Cenozoic Antarctic climate evolution based on molecular and isotopic biomarker reconstructions from geological archives in the Ross Sea region by Bella Jane Duncan A thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy In Geology Victoria University of Wellington 2017 Geology! the helicopter rises, the scientists crowd around, and Emily’s drill goes down through a thousand years of ice: ghost of a dog, ghost of a pony Oates going deeper and deeper Below the surface * still perfectly himself still gone for some time, lost in whatever Emily might find of sediments and algae, the movement and retreat of seasons, time passing in samples and traces -beech and conifer- stuff from the core to take home and question and even then perhaps not quite be sure… * May the years of her life look after her Emily’s gone to Antarctica From Hoosh by Bill Manhire i ii Abstract During the Cenozoic Era (the last 65 Ma), Antarctica’s climate has evolved from ice free conditions of the ‘Greenhouse world’, which at its peak (~ 55 Ma) supported near-tropical forests, to the ‘Icehouse’ climate of today with permanent ice sheets, and a very sparse macroflora. This long-term cooling trend is punctuated by a number of major, abrupt, and in some cases, irreversible climate transitions. Reconstructing past changes in vegetation, sea surface temperature, hydroclimate and the carbon cycle require robust geological proxies that in turn can provide insights into climatic thresholds and feedbacks that drove major transitions in the evolution of Antarctica’s ice sheets. Biomarkers allow climate and environmental proxy reconstructions for this region, where other more traditional paleoclimate methods are less suitable. This study has two aims. Firstly to assess the suitability and applicability of biomarkers in Antarctic sediments across a range of depositional settings and ages, and secondly to apply biomarker-based climate proxies to reconstruct environmental and climate conditions during key periods in the development of the Antarctic Ice Sheets. The distribution and abundances of n-alkanes are assessed in Oligocene and Miocene sediments from a terrestrial outcrop locality in the Transantarctic Mountains, and two glaciomarine sediment cores and an ice-distal deep marine core from the western Ross Sea. Comparisons are made with n-alkane distributions in Eocene glacial erratics and sedimentary rocks of the Mesozoic Beacon Supergroup, both likely sources of reworked material. A shift in dominant chain length from n-C29 to n-C27 occurs between the Late Eocene and Early Oligocene, considered a response to a significant climate cooling. Samples from glaciofluvial environments onshore, and subglacial and ice-proximal environments offshore display a reworked n-alkane distribution, characterised by low carbon preference index (CPI), high average chain length (ACL) and high n-C29/n-C27 values. Whereas, samples from lower-energy, more benign lacustrine and ice-distal marine environments predominantly contained contemporary material. Palynomorphs and biomarker proxies based on n-alkanes and glycerol dialkyl glycerol tetraethers (GDGTs) are applied to a Late Oligocene and Early Miocene glaciomarine succession spanning the large transient excursion of the Mi-1 glaciation (~23 Ma) in DSDP Site 270 drill core from the central Ross Sea. While the Late Oligocene is marked by relatively warm conditions, regional cooling initiated a transition into Mi-1. This was likely driven by a combination of decreasing atmospheric CO2 and an orbital geometry favouring low seasonality and cool summers, leading to an intensification of proto-Antarctic bottom water production as iii the Ross Sea deepened and cooled. Mi-1 manifests as a regionally cool period, with minimum subsurface temperatures of ~4°C and onshore mean summer temperatures of ~8°C. A negative n-alkane δ13C excursion of up to 4.8‰ is interpreted as a vegetation response to cold, restricted growing seasons, with plants driven to lower altitudes and more stunted growth forms. However, ocean temperatures remained too warm for marine-based ice sheets to advance onto the outer continental shelf and over-ride the drill site. The large increase in ice volume associated with this event, implied by global δ18O records, was probably held on a higher, terrestrial West Antarctica of greater extent than present day. The relative lack of ice rafted debris during Mi-1, suggests the presence of a marginal marine-terminating ice sheet with fringing ice shelves to the south of DSDP site 270, calving icebergs lacking a basal debris layer, similar to those calving from the Ross Ice Shelf today. This extensive ice cover may explain a large decrease in marine n-alkanes at this time restricting marine productivity on the continental shelf. The biomarker data for the Early Miocene in DSDP 270 indicates a relative warming in both terrestrial and marine temperatures following the transient Mi-1 glacial expansion, but an overall baseline cooling of climate between Late Oligocene and the Early Miocene in the Ross Sea embayment. Isoprenoid GDGTs are used to reconstruct a Cenozoic subsurface ocean temperature compilation L for the Ross Sea, a key source region of ocean deep water. The ocean temperature TEX86 calibration and BAYSPAR in standard subsurface mode were considered, through comparison with independent microfossil and sedimentological data, the most appropriate for use in this region. Ocean temperatures cool prior to the Eocene/Oligocene transition and remain cool for the rest of the Cenozoic, with the exception of short periods of relative warmth in the Late Oligocene and Mid-Miocene Climate Optimum, and long-term trends broadly mirror that of the foraminiferal δ18O record from the deep Pacific. The Δ Ring Index is used to assess non-thermal influences on GDGT distributions, and displays a long term shift from more positive to more negative deviations. This correlates with %GDGT-0, and also relates to a declining trend in the Methane Index, which reflect the contribution of methanogenic and methanotrophic archaea. These changes suggest that these archaea contributed more to the archaeal community in the early to mid Cenozoic, potentially indicating a more anoxic depositional environment in the Ross Sea. The Branched to Isoprenoid Tetraether index (BIT) steadily declines over the Cenozoic, reflecting increasingly hyper-arid conditions onshore, with less active glaciofluvial systems, limited soil development and less ice-free land. iv Acknowledgements This thesis would not have been possible without the support and help of many people. Firstly, thanks must go to my amazing team of supervisors, Rob McKay, James Bendle and Tim Naish. Rob, thanks for giving me the chance to do my ideal PhD project. Your support, encouragement and enthusiasm has made this often stressful process a lot easier. I’m really grateful for all the opportunities you’ve given me over the last few years, including going along to AGU and other conferences, enabling lab visits to Birmingham and taking me along on field trips, even if that’s occasionally involved dealing with some questionable music choices. James, your biomarker knowledge and advice has been invaluable. Thanks for hosting me in Birmingham, teaching me a whole lot about organic geochemistry and for enthusiastic discussions on topics as diverse as compound specific isotope interpretations to possum smiting. Tim, thanks for all your help and advice in setting the stratigraphic scene for my project, and useful discussions on data interpretation and the ‘big picture’. This research would not have been possible without funding support. I’m grateful to Antarctica New Zealand for the Sir Robin Irvine Scholarship and field support in Antarctica. Victoria University of Wellington granted me a Fee’s Waiver and Doctoral Submission Scholarship. I received a SCAR Fellowship which helped cover travel and laboratory costs at the University of Birmingham. I’m grateful for funding received via a Royal Society of New Zealand Rutherford Discovery Fellowship (RDF-13-VUW-003) awarded to Rob McKay. An Antarctic Research Centre Endowed Development Fund grant and SGEES Faculty Strategic Research grant allowed me to travel to Urbino Summer School in Paleoclimatology. Thanks to NERC for funding proposal number BRIS/85/1015, awarded as a grant-in-kind to the Bristol NERC- LSMSF for compound specific GC-ir-MS analyses. I thank the University of Birmingham for support-in-kind (consumables and technical training during laboratory visits). I’m grateful for funding this study received from the MBIE Past Antarctic Climates Program (CO5X1001). Many other people have contributed to this research. Thanks to Richard Levy for your advice, helpful discussions on DSDP 270 and of course for taking me to Antarctica! I thank Todd Ventura for being my local organic geochemistry mentor, running my samples for bulk pyrolysis and for leading the charge on the lab set up. I had a great group helping me in the lab in Birmingham. Heiko Moossen taught me the methods and provided invaluable knowledge. Beth Chamberlain, Carrie Walker and Lucy Tyack were my amazing lab support, both when I was in Birmingham and especially when I was back on the other side of the world. Thanks to v Joe Prebble for processing and counting the palynomorph samples for DSDP 270, and for helpful discussions on interpretation. I’m also grateful to Matt Ryan being a palynomorph diagram whizz so I could make my figures. Denise Kulhanek provided help with the DSDP 270 age model. Thanks to Srinath Krishnan for running my GDGT data and helping me understand it. Thanks to James Super for additional GDGT help and to Mark Pagani for accepting and organising my samples to be run at Yale. I’m grateful to Francesca Sangiorgi, Courtney Warren, Veronica Willmott and Stefan Schouten for willingly providing GDGT data for AND-1B, AND-2A, CIROS-1 and the McMurdo Erratics. Thanks to the Organic Geochemistry Unit at the University of Bristol for analysing my samples for compound specific isotopes.