Pleistocene records of ice sheet processes and glacial history from Antarctica and Greenland
Christ, Andrew James
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Anthropogenic climate change is transforming Earth’s Polar Regions. Oceanic and atmospheric warming threaten to melt portions of the Antarctic and Greenland ice sheets and raise sea level dramatically by the end of this century. As a guide for the future, we can examine the geologic record to understand the surface processes that govern ice sheet behavior and establish chronologies of past climate change. In this dissertation, I focus on the Pleistocene glacial history of two polar field sites: the presently ice-free region of McMurdo Sound, Antarctica and formerly glaciated continental shelf of Melville Bugt, Greenland. In my research, I use a combination of detailed geologic mapping, geochemical and isotopic analyses of glacial sediments, and several Quaternary geochronologic techniques. I show that several marine-based ice sheets inundated McMurdo Sound and deposited a series of glacial sediments that record former ice sheet configuration and Antarctic surface processes. Mapping results and a robust radiocarbon chronology indicate that grounded marine-based ice in the Ross Sea overflowed into McMurdo Sound and attained maximum thickness after the global Last Glacial Maximum; ice receded in response to rising sea level and changing ocean circulation. Cosmogenic nuclide exposure ages of boulders from these glacial deposits do not record a simple history of ice extent, but instead the integrated effects of multiple surface processes operating below, along, and above the Antarctic ice sheets. I build upon the insights gained from Antarctica to develop a novel approach to analyzing glacial marine diamict, a mixture of grain sizes and lithologies, deposited on the continental shelf by an expanded Greenland Ice Sheet. Using cosmogenic nuclides, low temperature thermochronometry, and lipid biomarkers, I show that the Greenland Ice Sheet during the Early Pleistocene was similar to today. Extremely low cosmogenic nuclide concentrations indicate the ice sheet already eroded pre-glacial soil cover, but thermochronometry data suggest deep fjords had not yet formed. Abundant lipid biomarkers recovered in this diamict indicate that ice-free areas supported vegetation, similar to the modern ice sheet. This dataset demonstrates how the novel application of proven techniques to glacial sediments can unlock new information about ice sheet history and process.
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