACEAE 2.6 1.4 0 0 0.3 1.1 1.1 1.1 1.3 2.1 0 0.6 0.3 BRASSICACEAE 0 0 0.6 0 0.3 2.7 0 0.6 0 0 0 0 0 Breynia cernua 0 0 0 0 0 0 0 0 0 0 0.3 0 0.3 Callitris 0 0 0.3 0 0.3 1.1 0 0.6 0 1.3 0.3 0 0.3 Casuarina 0 0 0 0 0 0.5 0 0 0 0 0 0 0 CHENOPODIACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Codonocarpus cotinifolius 0 0 0.3 0 0 1.1 0 0 0 0.4 0.7 0 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 15.6 5.9 22.4 9.2 23.1 25.3 28.7 26 24.5 27.7 27.5 13.1 25.8 CYPERACEAE 0 12.2 14.7 21 5.4 9.3 2.3 5 0.6 7.7 1.4 14.9 10.9 Dodonaea 2.6 0 1.2 0.8 0.7 1.1 0.6 0 0 0.9 0.7 0.6 0.3 Elaeocarpus 1.3 0 0.9 0 0.7 0 0 0 0 0 0 0 0 ERICACEAE 0 0 0.6 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0 0 0 0.5 0.6 0 0 0 0 0.6 0 EUPHORBIACEAE undif. 0 0 0.9 0.8 0 0 0 0 0 0 0 0 0 Ficus 0 0 0.3 0 0 1.1 0.6 1.1 0 0 0.3 1.1 0.3 Gomphrena 2.6 0.9 0 1.7 0.7 1.1 0 0 0.6 3 0.7 0 0.3 Mallotus 0 0 8.2 0 0.7 0 1.1 0 0 0 0.3 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 1.3 1.8 3.5 4.2 3.1 2.7 9.2 1.7 0 2.1 0.7 0.6 0.9 Myriophyllum 0 0 0 0 0 0 0 0 0 0 0 0 0 MYRTACEAE 40.3 33.8 8.8 11.8 23.5 15.9 10.9 28.7 11.3 20 32.4 31.4 28.6 Newcastelia cladotricha 0 0 0 0 0 0 0 0.6 0 0 0 0 0 Pandanus 7.8 20.3 13.5 10.9 9.2 10.4 18.4 11 35.8 2.6 1.4 2.9 3.7 Plantago 0 0 0.3 0 0 1.1 0 0 0 0.9 0 0 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0.6 0 0 0 0 POACEAE 23.4 23.4 22.4 39.5 31.3 23.6 25.3 22.1 24.5 28.9 31.7 28.6 27.6 Podocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 0 0 0.6 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0 0 0.3 0 0.3 0 0 0 0 0.9 0.3 0 0.6 Timonius timon 0 0 0 0 0 0 0.6 0 0 0 0 0 0 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 2.6 0 0.6 0 0.3 0 0 0.6 0 0.4 0 4 0 Typha 0 0 0 0 0 0 0 0 0 0 0 0 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 70.4 236.5 98.8 68.5 90.1 27.9 42.9 45.9 49.1 21.8 131.3 134.0 136.5 (particles per cm3 x 100,000) Pollen concentration (grains 11.1 33.3 31.0 11.1 58.9 13.3 10.2 8.5 9.7 10.0 75.7 61.8 93.2 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 0.0 73.2 0.0 0.0 0.0 0.0 0.0 0.0 289.6 cm3)

243

Depth (cm) 116.6 118.5 120.4 122.3 124.2 126.1 128.0 129.9 131.8 133.7 135.7 137.6 139.5

Acacia 0.4 0 0.7 0 0 0 0 0 0.4 0.4 0.4 0 0 ACANTHACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 AMARANTHACEAE undif. 0.4 0.3 0 0 0 0 0 0 0 0 0 0 0.5 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 ASTERACEAE 2.4 0.3 0.7 0 0 0.4 0.4 0.4 0 0.4 0.8 0 0.5 BRASSICACEAE 0 0.3 0 1 1.4 0 0 0 0 0 0 0 0 Breynia cernua 0.4 0 0.7 0 0 0 0.4 0 0 0 0 0.4 0 Callitris 0.8 0.6 0.4 0.3 2.3 0 0.7 0.4 0.4 0 0.4 0.4 0.5 Casuarina 0 0 0 0 0 0 0 0 0 0 0.4 0 0 CHENOPODIACEAE 0 0 0 0 0 0 1.1 0 1.1 0 0 0.8 0.5 Codonocarpus cotinifolius 0 0.6 0.4 0.3 0 0 0 0 0 0 0 0 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 14.6 25.9 13.1 23.6 17.1 17.1 15.7 18.1 10.7 23.5 10.1 20.5 9.1 CYPERACEAE 4.7 10.8 10.9 9.5 6.9 1.6 10.6 0.8 14 2.6 6 1.5 8.7 Dodonaea 1.2 0 0.4 0.3 0 0.4 0 0 0.4 0 0 0.4 0 Elaeocarpus 0.4 0 0.4 0 0 0 0 0 0.4 0 0 0 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0 0 0 0 0 0 0 0 0 0 0 0.4 0 EUPHORBIACEAE undif. 0 0.3 0 0 0 0 0 0 0 0 0 0 0.9 Ficus 0 0.3 0.7 0.3 0 0 0 0 0.4 0 0.4 0 0.9 Gomphrena 3.6 0.6 1.5 1.3 0.9 2 2.2 2 1.1 2.2 1.2 0.8 1.4 Mallotus 0 0 0 0 0 0 0 0 0 0 0.4 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Monolete fern spore 1.2 0.3 0.7 0.3 3.7 0 1.1 0.8 1.5 0.4 0.8 0.4 0.5 Myriophyllum 0 0 0.4 0 0 0 0 0 0 0 0 0.4 0 MYRTACEAE 20.9 30.1 29.6 30.8 33.3 40.9 36.5 39.8 44.5 36.4 46.4 45.2 31.1 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 12.6 4.5 20.6 4.9 14.4 2 4.7 5.2 4 1.1 4.8 1.9 12.8 Plantago 0.8 0.6 0 0 0.5 0.4 0 0 0 0.7 0.8 0 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 34.4 24.1 18.7 26.9 19.4 34.9 26.6 32.5 20.6 32.4 26.6 26.6 32.9 Podocarpus 0 0 0 0 0 0 0 0 0 0 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0.4 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0.8 0 0 0 0 0.4 0 0 0 0 0 0 0 Timonius timon 0 0 0 0 0 0 0 0 0 0 0 0 0 Tribulus 0 0 0 0.3 0 0 0 0 0 0 0 0 0 Trilete fern spore 0.4 0.3 0 0 0 0 0 0 0.7 0 0 0 0 Typha 0 0 0 0 0 0 0 0 0 0 0.4 0 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 64.4 91.4 114.9 776.8 153.9 409.5 74.2 95.8 151.9 74.1 76.7 90.3 64.0 (particles per cm3 x 100,000) Pollen concentration (grains 21.4 94.8 45.3 54.8 104.7 54.2 31.9 60.4 270.0 78.8 40.4 64.3 13.8 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 62.8 cm3)

244

Depth (cm) 141.4 143.3 145.2 147.1 149.0 150.9 152.8 154.8 156.7 158.6 160.5 162.4 232.0

Acacia 0 0 0.4 0 0 0.3 0.8 0 0.4 0.5 0 0 0 ACANTHACEAE 0 0.4 0 0 0 0 0 0 0 0.9 0 0 0 AMARANTHACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Amyema 0 0 0 0 0 0 0 0 0 0 0 0 0 ARECACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 ASTERACEAE 0 0.7 1.9 0 0.5 0.3 0 0 0 0 0 0.7 1.1 BRASSICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Breynia cernua 0 0.4 0 0 0 0 0 0 0 0 0 0 0 Callitris 0 0.7 0.8 0 0.3 1.1 0 0 0 0.9 0 0 0 Casuarina 0 0 0 0 0 0 0 0.6 0 0 0 0 0 CHENOPODIACEAE 0 0.4 0 0 0 0 0 0 0 0.5 0 0 0 Codonocarpus cotinifolius 0 0 0 0 0 0.8 0 0 0 0.5 0 0 0 Colocasia esculenta 0 0 0 0 0 0 0 0 0 0 0 0 0 Cycnogeton dubium 12.2 12.5 14.7 14.9 18.6 14 12.4 12.2 9 4.2 10.2 5.8 2.2 CYPERACEAE 5.5 13.2 7.7 9.3 2.8 12.6 3.7 17.3 3.4 0.9 2.8 1.4 1.1 Dodonaea 0 0 0 0.6 0.5 0.3 0 0 0 0 0.6 0.7 0 Elaeocarpus 0 0 0 0 0 0.5 0 0.6 0 0 0 0 0 ERICACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Euphorbia 0.4 0 0 0 0.3 0 0 0 0.4 0 0 0 0 EUPHORBIACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 Ficus 0 0 0.4 0.6 0 0.8 0 1.3 0.4 0.5 0 0.7 0 Gomphrena 0 1.1 0.8 1.2 0 0 3.7 1.9 0 0.5 0.6 3.6 2.2 Mallotus 0 0 0 0 0 0 0 0 0 0 0 0 0 MALVACEAE 0 0 0 0 0 0 0 0 0 0.5 0 0 0 Monolete fern spore 0.4 1.1 0.4 1.9 1.5 0.3 0.8 0.6 0 1.9 0.6 1.4 5.4 Myriophyllum 0 0 0 0 0 0 0 0 0 0 0 0 0 MYRTACEAE 59.8 48.7 35.9 21.7 31.4 35.1 48.1 24.4 58.5 36.6 38.4 51.1 41.3 Newcastelia cladotricha 0 0 0 0 0 0 0 0 0 0 0 0 0 Pandanus 2.4 9.2 8.5 10.6 23.1 20.8 4.6 2.6 2.1 1.4 1.1 0 0 Plantago 0 0 0.8 0 0 0 0.4 0 0 0.9 0 0 0 Plectranthus congestus 0 0 0 0 0 0 0 0 0 0 0 0 0 POACEAE 19.3 11.7 27.4 38.5 21.1 11.8 25.3 37.8 25.6 48.6 45.8 34.5 46.7 Podocarpus 0 0 0 0 0 0 0 0 0 0.5 0 0 0 PROTEACEAE 0 0 0 0 0 0 0 0 0 0.5 0 0 0 SAPINDACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0 SAPOTACEAE 0 0 0 0 0 0 0 0 0 0 0 0 0 Terminalia 0 0 0 0.6 0 0.5 0 0 0 0 0 0 0 Timonius timon 0 0 0.4 0 0 0 0 0 0 0 0 0 0 Tribulus 0 0 0 0 0 0 0 0 0 0 0 0 0 Trilete fern spore 0 0 0 0 0 0.8 0 0.6 0 0 0 0 0 Typha 0 0 0 0 0 0 0 0 0 0 0 0 0 VERBENACEAE undif. 0 0 0 0 0 0 0 0 0 0 0 0 0

Charcoal concentration 71.7 11.8 78.6 46.3 80.1 19.4 91.1 69.6 14.1 6.6 9.7 16.1 14.3 (particles per cm3 x 100,000) Pollen concentration (grains 91.3 33.3 43.5 12.5 79.0 152.2 31.2 8.1 15.3 3.6 6.2 4.2 3.5 per cm3 x 1000) Pseudoschizaea concentration (structures per 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 cm3)

245

BSP02

Depth (cm) 4 10 20 30 40 50 60 70 80 90

Acacia 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 AMARANTHACEAE undif. 0.0 0.9 0.0 2.8 0.8 0.6 2.1 0.7 1.3 1.7 ASTERACEAE 0.0 0.9 0.8 0.0 0.0 0.6 0.7 0.0 2.0 1.7 Atalaya hemiglauca 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Banksia dentata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Breynia cernua 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Codonocarpus cotinifolius 0.0 0.0 0.8 1.4 0.0 0.6 0.0 0.0 0.0 0.0 Colocasia esculenta 0.0 1.7 1.5 0.0 0.8 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 4.5 6.8 11.4 9.2 4.8 5.5 18.4 6.3 7.0 1.3 CYPERACEAE 1.5 1.7 7.6 9.9 11.3 3.7 10.6 2.8 1.7 0.3 Decaisnina signata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Dodonaea 3.0 0.9 1.5 0.0 1.6 0.6 0.0 0.7 0.3 0.3 Eucalyptus 13.6 5.1 3.8 7.7 4.0 9.1 9.9 13.2 8.3 2.3 Euphorbia sp 0.0 0.9 0.0 0.0 0.0 0.6 0.7 0.7 1.0 0.0 EUPHORBIACEAE 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 Fabaceae 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Gomphrena 0.0 0.0 0.0 1.4 0.0 0.0 0.0 0.0 0.3 0.0 Grevillea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Mallotus 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 Melaleuca 6.1 3.4 6.8 6.3 8.1 5.5 22.7 7.6 13.6 5.7 Melastoma affine 0.0 0.0 0.8 0.0 0.0 0.6 0.0 0.0 1.0 0.0 Monolete fern spore 0.0 2.6 5.3 4.9 1.6 2.4 4.3 5.6 5.3 4.3 Myriophyllum 0.0 0.0 1.5 0.7 0.0 0.0 0.0 0.7 0.0 0.0 Ocimum basilicum/Basilicum 0.0 0.0 0.8 0.0 0.8 1.2 0.0 0.0 0.3 0.0 polystachyon Pandanus 18.2 21.4 29.5 28.9 19.4 26.2 14.9 29.9 22.2 45.3 Picea 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plectranthus congestus 0.0 0.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 0.0 POACEAE 16.7 13.7 22.7 19.7 21.0 37.8 12.8 29.2 20.2 16.0 Pouteria sericea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SAPOTACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 Timonius timon 36.4 39.3 4.5 4.9 23.4 1.8 0.7 2.8 14.2 21.0 Trilete fern spore 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Typha 0.0 0.0 0.0 0.7 0.0 0.0 0.7 0.0 0.0 0.0 Ventilago viminalis 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 VERBENACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 Wrightia 0.0 0.0 0.0 0.0 0.8 0.6 0.0 0.0 0.3 0.0 Charcoal accumulation rate (grains 14.9 31.2 24.9 152.9 20.2 30.4 65.9 18.9 43.8 11.8 per sample per year x 10,000) Pollen accumulation rate (grains per 1.9 6.0 4.9 6.7 7.1 5.1 4.6 4.8 10.0 12.6 sample per year x 100) Entorrhiza accumulation rate (grains 26.2 102.4 110.5 642.2 314.7 532.8 212.2 30.2 0.0 0.0 per sample per year) Glomus accumulation rate (grains per 67.0 76.8 62.6 94.4 114.4 49.6 9.8 100.6 3.3 0.0 sample per year) Pseudoschizaea accumulation rate 5.8 10.2 70.0 89.7 57.2 49.6 19.6 23.5 13.2 0.0 (grains per sample per year) Tilletia accumulation rate (grains per 5.8 56.3 84.7 184.2 85.8 34.1 3.3 6.7 0.0 0.0 sample per year)

246

Depth (cm) 100 110 120 130 140 150 160 170 180 190

Acacia 0.0 0.3 0.3 0.3 0.0 0.0 0.4 0.7 0.0 0.3 Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 AMARANTHACEAE undif. 0.3 1.3 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 ASTERACEAE 6.6 7.7 2.3 0.3 1.5 0.0 2.6 1.3 1.0 0.3 Atalaya hemiglauca 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Banksia dentata 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 Breynia cernua 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Codonocarpus cotinifolius 0.3 0.0 0.0 0.0 0.0 0.0 0.4 0.7 0.3 0.0 Colocasia esculenta 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Cycnogeton dubium 14.4 10.3 14.3 14.6 18.5 17.2 37.2 36.2 18.3 21.3 CYPERACEAE 3.3 1.7 1.7 4.5 0.0 0.9 0.7 4.3 8.6 4.3 Decaisnina signata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 Dodonaea 1.3 0.3 1.7 0.3 0.0 0.0 0.0 0.3 0.7 0.7 Eucalyptus 5.2 4.3 4.7 7.8 6.2 4.3 8.9 10.6 21.3 20.0 Euphorbia sp 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.7 0.0 EUPHORBIACEAE 0.0 0.0 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 Fabaceae 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.7 0.7 0.0 Gomphrena 0.3 1.3 0.0 0.0 0.0 0.9 0.4 0.7 2.3 1.3 Grevillea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Mallotus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Melaleuca 7.5 9.7 16.3 6.6 6.2 6.9 3.7 5.3 9.6 10.7 Melastoma affine 1.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.3 0.0 Monolete fern spore 2.0 5.7 1.0 1.8 1.5 3.4 1.1 1.0 0.0 0.7 Myriophyllum 0.0 0.7 0.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 Ocimum basilicum/Basilicum 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 polystachyon Pandanus 35.7 21.0 35.7 48.4 46.2 37.1 6.3 1.7 0.7 1.7 Picea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 Plectranthus congestus 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 POACEAE 18.4 31.3 21.3 14.9 16.9 19.8 37.5 34.9 33.6 38.3 Pouteria sericea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 SAPOTACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Timonius timon 2.6 2.7 0.3 0.0 1.5 6.0 0.0 0.0 0.0 0.0 Trilete fern spore 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.3 Typha 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Ventilago viminalis 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 VERBENACEAE 0.0 0.3 0.0 0.0 0.0 0.9 0.4 0.0 0.0 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Wrightia 0.7 0.0 0.0 0.0 1.5 0.0 0.0 0.0 0.0 0.0 Charcoal accumulation rate (grains 13.6 76.1 5.3 34.3 42.5 38.9 5.0 6.8 11.7 29.6 per sample per year x 10,000) Pollen accumulation rate (grains per 6.8 3.9 6.1 4.9 3.5 3.1 5.5 6.0 5.5 4.3 sample per year x 100) Entorrhiza accumulation rate (grains 24.7 20.8 12.3 10.4 10.9 16.2 0.0 0.0 0.0 0.0 per sample per year) Glomus accumulation rate (grains per 6.7 0.0 6.1 0.0 16.4 0.0 0.0 2.0 0.0 0.0 sample per year) Pseudoschizaea accumulation rate 4.5 2.6 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (grains per sample per year) Tilletia accumulation rate (grains per 11.2 2.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 sample per year)

247

Depth (cm) 200 210 220 230 240

Acacia 0.0 0.3 0.0 0.0 0.0 Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 0.0 AMARANTHACEAE undif. 0.0 0.0 0.0 0.0 0.0 ASTERACEAE 0.0 0.7 0.0 0.9 0.0 Atalaya hemiglauca 0.0 0.0 0.0 0.0 0.0 Banksia dentata 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 0.0 Breynia cernua 0.3 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.0 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.0 0.0 0.0 Colocasia esculenta 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 19.7 6.7 12.9 13.6 4.3 CYPERACEAE 4.6 2.0 3.6 2.7 0.0 Decaisnina signata 0.0 0.0 0.0 0.0 0.0 Dodonaea 0.3 0.0 0.0 0.0 0.0 Eucalyptus 15.1 29.7 13.7 24.5 17.4 Euphorbia sp 0.0 0.0 0.0 0.0 0.0 EUPHORBIACEAE 0.0 0.0 0.0 0.0 0.0 Fabaceae 0.0 0.0 0.0 0.0 0.0 Gomphrena 0.7 1.3 1.4 1.8 0.0 Grevillea 0.0 0.0 0.0 0.0 0.0 Mallotus 0.0 0.0 0.0 0.0 0.0 Melaleuca 16.4 12.7 1.4 3.6 0.0 Melastoma affine 0.0 0.0 0.0 0.0 0.0 Monolete fern spore 0.0 0.0 0.0 0.0 0.0 Myriophyllum 0.0 0.0 0.0 0.0 0.0 Ocimum basilicum/Basilicum 0.0 0.0 0.0 0.0 0.0 polystachyon Pandanus 0.7 0.3 0.0 0.0 0.0 Picea 0.0 0.0 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 0.0 Plectranthus congestus 0.0 0.0 0.0 0.0 0.0 POACEAE 41.3 46.3 66.9 52.7 78.3 Pouteria sericea 0.0 0.0 0.0 0.0 0.0 SAPOTACEAE 0.0 0.0 0.0 0.0 0.0 Timonius timon 0.3 0.0 0.0 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 0.0 Typha 0.7 0.0 0.0 0.0 0.0 Ventilago viminalis 0.0 0.0 0.0 0.0 0.0 VERBENACEAE 0.0 0.0 0.0 0.0 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 Wrightia 0.0 0.0 0.0 0.0 0.0 Charcoal accumulation rate (grains 4.6 6.6 3.2 7.9 12.7 per sample per year x 10,000) Pollen accumulation rate (grains per 2.8 2.1 0.4 1.1 0.7 sample per year x 100) Entorrhiza accumulation rate (grains 1.8 0.0 0.0 0.0 0.0 per sample per year) Glomus accumulation rate (grains per 0.0 1.4 0.3 0.0 0.0 sample per year) Pseudoschizaea accumulation rate 0.0 0.0 0.0 0.0 0.0 (grains per sample per year) Tilletia accumulation rate (grains per 0.0 0.0 0.0 0.0 0.0 sample per year)

248

ELZ01

Depth (cm) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.5 51.5

Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 AMARANTHACEAE 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Amyema 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ASTERACEAE 0.3 0.3 0.1 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Banksia dentata 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 Breynia cernua 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Buchanania obovata 2.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Casuarina 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 Clerodendrum floribundum 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 Colocasia esculenta 3.3 0.7 0.1 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 2.7 5.3 1.2 3.0 0.7 2.3 1.6 0.3 0.2 0.0 1.3 CYPERACEAE 0.0 0.0 3.0 1.3 0.3 0.0 1.0 1.6 4.6 1.2 1.3 Dodonaea 0.0 0.7 0.2 0.7 0.0 0.0 0.0 0.3 0.3 0.0 0.0 Elaeocarpus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Eucalyptus 6.0 7.3 4.2 5.7 11.1 12.3 12.9 19.7 12.2 18.3 12.3 Euphorbia 0.0 0.0 0.1 0.0 0.7 0.0 1.0 0.0 0.2 0.0 0.3 EUPHORBIACEAE 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 FABACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 Ficus 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 Gomphrena 0.0 0.3 1.5 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 Grevillea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 Hypericum gramineum 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 Melaleuca 9.7 3.3 3.7 4.0 8.8 6.3 9.6 17.1 13.2 6.1 21.3 Melastoma affine 1.0 1.3 0.4 0.7 0.3 0.3 1.3 1.0 0.4 0.0 0.0 Monolete fern spore 0.0 0.0 0.3 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 Myriophyllum 28.0 17.7 17.9 23.0 15.7 20.0 13.2 4.9 4.6 0.0 7.0 MYRTACEAE 0.0 0.0 0.0 0.0 0.3 0.0 0.0 1.0 0.0 0.0 0.3 Ocimum basilicum/Basilicum 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 polystachyon Opilia amentacea 0.0 0.0 0.0 0.0 0.0 1.0 0.6 0.0 0.0 0.0 0.7 Pandanus 0.7 1.7 0.8 0.0 0.3 0.7 1.9 1.3 0.8 1.2 1.0 Picea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 Plectranthus congestus 0.0 0.0 0.1 0.3 0.0 0.0 0.3 0.3 0.0 0.0 0.0 POACEAE 45.0 59.7 64.9 60.7 56.5 42.7 53.1 47.7 62.8 70.7 53.8 Podocarpus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 PROTEACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SAPINDACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 Trilete fern spore 0.0 0.0 0.6 0.0 0.0 0.0 0.3 0.0 0.1 0.0 0.0 Typha 0.7 1.7 0.3 0.0 4.9 12.7 2.3 3.9 0.0 2.4 0.3 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Wrightia 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 Charcoal accumulation rate (particles 1.8 9.5 7.7 7.3 5.2 0.7 1.3 6.5 1.0 0.1 1.0 per cm per year x 10,000) Pollen accumulation rate (grains per 3.0 19.9 7.5 5.8 2.8 1.4 2.2 15.5 3.6 0.1 4.1 cm per year x 100) Entorrhiza accumulation rate 1.0 79.3 0.0 30.8 0.9 0.5 0.0 0.0 0.0 0.0 0.0 (structures per sample per year) Glomus accumulation rate (structures 17.0 542.1 4.4 26.9 4.5 0.5 0.0 20.4 0.6 0.0 1.4 per sample per year) Pseudoschizaea accumulation rate 2.0 0.0 2.9 3.8 8.2 6.8 0.0 0.0 1.2 0.0 2.7 (structures per sample per year) Tilletia accumulation rate (structures 0.0 39.7 1.5 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 per sample per year) 249

Depth (cm) 56.5 61.5 66.5 71.5 76.5 81.5 86.5 91.5 97.0 101.5 106.5

Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 AMARANTHACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Amyema 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.0 0.0 0.0 0.0 ASTERACEAE 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Banksia dentata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Breynia cernua 0.0 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Buchanania obovata 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.7 0.0 Callitris 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Casuarina 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Clerodendrum floribundum 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Colocasia esculenta 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 0.7 0.7 0.3 1.0 0.0 0.7 0.8 0.0 0.3 0.3 0.3 CYPERACEAE 1.3 0.7 1.0 2.7 0.7 0.7 0.0 0.3 0.7 0.7 1.0 Dodonaea 0.0 0.7 0.3 0.0 0.0 0.7 0.4 0.0 0.0 1.0 0.0 Elaeocarpus 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Eucalyptus 23.0 21.1 24.1 33.4 59.3 25.2 32.7 35.8 22.8 18.7 20.7 Euphorbia 0.0 0.7 0.3 0.3 0.3 0.3 0.0 0.7 0.0 0.0 0.7 EUPHORBIACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 FABACEAE 0.0 0.7 1.0 0.3 0.0 0.7 0.0 0.0 0.7 2.7 1.3 Ficus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Gomphrena 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Grevillea 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Hypericum gramineum 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Melaleuca 7.7 12.5 11.9 17.4 15.3 19.0 12.7 26.2 17.5 16.7 20.3 Melastoma affine 0.3 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Monolete fern spore 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Myriophyllum 1.7 2.0 2.0 2.0 0.7 0.7 1.6 0.3 1.7 2.7 3.0 MYRTACEAE 0.0 0.0 1.0 0.0 0.0 1.3 0.8 0.3 0.7 0.0 0.0 Ocimum basilicum/Basilicum 0.0 0.0 0.7 0.0 0.0 0.3 0.4 0.0 0.0 0.0 0.3 polystachyon Opilia amentacea 0.0 0.3 0.0 0.0 0.0 0.3 1.2 1.0 0.7 0.0 0.0 Pandanus 4.0 2.3 3.3 5.0 0.3 8.5 7.8 2.0 6.6 6.3 5.3 Picea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plectranthus congestus 0.3 0.0 0.3 0.0 0.0 0.0 0.4 0.0 0.3 0.0 0.0 POACEAE 56.7 55.1 50.5 36.8 22.7 35.3 33.9 31.8 47.4 41.7 45.7 Podocarpus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 PROTEACEAE 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 SAPINDACEAE 0.0 0.3 0.0 0.3 0.0 0.3 0.0 0.0 0.0 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Typha 4.0 1.7 3.0 0.0 0.0 5.6 6.9 1.7 0.7 7.7 1.3 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Wrightia 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Charcoal accumulation rate (particles 8.2 2.9 2.6 1.6 0.0 0.7 0.1 5.1 6.7 0.9 1.6 per cm per year x 10,000) Pollen accumulation rate (grains per 9.4 3.2 6.7 1.9 2.3 1.2 0.9 8.4 7.0 2.0 4.2 cm per year x 100) Entorrhiza accumulation rate 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (structures per sample per year) Glomus accumulation rate (structures 6.3 0.0 2.2 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 per sample per year) Pseudoschizaea accumulation rate 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 0.0 (structures per sample per year) Tilletia accumulation rate (structures 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 per sample per year)

250

Depth (cm) 111.5 116.5 121.5 126.5

Adriana glabrata var. acerifolia 0.0 0.0 0.0 0.0 AMARANTHACEAE 0.0 0.0 0.0 0.0 Amyema 0.0 0.0 0.0 0.0 ASTERACEAE 0.3 0.0 0.0 1.9 Banksia dentata 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 Breynia cernua 0.0 0.0 1.6 0.0 Buchanania obovata 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.0 0.0 Casuarina 0.0 0.0 0.0 0.0 Clerodendrum floribundum 0.0 0.0 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.0 0.0 Colocasia esculenta 0.0 0.0 0.0 0.0 Cycnogeton dubium 0.3 1.0 1.6 1.9 CYPERACEAE 0.3 0.0 0.0 0.0 Dodonaea 0.0 0.0 0.0 1.9 Elaeocarpus 0.0 0.0 0.0 0.0 Eucalyptus 22.8 36.2 26.2 18.5 Euphorbia 0.3 0.0 0.0 0.0 EUPHORBIACEAE 0.0 0.0 0.0 0.0 FABACEAE 1.6 2.3 4.9 0.0 Ficus 0.0 0.0 0.0 0.0 Gomphrena 0.0 0.0 0.0 0.0 Grevillea 0.0 0.0 0.0 0.0 Hypericum gramineum 0.0 0.0 0.0 0.0 Melaleuca 28.3 17.3 27.9 1.9 Melastoma affine 0.3 0.0 0.0 0.0 Monolete fern spore 0.0 0.0 1.6 1.9 Myriophyllum 1.9 2.3 3.3 5.6 MYRTACEAE 1.6 0.3 0.0 1.9 Ocimum basilicum/Basilicum 0.0 0.0 0.0 0.0 polystachyon Opilia amentacea 3.2 1.0 0.0 0.0 Pandanus 13.2 14.6 9.8 7.4 Picea 0.3 0.0 0.0 0.0 Plantago 0.0 0.0 0.0 0.0 Plectranthus congestus 0.0 0.0 0.0 0.0 POACEAE 20.9 21.3 23.0 57.4 Podocarpus 0.0 0.0 0.0 0.0 PROTEACEAE 0.0 0.0 0.0 0.0 SAPINDACEAE 0.0 0.0 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 Typha 4.5 3.7 0.0 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 Wrightia 0.0 0.0 0.0 0.0 Charcoal accumulation rate (particles 0.2 0.0 24.8 0.1 per cm per year x 10,000) Pollen accumulation rate (grains per 0.7 0.2 0.1 0.0 cm per year x 100) Entorrhiza accumulation rate 0.0 0.0 0.0 0.0 (structures per sample per year) Glomus accumulation rate (structures 0.0 0.1 0.2 0.3 per sample per year) Pseudoschizaea accumulation rate 0.0 0.0 0.0 0.0 (structures per sample per year) Tilletia accumulation rate (structures 0.0 0.0 0.0 0.0 per sample per year)

251

FRN02

Depth (cm) 0.5 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0

Acacia 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Aidia racemosa 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 AMARANTHACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Amyema 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ASTERACEAE 0.3 3.5 0.6 0.0 1.2 0.0 0.0 0.0 0.7 0.0 0.0 Banksia dentata 0.0 0.0 0.0 1.2 0.0 0.3 0.0 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 Breynia cernua 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Callitris 0.0 0.0 0.0 0.0 0.0 0.3 0.4 0.0 0.7 0.0 0.0 Casuarina 0.0 0.9 0.0 0.0 0.0 0.3 0.0 0.0 0.3 0.0 0.0 Celtis philippinensis 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 Codonocarpus cotinifolius 0.0 1.8 0.0 0.0 0.0 0.0 0.0 0.7 0.7 0.0 0.0 Colocasia esculenta 0.0 2.6 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 4.7 0.0 0.0 0.0 0.0 1.0 0.8 0.0 2.3 0.3 0.0 CYPERACEAE 11.0 8.8 0.0 0.0 4.9 6.7 4.6 5.3 5.0 4.0 1.2 Dodonaea 1.0 0.9 0.0 0.0 0.0 0.3 0.0 0.3 1.7 1.3 0.0 Drosera 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Eremophila 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.3 0.3 0.0 ERICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 Eucalyptus 6.3 23.7 38.6 14.8 23.2 27.7 10.9 5.7 6.7 23.7 46.2 Euphorbia 0.7 0.0 0.0 2.5 0.0 0.0 0.4 0.3 1.0 0.0 0.3 Gomphrena 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Grevillea 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.3 0.0 0.0 0.3 Mallotus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.3 0.0 Melaleuca 20.3 26.3 13.3 7.4 19.5 12.3 6.3 1.3 8.7 13.3 32.4 Melastoma affine 0.3 0.0 0.0 0.0 0.0 0.0 0.8 0.7 3.3 0.3 0.0 Monolete fern spore 0.7 1.8 1.3 7.4 2.4 10.3 13.0 2.7 22.3 9.3 0.6 Myriophyllum 2.3 2.6 4.4 0.0 4.9 1.3 5.9 4.3 1.7 4.7 1.5 Ocimum basilicum/Basilicum 20.7 0.9 0.0 0.0 8.5 1.0 0.8 1.3 0.7 1.0 0.3 polystachyon Opilia amentacea 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Pandanus 14.0 12.3 1.3 11.1 11.0 2.0 0.0 5.3 3.7 3.7 0.6 Plantago 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Plectranthus congestus 0.7 0.0 0.6 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 POACEAE 16.3 12.3 36.7 55.6 20.7 35.0 54.2 70.0 38.7 36.7 15.0 PROTEACEAE 0.0 0.0 0.0 0.0 0.0 0.3 0.8 0.0 0.0 0.0 0.0 SAPINDACEAE 0.0 1.8 0.6 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 Timonius timon 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.3 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.3 0.0 0.0 Typha 0.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 0.0 0.3 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 1.2 0.0 0.0 0.0 0.0 0.0 1.5 Wrightia 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Charcoal accumulation rate (particles 26.5 8.1 34.0 24.5 4.3 14.9 9.5 14.0 33.0 16.9 2.0 per sample per year x 10,000) Pollen accumulation rate (grains per 15.0 2.0 3.5 3.2 1.3 7.5 1.6 2.7 5.7 6.9 4.7 sample per year x 100) Entorrhiza accumulation rate (grains per 209.3 52.0 15.6 27.4 480.0 5.0 8.0 163.0 0.0 18.2 0.0 sample per year) Glomus accumulation rate (grains per 348.9 263.4 172.1 66.6 307.1 12.4 12.0 1.8 0.0 0.0 0.0 sample per year) Pseudoschizaea accumulation rate 39.9 9.0 20.1 27.4 3.1 44.7 30.6 89.5 16.9 29.6 16.0 (grains per sample per year) Tilletia accumulation rate (grains per 64.8 3.6 31.3 0.0 1.5 0.0 0.0 0.0 0.0 0.0 21.3 sample per year)

252

Depth (cm) 110.0 120.0 130.0 140.0 150.0 160.0 170.0 180.5 190.5 199.5

Acacia 0.0 0.0 0.0 0.0 1.2 1.2 0.0 0.3 0.0 0.0 Aidia racemosa 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 AMARANTHACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Amyema 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 ASTERACEAE 0.0 0.2 0.6 0.0 0.0 0.0 0.0 0.0 0.3 1.4 Banksia dentata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 BRASSICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.4 Breynia cernua 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Callitris 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Casuarina 0.0 0.0 0.0 0.6 1.2 0.0 0.0 0.0 0.0 0.0 Celtis philippinensis 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.3 0.0 0.0 Colocasia esculenta 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Cycnogeton dubium 0.8 1.2 1.1 1.7 2.4 0.0 2.1 2.7 2.3 2.9 CYPERACEAE 4.8 2.8 1.1 14.7 4.9 0.0 2.1 1.0 0.7 4.3 Dodonaea 0.3 0.2 1.1 0.6 1.2 2.4 0.0 0.0 1.0 0.0 Drosera 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Eremophila 0.0 0.0 0.0 0.0 1.2 0.0 0.0 0.0 0.0 0.0 ERICACEAE 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Eucalyptus 17.9 7.2 30.5 12.4 18.3 42.7 25.0 44.3 28.9 40.6 Euphorbia 0.3 0.2 0.6 0.6 0.0 0.0 0.0 0.3 0.3 0.0 Gomphrena 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Grevillea 0.0 0.2 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 Mallotus 0.0 0.3 0.6 4.5 0.0 0.0 2.1 0.0 0.0 0.0 Melaleuca 13.3 11.0 18.4 15.8 31.7 13.4 10.4 7.3 4.6 1.4 Melastoma affine 0.3 0.0 0.6 0.6 0.0 0.0 0.0 0.3 0.3 0.0 Monolete fern spore 2.9 14.8 7.5 7.9 7.3 1.2 8.3 7.0 4.3 7.2 Myriophyllum 10.9 3.1 13.2 5.6 4.9 6.1 8.3 1.7 2.0 0.0 Ocimum basilicum/Basilicum 0.0 0.5 0.0 0.0 0.0 0.0 0.0 1.0 0.3 0.0 polystachyon Opilia amentacea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Pandanus 8.3 2.9 4.6 4.5 6.1 1.2 4.2 3.7 5.6 10.1 Plantago 0.3 0.5 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 Plectranthus congestus 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 POACEAE 39.5 54.1 19.0 28.8 17.1 22.0 35.4 21.0 23.0 29.0 PROTEACEAE 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.4 SAPINDACEAE 0.0 0.0 0.0 0.0 0.0 3.7 2.1 0.0 0.0 0.0 Timonius timon 0.0 0.0 0.6 0.6 2.4 0.0 0.0 0.3 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 0.0 3.7 0.0 0.0 0.0 0.0 Typha 0.0 0.0 0.0 0.0 0.0 2.4 0.0 8.7 25.7 0.0 Vigna lanceolata 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Wrightia 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Charcoal accumulation rate (particles 3.2 6.0 0.9 0.4 0.2 0.6 0.1 5.2 5.3 0.6 per sample per year x 10,000) Pollen accumulation rate (grains per 3.1 9.1 0.6 0.2 0.2 0.2 0.1 1.7 1.1 0.5 sample per year x 100) Entorrhiza accumulation rate (grains per 0.0 0.0 0.6 0.5 0.0 0.0 0.1 1.2 1.4 1.8 sample per year) Glomus accumulation rate (grains per 0.8 1.5 1.6 1.6 0.5 0.5 0.8 0.6 0.0 2.8 sample per year) Pseudoschizaea accumulation rate 1.6 4.6 1.9 0.1 0.0 0.0 0.0 7.1 3.3 0.0 (grains per sample per year) Tilletia accumulation rate (grains per 0.8 12.3 3.2 0.3 0.2 0.0 0.4 1.2 0.4 1.4 sample per year)

253

Surface samples D4, MP0, MP1, MP2 and MP3

Sample ID D4 MP0 MP2 MP1 MP3

Acacia 0.0 0.4 0.2 0.0 0.0 AMARANTHACEAE undif. 13.8 0.8 0.5 9.8 0.0 ARECACEAE 2.5 0.8 4.2 9.0 0.0 ASTERACEAE 1.9 0.0 0.7 0.0 1.3 Banksia dentata 0.6 0.0 0.0 0.0 0.0 BRASSICACEAE 0.0 3.1 0.5 0.4 0.0 Callitris 0.0 0.4 0.5 0.8 0.0 Casuarina 0.0 0.0 0.2 0.0 0.0 Codonocarpus cotinifolius 0.0 0.0 0.5 0.4 0.3 Cycnogeton dubium 3.8 7.8 3.7 2.4 4.7 CYPERACEAE 1.3 9.3 38.7 1.6 4.7 Dodonaea 1.3 0.0 0.2 0.4 0.7 Elaeocarpus 0.0 0.0 0.2 0.0 0.0 Eremophila 0.0 0.0 0.0 0.0 0.3 Euphorbia 0.0 0.0 0.0 0.4 0.0 Ficus 3.8 0.4 1.2 0.4 0.3 Gomphrena 0.0 1.2 0.2 0.4 0.0 Mallotus 0.0 0.0 0.0 0.4 0.0 MALVACEAE 0.0 0.0 0.0 0.0 0.0 Monolete fern spore 0.6 5.8 2.1 4.5 2.0 Myriophyllum 0.0 0.0 0.2 0.4 0.0 MYRTACEAE 8.8 35.4 11.1 5.3 25.3 Newcastelia cladotricha 0.0 0.4 0.0 0.0 0.0 Pandanus 30.0 7.4 4.2 33.5 0.0 Plantago 1.9 0.4 0.5 1.6 0.3 Plectranthus congestus 0.6 0.0 0.0 0.0 0.0 POACEAE 12.5 22.2 27.3 16.7 56.7 Polygonum 0.0 0.0 0.0 0.0 0.3 PROTEACEAE 0.0 0.0 0.0 0.0 0.0 Terminalia 0.0 1.2 0.7 0.0 0.7 Timonius timon 16.9 3.1 1.4 11.4 0.0 Tribulus 0.0 0.0 0.7 0.0 0.0 Trilete fern spore 0.0 0.0 0.0 0.0 0.3 Typha 0.0 0.0 0.2 0.0 2.0 VERBENACEAE 0.0 0.0 0.2 0.0 0.0

Pseudoschizaea 3.0 3.0 1.0 2.0 5.0

254

Appendix 4. Humification data (% transmission and residuals) for BSP00

Depth (cm) % Transmission Residuals Depth (cm) % Transmission Residuals 0.3 32.4 -0.2 60.1 32.5 15.0 1.0 31.8 -0.3 61.0 32.8 14.9 2.0 29.2 -0.2 62.1 32.0 15.5 3.3 30.4 -0.8 63.1 32.0 18.0 4.4 27.8 0.1 64.1 37.7 17.1 5.2 30.4 1.9 65.0 26.9 16.7 6.2 34.5 4.0 66.1 28.3 14.6 7.3 33.0 4.6 67.1 29.1 15.3 8.4 31.4 2.6 68.8 27.0 15.2 9.4 27.8 2.1 70.7 25.8 18.5 10.4 31.3 1.2 72.6 37.3 22.9 11.3 28.5 2.4 74.5 38.3 28.2 12.3 31.4 1.5 76.4 40.0 27.8 13.2 28.7 0.8 80.3 34.8 28.1 14.2 26.7 0.5 82.2 37.0 26.5 15.6 31.1 2.3 84.1 34.7 23.9 16.5 34.4 3.5 86.0 26.4 20.3 17.6 31.0 2.8 87.9 26.4 16.1 18.6 29.8 0.6 91.7 22.4 12.9 19.6 28.5 -0.2 93.6 18.6 12.6 20.5 29.3 0.4 95.5 26.7 12.6 21.6 32.1 0.6 97.4 24.6 11.8 22.5 29.9 1.9 99.4 18.6 7.6 23.5 33.7 -1.0 101.3 16.9 2.7 24.6 24.3 -5.8 103.2 13.4 -0.8 25.6 16.1 -6.1 105.1 12.5 -2.3 27.0 33.3 -4.7 107.0 17.1 -2.7 28.0 29.0 4.2 108.9 17.5 -3.8 29.0 43.5 0.2 110.8 15.2 -7.7 30.0 21.6 -2.1 114.6 12.2 -13.0 31.1 22.4 -7.1 116.6 17.6 -14.3 32.3 28.5 -11.1 118.5 20.7 -15.8 33.4 9.8 -15.0 120.4 17.5 -19.4 34.5 10.7 -20.2 122.3 17.9 -23.8 35.6 12.6 -18.6 124.2 19.3 -27.5 36.7 14.2 -11.4 126.1 19.2 -32.6 37.8 32.0 -4.2 128.0 16.7 -39.3 38.8 33.6 -0.4 129.9 14.3 -46.1 39.8 25.2 -0.4 131.8 14.8 -52.9 40.9 31.2 -6.6 133.7 13.7 -59.8 41.8 13.8 -4.1 135.7 12.0 -69.3 42.8 31.7 -3.8 137.6 6.1 -77.3 43.8 31.0 2.7 139.5 10.6 -85.0 44.8 32.2 4.9 141.4 11.4 -91.4 46.8 36.6 11.4 143.3 10.7 -99.6 47.7 49.1 13.0 145.2 11.3 -108.8 48.7 35.1 17.4 147.1 10.5 -118.2 49.8 48.0 8.5 149.0 10.7 -128.5 50.8 20.7 7.0 150.9 10.2 -139.2 52.0 28.6 -0.5 152.8 10.0 -150.5 53.1 23.5 5.0 154.8 9.9 -162.4 54.1 34.8 6.5 156.7 9.3 -174.7 55.1 30.9 13.3 158.6 10.0 -187.7 56.0 41.7 14.0 160.5 9.4 -201.2 57.1 34.4 17.8 162.4 9.3 -214.8 58.1 40.0 16.4 165.3 11.4 -237.0 59.1 35.0 16.6

255

Appendix 5. LOI data (% organic) for all samples mentioned in text

BSP00

Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic 0.3 69.4 30.6 46.3 62.1 56.9 114.6 17.1 0.6 67.9 31.1 54.2 62.5 38.1 115.6 24.1 1.0 71.6 31.7 39.8 63.1 59.6 116.6 23.9 1.4 70.7 32.3 58.5 63.6 61.6 117.5 16.2 2.0 71.6 32.9 32.0 64.1 64.7 118.5 25.3 2.6 70.9 33.4 23.5 64.6 53.0 119.4 24.8 3.3 72.9 33.9 15.0 65.0 53.7 120.4 21.3 4.0 71.0 34.5 22.0 65.6 53.3 121.3 19.6 4.4 70.1 35.1 29.0 66.1 50.0 122.3 21.7 4.8 70.9 35.6 28.7 66.6 50.9 123.2 25.5 5.2 73.3 36.0 34.5 67.1 47.9 124.2 23.8 5.8 75.4 36.7 32.9 67.6 60.1 125.1 23.5 6.2 77.5 37.1 31.2 68.8 42.8 126.1 23.8 6.8 77.4 37.8 77.1 69.8 38.2 127.1 20.6 7.3 72.1 38.3 74.8 70.7 38.4 128.0 20.7 7.7 70.7 38.8 81.5 71.7 48.2 129.0 18.7 8.4 70.0 39.4 82.5 72.6 58.3 129.9 16.8 9.0 69.7 39.8 56.1 73.6 43.3 130.9 17.3 9.4 65.5 40.4 82.3 74.5 56.3 131.8 17.0 9.9 70.9 40.9 74.9 75.5 53.3 132.8 16.4 10.4 70.7 41.2 68.2 76.4 56.5 133.7 15.6 10.8 69.8 41.8 38.0 77.4 54.2 134.7 14.7 11.3 71.2 42.4 59.4 78.4 51.8 135.7 13.6 11.8 70.5 42.8 77.5 79.3 48.3 136.6 11.9 12.3 69.8 43.3 80.4 80.3 48.3 137.6 6.8 12.8 69.8 43.8 72.9 81.2 38.8 138.5 12.6 13.2 68.4 44.3 78.9 82.2 51.4 139.5 11.7 13.7 69.7 44.8 68.5 83.1 48.7 140.4 12.1 14.2 66.2 46.3 80.0 84.1 52.2 141.4 12.0 14.9 70.0 46.8 86.2 85.0 43.9 142.3 11.0 15.6 71.2 47.3 84.8 86.0 38.9 143.3 11.5 16.0 73.0 47.7 92.4 86.9 41.9 144.2 11.7 16.5 77.3 48.2 81.7 87.9 40.0 145.2 11.8 17.0 75.0 48.7 78.8 88.9 47.1 146.2 11.2 17.6 73.8 49.2 79.5 89.8 44.8 147.1 11.2 18.1 70.4 49.8 88.6 90.8 38.1 148.1 13.5 18.6 70.2 50.3 74.4 91.7 31.9 149.0 11.5 19.0 69.6 50.8 47.2 92.7 31.8 150.0 11.7 19.6 67.8 51.3 50.6 93.6 25.1 150.9 10.9 20.0 69.0 52.0 51.0 94.6 23.3 151.9 10.5 20.5 68.6 52.6 51.0 95.5 36.8 152.8 10.6 21.0 68.8 53.1 47.7 96.5 35.2 153.8 10.2 21.6 73.9 53.6 47.5 97.4 36.9 154.8 10.4 22.1 73.4 54.1 56.0 98.4 28.7 155.7 9.9 22.5 70.1 54.6 57.4 99.4 24.3 156.7 9.8 23.1 72.0 55.1 59.1 100.3 22.6 157.6 9.6 23.5 71.8 55.6 62.5 101.3 21.5 158.6 10.4 24.1 71.4 56.0 64.2 102.2 18.1 159.5 10.4 24.6 57.8 56.6 59.7 103.2 15.3 160.5 9.9 25.1 57.7 57.1 60.6 104.1 16.7 161.4 9.9 25.6 38.5 57.5 58.9 105.1 15.1 162.4 9.8 26.3 41.1 58.1 61.7 106.0 18.0 163.3 10.4 27.0 79.9 58.6 58.9 107.0 19.5 165.3 11.9 27.5 45.0 59.1 54.5 108.0 21.7 28.0 65.5 59.6 62.5 108.9 20.9 28.4 79.3 60.1 55.5 109.9 17.4 29.0 89.6 60.6 60.4 110.8 18.3 29.5 73.8 61.0 61.3 111.8 20.5 30.0 46.0 61.6 56.7 113.7 19.9

256

BSP02 Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic 2.5 97.3 64.0 68.6 125.0 37.1 188.0 11.8 4.5 79.8 65.0 68.3 126.0 54.2 189.0 10.7 6.0 72.4 66.0 64.4 127.0 58.3 190.0 13.7 7.0 68.2 67.0 70.2 128.0 54.9 191.0 12.8 8.0 70.5 68.0 60.7 129.0 26.1 192.0 10.8 9.0 68.1 69.0 63.9 130.0 31.1 193.0 12.1 10.0 68.8 70.0 68.2 131.0 39.5 194.0 19.5 11.0 64.5 71.0 63.0 132.0 20.8 195.0 14.5 12.0 66.3 72.0 62.9 133.0 35.7 196.0 12.1 13.0 66.4 73.0 58.3 134.0 30.8 197.0 12.4 14.0 68.4 74.0 59.9 135.0 33.4 198.0 9.9 15.0 68.2 75.0 57.1 136.0 45.2 199.0 8.9 16.0 68.0 76.0 58.9 137.0 48.9 200.0 9.4 17.0 68.2 77.0 58.6 138.0 55.6 201.0 9.0 18.0 69.8 78.0 59.1 139.0 51.1 202.0 8.8 19.0 68.6 79.0 62.6 140.0 54.2 203.0 8.4 20.0 70.2 80.0 62.3 141.0 47.8 204.0 9.5 21.0 73.8 81.0 56.7 142.0 51.2 205.0 9.0 22.0 68.6 82.0 50.1 143.0 52.8 207.0 9.5 23.0 68.0 83.0 45.5 144.0 47.6 208.0 7.3 24.0 68.5 84.0 47.2 145.0 38.1 209.0 8.4 25.0 70.1 85.0 46.7 146.0 30.9 210.0 8.1 26.0 70.7 86.0 41.1 147.0 49.1 211.0 7.1 27.0 67.9 87.0 42.2 148.0 44.8 212.0 10.7 28.0 69.9 88.0 45.8 149.0 49.2 213.0 8.3 29.0 68.4 89.0 46.5 150.0 47.1 214.0 9.9 30.0 70.4 90.0 48.7 151.0 43.0 215.0 7.9 31.0 69.4 91.0 45.2 152.0 40.5 216.0 8.6 32.0 71.1 92.0 38.4 153.0 51.7 217.0 8.7 33.0 67.6 93.0 47.3 154.0 38.3 218.0 8.2 34.0 68.9 94.0 48.7 155.0 35.4 219.0 7.7 35.0 70.5 95.0 50.2 156.0 39.4 220.0 7.4 36.0 72.4 96.0 52.7 157.0 38.8 221.0 8.6 37.0 70.8 97.0 45.3 158.0 34.9 222.0 7.4 38.0 71.7 98.0 53.2 159.0 36.7 223.0 7.9 39.0 70.0 99.0 52.3 160.0 39.2 224.0 7.9 40.0 70.8 100.0 54.9 161.0 38.9 225.0 9.0 41.0 72.8 101.0 57.7 162.0 41.3 226.0 7.3 42.0 70.6 102.0 56.2 163.0 45.5 227.0 7.5 43.0 71.9 103.0 57.5 164.0 41.3 228.0 8.4 44.0 72.0 104.0 46.5 165.0 43.5 229.0 8.8 45.0 70.8 105.0 39.2 166.0 41.6 230.0 7.8 46.0 67.3 106.0 24.6 167.0 37.2 231.0 7.4 47.0 70.5 107.0 39.0 168.0 35.7 232.0 7.7 48.0 71.9 108.0 48.2 169.0 31.2 233.0 7.8 49.0 70.3 109.0 45.0 170.0 36.0 234.0 7.1 50.0 73.0 111.0 52.5 171.0 25.3 235.0 7.1 51.0 70.4 112.0 52.7 172.0 30.8 236.0 7.2 52.0 69.6 113.0 48.6 173.0 17.4 237.0 7.6 53.0 57.7 114.0 52.0 174.0 27.9 238.0 8.4 54.0 61.6 115.0 54.8 175.0 17.6 239.0 9.5 55.0 66.5 116.0 42.9 176.0 16.9 240.0 8.6 56.0 64.3 117.0 52.5 177.0 17.5 241.0 8.9 57.0 72.6 118.0 37.3 178.0 18.4 242.0 8.3 58.0 63.9 119.0 35.5 179.0 17.2 243.0 8.1 59.0 67.0 120.0 37.7 180.0 19.0 60.0 63.1 121.0 36.5 181.0 17.7 61.0 66.9 122.0 44.6 182.0 16.5 62.0 69.8 123.0 37.2 183.0 17.6 63.0 64.6 124.0 33.5 184.0 15.0

257

ELZ01

Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic 0.0 51.4 57.5 11.3 111.5 4.4 1.0 54.7 58.5 9.6 112.5 3.8 3.0 47.3 59.5 9.8 113.5 4.3 5.0 44.3 60.5 9.8 114.5 4.1 6.0 42.8 61.5 10.0 115.5 5.0 7.0 38.9 62.5 9.7 116.5 4.6 9.0 42.4 63.5 9.4 117.5 4.5 10.0 42.4 64.5 9.5 118.5 4.4 11.0 37.2 65.5 8.9 119.5 4.4 13.0 36.4 66.5 8.8 120.5 5.8 14.0 35.6 67.5 8.6 121.5 5.3 15.0 37.1 68.5 8.3 122.5 4.5 16.0 36.4 69.5 7.6 123.5 3.2 17.0 34.4 70.5 8.1 124.5 2.7 18.0 35.4 71.5 7.8 125.5 3.2 19.0 34.1 72.5 7.8 126.5 3.2 20.0 30.9 73.5 8.0 127.5 2.5 21.0 32.0 74.5 8.3 128.5 1.3 22.0 31.5 75.5 7.8 129.5 1.3 23.0 26.9 76.5 7.6 130.5 1.0 24.0 26.3 77.5 7.8 131.5 1.1 25.0 24.7 78.5 7.0 132.5 0.7 26.0 23.8 79.5 7.2 133.5 0.6 27.0 20.6 80.5 6.2 134.5 0.7 28.0 18.8 81.5 5.3 29.0 17.0 82.5 5.8 30.0 17.0 83.5 5.5 31.0 17.6 84.5 4.4 32.0 15.9 86.5 4.3 33.0 17.6 87.5 4.2 34.0 17.5 88.5 4.6 35.0 17.7 89.5 5.8 36.0 17.6 90.5 9.7 37.0 16.9 91.5 9.4 38.0 16.2 92.5 9.3 39.0 16.3 93.5 9.3 40.0 15.6 94.5 9.3 41.0 15.3 95.5 9.1 42.0 15.2 96.5 9.0 43.0 14.6 97.5 9.2 44.0 15.0 98.5 9.4 45.0 14.0 99.5 9.2 46.0 13.7 100.5 9.6 47.0 14.5 101.5 9.1 48.0 12.8 102.5 8.5 49.5 13.3 103.5 8.4 50.5 14.7 104.5 9.0 51.5 11.7 105.5 8.2 52.5 14.7 106.5 7.6 53.5 11.3 107.5 7.8 54.5 11.0 108.5 7.7 55.5 10.8 109.5 6.4 56.5 10.1 110.5 5.5

258

FRN02

Depth (cm) % organic Depth (cm) % organic Depth (cm) % organic 0.0 33.6 67.0 44.8 134.0 10.0 1.0 50.7 68.0 44.1 135.0 9.5 2.0 53.4 69.0 40.6 136.0 8.6 3.0 53.2 70.0 44.0 137.0 9.7 4.0 69.6 71.0 39.6 138.0 9.9 5.0 61.5 72.0 38.4 139.0 8.8 6.0 69.5 73.0 36.3 140.0 9.7 7.0 66.0 74.0 39.4 141.0 10.7 8.0 68.9 75.0 37.3 142.0 7.9 9.0 72.1 76.0 41.6 143.0 7.7 10.0 70.2 77.0 42.0 144.0 5.8 11.0 68.0 78.0 43.4 145.0 7.3 12.0 62.8 79.0 43.1 146.0 6.9 13.0 59.7 80.0 43.8 147.0 7.0 14.0 60.0 81.0 42.6 148.0 8.1 15.0 59.7 82.0 41.5 149.0 9.6 16.0 57.6 83.0 43.4 150.0 8.6 17.0 56.5 84.0 40.7 151.0 8.3 18.0 56.9 85.0 42.4 152.0 8.8 19.0 57.1 86.0 46.7 153.0 8.6 20.0 58.5 87.0 44.8 154.0 11.7 21.0 57.0 88.0 48.8 155.0 17.8 22.0 53.1 89.0 50.6 156.0 16.4 23.0 52.9 90.0 52.0 157.0 17.4 24.0 53.9 91.0 50.0 158.0 11.9 25.0 45.8 92.0 47.8 159.0 7.9 26.0 49.6 93.0 50.4 160.0 7.6 27.0 51.4 94.0 42.2 161.0 7.0 28.0 52.3 95.0 41.4 162.0 8.0 29.0 49.4 96.0 40.8 163.0 9.0 30.0 52.2 97.0 41.5 164.0 7.0 31.0 49.1 98.0 40.9 165.0 8.4 32.0 37.3 99.0 45.3 166.0 8.0 33.0 44.1 100.0 47.0 167.0 8.1 34.0 48.6 101.0 46.9 168.0 7.7 35.0 57.4 102.0 43.4 169.0 9.2 36.0 58.6 103.0 39.8 170.0 6.9 37.0 59.3 104.0 39.1 171.0 7.1 38.0 58.1 105.0 40.8 172.0 8.9 39.0 59.8 106.0 40.2 173.0 8.5 40.0 65.4 107.0 38.4 174.0 10.9 41.0 60.9 108.0 33.6 175.0 7.4 42.0 63.4 109.0 29.6 176.0 8.8 43.0 52.4 110.0 31.4 177.0 9.2 44.0 56.2 111.0 30.4 178.0 7.8 45.0 52.9 112.0 30.8 179.0 7.5 46.0 54.9 113.0 31.9 180.0 6.0 47.0 54.6 114.0 32.2 181.0 5.7 48.0 54.4 115.0 31.6 182.0 6.0 49.0 45.2 116.0 39.0 183.0 5.8 50.0 48.6 117.0 39.8 184.0 6.3 51.0 48.8 118.0 36.3 185.0 7.0 52.0 49.6 119.0 36.6 186.0 6.2 53.0 48.9 120.0 37.6 187.0 6.1 54.0 49.6 121.0 37.5 188.0 6.9 55.0 47.9 122.0 39.9 189.0 5.6 56.0 49.6 123.0 36.1 190.0 6.5 57.0 57.3 124.0 34.3 191.0 6.3 58.0 50.3 125.0 33.1 192.0 6.4 59.0 46.3 126.0 27.6 193.0 6.3 60.0 47.0 127.0 24.8 194.0 7.6 61.0 46.8 128.0 16.1 195.0 8.4 62.0 43.8 129.0 11.9 196.0 9.4 63.0 42.0 130.0 14.2 199.5 9.5 64.0 42.7 131.0 11.1 202.0 9.1 65.0 44.5 132.0 10.0 203.0 9.5 66.0 42.5 133.0 10.1 259

Appendix 6. 210Pb results including age calculations using both the CIC and CRS models

BSP02

ANSTO Depth Error Total 210Pb Error Supported Error Unsupported Error Calculated Error Calculated Error ID (cm) (Bq/kg) 210Pb (Bq/kg) 210Pb (Bq/kg) CIC ages CRS ages (yrs BP) (yrs BP) R535 0.25 0.25 963.75 45.30 810.62 70.58 153.20 83.91 4 4 4 2 R536 0.75 0.25 922.17 48.94 851.73 69.65 70.47 85.16 17 9 13 17 R537 1.25 0.25 603.89 31.94 525.78 44.03 78.16 54.43 32 14 24 18 R538 1.75 0.25 605.01 36.99 483.59 42.64 121.48 56.48 45 19 43 21 R539 2.75 0.25 960.72 47.87 950.16 75.40 10.57 89.36 76 31 117 55 R540 3.75 0.25 540.23 26.48 753.30 60.53 -213.18 66.10 R541 4.75 0.25 654.43 32.99 703.62 58.14 -49.22 66.88 R542 6.75 0.25 608.32 26.69 663.13 52.78 -54.84 59.18 ELZ01

ANSTO Depth Error Total 210Pb Error Supported Error Unsupported Error Calculated Error Calculated Error ID (cm) (Bq/kg) 210Pb (Bq/kg) 210Pb (Bq/kg) CIC ages CRS ages (yrs BP) (yrs BP) R527 0.25 0.25 1892.82 84.75 273.35 26.09 1620.16 88.71 1.53 1.53 1.39 1.18 R528 0.75 0.25 649.98 27.63 166.90 17.71 483.29 32.83 R529 1.25 0.25 1246.64 52.56 142.47 13.36 1104.64 54.25 7.44 1.65 6.04 2.46 R530 1.75 0.25 1016.08 42.20 93.10 9.47 923.38 43.27 10.08 1.73 7.77 2.79 R531 2.75 0.25 1074.60 43.95 99.38 8.95 975.63 44.87 16.09 2.11 11.80 3.44 R532 3.75 0.25 745.39 29.75 87.87 8.90 657.81 31.06 22.63 2.62 16.04 4.00 R533 4.75 0.25 381.39 14.60 127.35 11.31 254.14 18.47 R534 6.75 0.25 608.18 24.28 178.88 15.44 429.48 28.79 44.55 4.53 28.14 5.30 S150 7.75 0.25 481.78 21.23 219.07 19.61 266.62 29.33 52.10 5.21 31.54 0.00 R891 10.25 0.25 443.18 23.05 314.30 32.46 129.89 40.12 S151 12.75 0.25 481.50 20.07 215.66 18.09 269.79 27.42 R892 15.25 0.25 511.50 26.99 205.98 20.59 307.90 34.21 S152 17.75 0.25 562.21 24.13 182.22 15.14 385.63 28.91 R893 20.25 0.25 378.78 18.88 344.29 38.36 34.76 43.09 S153 22.75 0.25 554.54 23.51 291.35 25.71 267.10 35.36 R894 25.25 0.25 366.77 19.71 465.02 51.04 -99.02 55.14 S154 27.75 0.25 550.11 22.98 294.53 23.69 259.38 33.49 R895 30.25 0.25 493.75 21.23 421.08 40.54 73.23 46.12

FRN02

ANSTO Depth Error Total 210Pb Error Supported Error Unsupported Error ID (cm) (Bq/kg) 210Pb (Bq/kg) 210Pb (Bq/kg) R543 0.25 0.25 397.67 16.42 487.31 41.99 -89.72 45.13 R544 0.75 0.25 417.11 21.45 366.07 38.80 51.10 44.38 R545 1.25 0.25 528.98 29.56 340.09 32.56 189.08 44.02 R546 1.75 0.25 454.02 19.26 283.46 26.39 170.73 32.71 R547 2.75 0.25 649.29 26.35 329.25 29.16 320.37 39.34 R548 3.75 0.25 442.02 22.18 234.06 23.99 208.18 32.71 R549 4.75 0.25 481.72 21.51 220.79 21.00 261.19 30.10 R550 6.75 0.25 621.59 41.08 181.17 33.99 440.87 53.37

260

Appendix 7. 239+240Pu results

BSP02

Oz Depth Error 240/239 ratio Error 239+240Pu activity Error number (cm) (RHS) (mBq/g) (LHS) 6472 1.25 0.25 0.19654 0.00972 0.07260 0.00171 6473 1.75 0.25 0.11993 0.00789 0.03792 0.00111 6474 2.25 0.25 0.12006 0.00911 0.04684 0.00157 6475 3.25 0.25 0.12244 0.00713 0.04378 0.00118 6476 5.25 0.25 0.12228 0.00529 0.07976 0.00169 6477 8.25 0.25 0.11421 0.00404 0.13416 0.00255 ELZ01

Oz Depth Error 240/239 ratio Error 239+240Pu activity Error number (cm) (RHS) (mBq/g) (LHS) 6462 0.75 0.25 0.11568 0.00386 0.17510 0.00307 6463 2.25 0.25 0.11685 0.00414 0.28842 0.00526 6464 3.75 0.25 0.11565 0.00385 0.35965 0.00635 6465 4.25 0.25 0.12234 0.00372 0.40406 0.00649 6466 4.75 0.25 0.11742 0.00379 0.45357 0.00783 6467 5.25 0.25 0.11330 0.00348 0.54808 0.00921 6468 6.25 0.25 0.11606 0.00341 0.61595 0.00981 6469 8.25 0.25 0.12466 0.00405 0.65776 0.01123 6470 12.25 0.25 0.07885 0.00272 0.41881 0.00778

261

Appendix 8. Elemental composition (% by weight) of charcoal fragments derived from SEM and EDXA

Sample ID Carbon Oxygen Sodium Silicon Aluminium Phosphorus T910 64.7 32.8 2.5 0.0 0.0 0.0 T911 67.3 32.7 0.0 0.0 0.0 0.0 T912 56.6 42.4 0.5 0.5 0.0 0.0 T913 65.8 34.2 0.0 0.0 0.0 0.0 T914 55.7 37.3 3.0 0.0 2.6 1.4 T915 54.2 41.1 0.0 0.0 3.8 0.8 T916 62.6 29.9 1.3 0.0 3.8 2.4 T917 29.1 51.0 2.4 4.4 8.0 5.1 T918 66.7 28.0 1.2 2.1 1.2 0.9 T919 39.7 43.2 0.0 7.9 7.7 1.4

262

Appendix 9. Ln/Tn data for BSP02

L /T L /T Natural Natural Signal Test Signal Test Signal Depth (cm) n n n n (BSL) (IRSL ) Signal (BSL) (IRSL) (BSL) (IRSL) 5 0.03 0.33 63 729 332 1245 5 0.02 0.12 73 522 705 679 5 0.06 1 102 663 755 707 15 0.43 1.07 174 950 293 888 15 0.29 1.45 87 704 163 688 15 0.51 0.62 126 595 196 600 22 0.34 1.93 374 910 980 726 22 0.26 0.64 202 644 611 745 22 0.33 1.73 404 1112 1078 842 35 0.29 0.54 687 812 2213 1077 35 0.38 0.91 339 688 805 720 35 0.29 1.39 326 894 998 812 40 0.45 0.73 644 571 1368 591 40 0.49 1.22 327 532 610 527 40 0.48 0.8 563 584 1126 617 46 0.28 0.43 820 880 2506 1218 46 0.18 0.48 864 945 3972 1367 46 0.36 0.31 682 830 1549 1445 55 0.7 0.97 5192 1676 7412 1781 55 0.76 0.92 7214 2715 9457 2860 55 0.78 0.76 4483 1720 5688 1997 65 0.79 1.36 7273 1945 9208 1609 65 0.74 1.28 9384 2172 12628 1923 65 0.75 1.05 10183 2027 13609 1903 75 0.94 1.16 8850 2939 9437 2656 75 0.97 1.1 9996 2258 10242 2128 75 0.93 1.34 7452 2313 8031 1915 85 2.43 3.53 72998 13580 30174 4419 85 2.56 3.62 87120 27664 34113 8090 85 2.41 3.34 103055 13030 42871 4382 95 3.69 6.13 47799 19117 13039 3703 95 3.81 6.18 75846 22527 20018 4239 95 3.83 5.95 56729 34534 14892 6456 105 2.84 3.82 49637 11660 17521 3545 105 2.99 3.29 70615 14301 23711 4847 105 2.92 2.95 63718 14729 21896 5417

263

L /T L /T Natural Natural Signal Test Signal Test Signal Depth (cm) n n n n (BSL) (IRSL ) Signal (BSL) (IRSL) (BSL) (IRSL) 115 5.09 7.35 79280 19672 15676 3301 115 6.08 7.18 67836 15285 11251 2746 115 5.22 7.11 43882 10730 8481 2100 125 3.49 4.95 32796 2429 9441 881 125 4.61 5.46 37816 13405 8257 2923 125 3.75 6.64 24609 3158 6614 998 135 5.27 6.59 25947 28078 5000 4829 135 5.54 7.23 28566 32581 5238 5099 135 5.11 5.62 57242 55655 11293 10570 145 3.68 4.55 79056 23401 21571 5634 145 4.02 5.98 54657 27988 13684 5276 145 4.2 5.28 27059 13035 6517 2955 155 4.21 4.94 72195 50777 17262 10935 155 4.61 4.7 94296 79439 20584 17567 155 4.44 5.37 75338 44889 17101 8981 165 4.51 4.99 49580 45666 11087 9813 165 4.26 5.07 44453 32175 10529 7025 165 4.34 4.62 66106 51746 15366 11889 175 5 5.6 55416 55960 11255 10728 175 5.17 5.83 105514 128002 20708 22809 175 5.07 5.91 85335 64830 17029 11665 185 5.05 5.7 87596 64399 17503 12065 185 5.36 6.29 53651 56993 10147 9779 185 5.12 5.06 88537 44208 17440 9361 195 4.1 4.19 136508 39444 33497 9923 195 4.48 4.84 53355 45765 12070 10036 195 4.48 4.74 63241 43965 14269 9907 205 4.3 4.49 60853 22031 14241 5526 205 4.05 3.64 82910 9377 20582 3065 205 4.33 4.34 69326 25776 16110 6512 215 4.92 4.29 74519 32352 15281 8128 215 5.5 5.14 103285 49037 18933 10197 215 5.07 5.77 67331 23503 13435 4732 225 4.95 5.22 67243 36173 13738 7522 225 5.16 5.28 84222 48928 16592 9925 225 5.84 5.57 86407 55276 14976 10573 235 5.52 5.85 47377 38890 8708 7313 235 5.24 5.64 109711 32138 21079 6312 235 5.49 6.44 62209 40917 11499 7011

264

Appendix 10. PCA axis 1 scores for pollen and NPP datasets for all samples mentioned in the text

Pollen

BSP02 ELZ01 FRN02

Depth (cm) PCA axis 1 score Depth (cm) PCA axis 1 score Depth (cm) PCA axis 1 score 4.0 -0.55 0.0 0.26 0.5 1.58 10.0 -0.53 5.0 0.38 10.0 -0.57 20.0 -0.36 10.0 4.29 20.0 -1.35 30.0 0.11 15.0 0.29 30.0 -0.58 40.0 -0.83 20.0 -0.28 40.0 -0.75 50.0 -0.71 25.0 -0.17 50.0 0.10 60.0 0.19 30.0 0.18 60.0 0.17 70.0 -0.47 35.0 0.02 70.0 0.28 80.0 -1.88 40.0 1.83 80.0 3.00 90.0 -1.21 45.5 -0.51 90.0 0.15 100.0 -0.44 51.5 -0.04 100.0 -0.65 110.0 -0.29 56.5 -0.21 110.0 0.59 120.0 -0.07 61.5 -0.01 120.0 1.56 130.0 -0.11 66.5 -0.21 130.0 -0.12 140.0 -0.60 71.5 0.04 140.0 0.29 150.0 -0.72 76.5 -0.47 150.0 -0.47 160.0 0.69 81.5 -0.52 160.0 -1.12 170.0 2.18 86.5 -0.56 170.0 -0.92 180.0 2.85 91.5 -0.51 180.5 -0.28 190.0 1.10 97.0 -0.50 190.5 -0.15 200.0 1.05 101.5 -0.54 199.5 -0.77 210.0 0.93 106.5 -0.40 220.0 0.09 111.5 -0.93 230.0 0.00 116.5 -0.77 240.0 -0.38 121.5 -0.34 126.5 -0.31

265

NPPs

BSP02 ELZ01 FRN02

Depth (cm) PCA axis 1 score Depth (cm) PCA axis 1 score Depth (cm) PCA axis 1 score 4.0 0.01 0.0 -0.18 0.5 3.18 10.0 0.60 5.0 4.94 10.0 0.71 20.0 1.41 10.0 -0.19 20.0 0.92 30.0 3.39 15.0 0.53 30.0 -0.10 40.0 1.95 20.0 -0.30 40.0 2.24 50.0 1.42 25.0 -0.31 50.0 -0.26 60.0 0.07 30.0 -0.23 60.0 -0.35 70.0 0.46 35.0 -0.16 70.0 0.57 80.0 -0.41 40.0 -0.24 80.0 -0.53 90.0 -0.59 45.5 -0.23 90.0 -0.38 100.0 -0.38 51.5 -0.26 100.0 -0.06 110.0 -0.51 56.5 -0.21 110.0 -0.62 120.0 -0.51 61.5 -0.23 120.0 -0.34 130.0 -0.58 66.5 -0.22 130.0 -0.56 140.0 -0.46 71.5 -0.22 140.0 -0.64 150.0 -0.57 76.5 -0.24 150.0 -0.65 160.0 -0.59 81.5 -0.23 160.0 -0.66 170.0 -0.58 86.5 -0.23 170.0 -0.65 180.0 -0.59 91.5 -0.23 180.5 -0.57 190.0 -0.59 97.0 -0.23 190.5 -0.62 200.0 -0.59 101.5 -0.23 199.5 -0.61 210.0 -0.58 106.5 -0.23 220.0 -0.59 111.5 -0.23 230.0 -0.59 116.5 -0.23 240.0 -0.59 121.5 -0.23 126.5 -0.23

266