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Ice Dynamics of the Darwin-Hatherton Glacial System, Transantarctic Mountains, Antarctica

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Ice Dynamics of the Darwin-Hatherton Glacial System, Transantarctic Mountains, Antarctica Ice dynamics of the Darwin-Hatherton glacial system, Transantarctic Mountains, Antarctica A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geography By Mette Riger-Kusk University of Canterbury 2011 i Abstract The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and through the Transantarctic Mountains (TAM) before entering the Ross Embayment. Large ice-free areas covered in glacial sediments surround the DHGS, and at least five glacial drift sheets mark the limits of previous ice extent. The glacier belongs to a group of slow-moving EAIS outlet glaciers which are poorly understood. Despite this, an extrapolation of a glacial drift sheet boundary has been used to determine the thickness of the EAIS and the advanced West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM). In order to accurately determine the past and present contributions of the Antarctic ice sheets to sea level changes, these uncertainties should be reduced. This study aims to examine the present and LGM ice dynamics of the DHGS by combining newly acquired field measurements with a 3-D numerical ice sheet-shelf model. The fieldwork included a ground penetrating radar survey of ice thickness and surface velocity measurements by GPS. In addition, an extensive dataset of airborne radar measurements and meteorological recordings from automatic weather stations were made available. The model setup involved nesting a high-resolution (1 km) model of the DHGS within a lower resolution (20 km) all-Antarctic simulation. The nested 3-D modelling procedure enables an examination of the impact of changes of the EAIS and WAIS on the DHGS behaviour, and accounts for a complex glacier morphology and surface mass balance within the glacial system. The findings of this study illustrate the difference in ice dynamics between the Darwin and Hatherton Glaciers. The Darwin Glacier is up to 1500 m thick, partially warm-based, has high driving stresses (~150 kPa), and measured ice velocities increase from 20-30 m yr-1 in the upper parts to ~180 m yr-1 in the lowermost steepest regions, where modelled flow velocities peak at 330 m yr-1. In comparison, the Hatherton Glacier is relatively thin (<900 m), completely cold-based, has low driving stresses (~85 kPa), and is likely to flow with velocities <10 m yr-1 in most regions. It is inferred that the slow velocities with which the DHGS flows are a result of high subglacial mountains restricting ice flow from the EAIS, large regions of frozen basal conditions, low SMB and undulating bedrock topography. The model simulation of LGM ice conditions within the DHGS implies that the ice thickness of the WAIS has been significantly overestimated in previous reconstructions. Results show that the surface of the WAIS and EAIS away from the TAM would have been elevated 600-750 and 0-80 m above present-day levels, respectively, for the DHGS to reach what was inferred to represent the LGM drift sheet limit. Ultimately, this research contributes towards a better understanding of the dynamic behaviour of slow moving TAM outlet glaciers, and provides new insight into past changes of the EAIS and WAIS. This will facilitate more accurate quantifications of contributions of the WAIS and EAIS to changes in global sea level. ii Acknowledgements This has been a long journey, which has taken me to one of the most remarkable places on the planet, and I would like to thank all of the people that have helped me on my way. First of all, a big thank you to my three supervisors Wendy Lawson, Wolfgang Rack and Brian Anderson. You have all helped me move forward when I most needed it, and I especially enjoyed the discussion and stories shared during dinner in a small yellow tent. During my studies I have had had the privilege of working alongside helpful and enthusiastic people in the Department of Geography and Gateway Antarctica, some of whom I will mention here. Bryan Storey introduced me to the Antarctic environment for which I will always be grateful. Peyman Zawar-Reza inspired me about meteorological datasets and Ian Owens, with his wealth of knowledge, offered timely and important advice. I would also like to thank Irfon Jones who taught me about cartography with patience and humour, Justin Harrison and Nick Key who helped organise and plan my fieldwork, Marney Brosnan who twice ‘volunteered’ for the ungrateful task of designing my posters while I was away, and Graham Furniss and Steven Sykes who made the modelling part of this work possible with their knowledge of computers and programming. I would also like to acknowledge the expertise and help offered by people from outside the department. In particularly, I would like to thank David Pollard for allowing me to use his model in my work and for providing invaluable advice along the way, and Donald D. Blankenship and his team for adjusting their ICECAP field campaign to include airborne radar measurements over the DHGS and letting me use these in my work. I am also grateful for the advice on GPR processing and interpretation offered by Mike Finnemore, Matt Nolan and David Nobes, which significantly improved this part of my work. Thank you also to Dean Arthur for his great company and ability to keep us safe during the fieldwork. Also of importance to this work is the SPIRIT DEM which was made available through the project IPY ASAID (Co-PI: W. Rack). Without the financial and logistical support of Antarctic New Zealand, none of this could have been possible, and I thank the staff in Christchurch and at Scott Base for an enjoyable working relationship. Education New Zealand has supported me throughout this research with a New Zealand International Doctoral Research Scholarship, and my participation in a course in Italy was financed by the Department of Geography and Gateway Antarctica. Finally, I would like to thank my family and friends at home and in New Zealand, who have supported me with humour and love in whatever adventure I have embarked upon. I especially thank Mark, who despite these last crazy months, still plans to marry me this autumn. iii Contents Abstract ....................................................................................................... ii Acknowledgements ......................................................................................iii List of tables .............................................................................................. viii List of figures ............................................................................................... ix List of abbreviations .................................................................................... xii 1 Introduction ........................................................................................... 1 1.1 Aims and objectives .................................................................................... 2 1.2 General characteristics of the WAIS and EAIS ................................................ 5 1.3 Current mass balance of the WAIS and EAIS ................................................. 6 1.4 Changes in the WAIS and EAIS since the LGM ................................................ 7 1.4.1 Changes in the WAIS during and since the LGM .................................... 8 1.4.2 Changes in the EAIS during and since the LGM ................................... 10 1.5 Glaciers in the Transantarctic Mountains ..................................................... 10 1.5.1 Mass balance ................................................................................. 11 1.5.2 Characteristics of fast moving outlet glaciers ...................................... 13 1.5.3 Characteristics of slow moving outlet glaciers ..................................... 16 1.6 Change of glaciers in the Transantarctic Mountains since the LGM .................. 18 1.7 Thesis outline .......................................................................................... 19 1.8 Summary ................................................................................................ 21 2 Introduction to the Darwin-Hatherton glacial system ........................... 22 2.1 Regional setting ....................................................................................... 24 2.2 Surface topography .................................................................................. 25 2.3 Climate and surface mass balance .............................................................. 26 2.4 Ice surface features .................................................................................. 27 2.5 Ice thickness ........................................................................................... 29 2.6 Ice velocity .............................................................................................. 30 2.7 Grounding line position ............................................................................. 31 iv 2.8 Basal properties ....................................................................................... 31 2.9 Geomorphology and glacial history ............................................................. 32 2.9.1 Glacial drift sheets .......................................................................... 33 2.9.2 Glacial history of the DHGS .............................................................. 34 2.9.3 Evidence from the DHGS on past changes of the Antarctic Ice Sheet ..... 36 2.10 Summary ..............................................................................................
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