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An Annually Resolved Climate Record for MIS 11 from Marks Tey, Eastern

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An Annually Resolved Climate Record for MIS 11 from Marks Tey, Eastern An annually resolved climate record for MIS 11 from Marks Tey, eastern England: Investigating landscape response to abrupt events during the closest climatic analogue to the Holocene Gareth Jonathan Tye Thesis submitted for the degree of Doctor of Philosophy, Royal Holloway, University of London March 2015 Institution of study: Centre for Quaternary Research Department of Geography Royal Holloway University of London Declaration of Authorship I, Gareth Jonathan Tye, hereby declare that this thesis and the work presented in it is entirely my own. Where I have consulted the work of others, this is always clearly stated. Signed: Contents Abstract Climatic and environmental reconstructions from previous interglacial episodes of the Quaternary Period are of significant interest, as previous interglacials may have the potential to act as analogues for the Holocene. Based on the similarity in long-term insolation patterns during both interglacials, Marine Isotope Stage 11 (MIS 11, ca. 410,000 yrs BP.) is widely considered to offer the best orbital analogue for the Holocene. The palaeo-lake sequence at Marks Tey, eastern England, represents one of the key MIS 11 sites in the UK and Europe because not only does it record a full vegetation succession for the interglacial at a single site, the sediments are also purportedly annually-laminated (varved) in parts of the sequence (Turner, 1970). Furthermore, the vegetation succession is interrupted during full interglacial conditions by an abrupt event (the Non-Arboreal Pollen (NAP) phase), which may be analogues to the 8.2 ka event that punctuated the early Holocene (Koutsodendris et al., 2012). This thesis presents a re-examination of the early Hoxnian (MIS 11) sequence from a new core drilled at Marks Tey in 2010, providing discussion of: 1) Micro-facies analysis of the laminated sediments preserved during the early part of MIS 11; to demonstrate the annual nature of sedimentation and produce a varve chronology; 2) Results of stable oxygen and carbon isotopic analysis from authigenic carbonate laminations that occur throughout the core section studied and their environmental significance; and 3) Combining the varve chronology and stable isotope results with other proxy evidence to investigate the timing and forcing mechanism for, as well as the rate of proxy response during the NAP phase. 1 Contents Acknowledgements First and foremost, I wish to thank my supervisors Dr I. Candy and Dr A. Palmer for their endless encouragement, support and patience over the last four years. Thank you to all of the staff of the CQR for their discussions and useful insights, and for making the department such a great place to be. I would like to thank Prof. Pete Coxon (TCD) for his work on producing the pollen record for the new core, as well as Dr Mark Hardiman (Portsmouth) for providing the charcoal counts and Dr Dave Ryves and Katie Loakes for undertaking the diatom analysis. I would also like to thank Prof. Anson Mackay (UCL) for supervising the diatom work that I undertook as part of this project. Dr Ian Matthews is thanked for useful discussions about statistics and Dr Dave Lowry is thanked for running the isotope samples. I would also like to thank Maurice Page (W.H. Collier Ltd) for allowing us to core the site, and Ecologia Ltd. for undertaking the coring. A huge thanks is due to the RHUL geography laboratory and support staff Iñaki Valcarcel, Robyn Christie, Jenny Kynaston and Elaine Turton for all of their assistance over the last four years. Thanks to all of the CQR PhD students for making my time at RHUL so enjoyable; and a special thanks to Jenni Sherriff, Paul Lincoln, Chris Satow and Mark Hardiman for all of their support and making the past four years so enjoyable! This thesis is dedicated to my family and to Claire Gallant for their endless support and for always believing in me. Thank you. 2 Contents List of contents Abstract 1 Acknowledgements 2 List of contents 3 List of figures 10 List of tables 15 Chapter 1 - Introduction 17 1.1 Scientific rationale 17 1.1.1 Varved lake sequences 19 1.1.2 Lacustrine stable isotope records 20 1.2 Site introduction and previous work 21 1.3 Aims and Objectives 23 1.3.1 Aims 23 1.3.2 Objectives 24 1.4 Thesis structure 25 Chapter 2 – Marine Isotope Stage 11 27 2.1. Introduction 28 2.2. MIS 11 as an analogue for the Holocene 31 2.3. Climatic structure of MIS 11 35 2.3.1. Ice core and stacked marine records 35 2.3.2. North Atlantic marine records 37 2.3.3. Climatic structure of MIS 11 in the British Isles 40 2.4. Abrupt events during MIS 11 43 2.4.1. Identification of abrupt events in MIS 11 sequences 44 2.4.1.1. The British Isles 46 2.4.1.2. Continental Europe 47 2.4.1.3. The Mediterranean 47 2.4.2. The OHO/NAP phase: an analogue for early Holocene abrupt climate 48 events? 2.4.2.1. The 8.2ka event 48 2.4.2.2. Rationale of the comparison of the OHO/NAP phase and 8.2 ka 51 event 2.4.2.3. Structure and duration of the OHO/NAP pollen event 53 2.4.2.4. Timing of the OHO/NAP phase 54 2.4.2.5. Potential forcing mechanisms for the OHO/NAP phase 60 2.4.2.6. Duration of the climatic event 63 2.4.2.7. Alternative forcing mechanisms 65 2.5. Summary 66 Chapter 3. Climatic reconstruction using stable isotopes of lacustrine 67 carbonates 3.1. Introduction 68 3.2. Stable isotopes and the formation of carbonate in lacustrine 71 environments 3.2.1. Basic chemical principles 71 3.2.2. Equilibrium, kinetic and non-equilibrium fractionation 73 3 Contents 3.2.3. Isotope measurement and reporting 74 3.2.4. Calcium carbonate formation 75 3.3. Factors that control the δ18O of freshwater carbonates 77 3.3.1. δ18O of rainfall 78 3.3.1.1. Evaporation of source water 79 3.3.1.2. Temperature and latitude 79 3.3.1.3. Contintentality and altitude 80 3.3.1.4. Amount effect, seasonality and atmospheric circulation 82 3.3.2. δ18O of recharge waters 84 3.3.3. δ18O of lacustrine waters 85 3.3.4. Controls over the δ18O of calcite during mineral precipitation 87 3.3.5. Summary: temperature and the δ18O of lake water in temperate 88 regions 3.4. Factors that control the δ13C of freshwater carbonates 88 3.4.1. Lake catchment processes 89 3.4.2. Within-lake processes 90 3.5. Practical issues to consider when interpreting lacustrine stable isotope 91 records 3.5.1. Timing and depth of calcite precipitation 91 3.5.2. (Dis)Equilibrium conditions and digenetic alteration 92 3.5.3. Composition of lacustrine carbonates in sediment cores 92 3.5.4. Core sedimentology and its influence on the isotopic signal 94 3.6. Key lacustrine sequences in the British Isles and Europe 95 3.6.1. Key sequences from the British Isles 97 3.6.2. Key lacustrine sequences from MIS 11 101 3.7. Summary 104 Chapter 4. Varved sediments 105 4.1. Introduction 106 4.2. Preconditions for varve formation 107 4.2.1. Sediment supply and distribution 109 4.2.2. Basin morphometry 111 4.2.3. Thermal stratification of the water column 113 4.3. Varve types 114 4.3.1. Model for varve formation at Marks Tey: calcitic biogenic varves 116 4.3.1.1. Diatom blooms 116 4.3.1.2. Calcite precipitation 118 4.3.1.3. Organic/detrital material 119 4.3.1.4. Examples of other structural components in calcitic biogenic 120 varves 4.4. Determination of the seasonal signal in laminated sediments 121 4.4.1. Micro-facies descriptions 122 4.4.2. Development of a depositional model 123 4.5. Construction of varve chronologies 123 4.5.1. Core collection 124 4.5.2. Counting methods 125 4.5.3. Estimating counting error and chronology validation 127 4.6. The application of varved sediments to the study of abrupt events 129 4.6.1. The 8.2 ka event 129 4 Contents 4.6.2. The Last Glacial to Interglacial Transition 130 4.7. Summary 132 Chapter 5. Methodology 134 5.1. Introduction 134 5.2. Coring, correlation and macro-sedimentology 135 5.2.1. Coring 135 5.2.2. Correlation and macro-sedimentology 137 5.2.3. Calcium carbonate and organic carbon 137 5.2.4. μ-XRF core scanning 137 5.2.4.1 Calibration of μ-XRF data 141 5.3. Investigating whether the laminated sediments in the sequence are 142 varves 5.3.1. Core sampling 143 5.3.2. Diatom preparation 143 5.3.3. Pollen preparation 144 5.3.4. Stable isotope analysis 144 5.3.5. Statistical analysis 144 5.4. Varve micro-facies analysis and chronology construction 145 5.4.1. Thin section micromorphology 145 5.4.2. Chronology construction 147 5.4.2.1. Core collection 148 5.4.2.2. Pre-counting procedure 148 5.4.2.3. Counting procedure 148 5.4.2.4. Error estimation and varve interpolation 149 5.5. Production of a stable isotope stratigraphy for the sequence 150 5.5.1. Core sampling 150 5.5.2. Sample preparation and analysis 151 5.6. Calibrating other proxies using the varve chronology 151 Chapter 6. Stratigraphy, bulk sedimentology and pollen results of the Marks 153 Tey sequence 6.1. Introduction 153 6.2.
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