UC Santa Cruz

With more than 70m of sea level equivalent ice stored in the polar ice sheets, sea level forecasting is heavily reliant on projections of ice sheet response to changes in global climate. One way that Earth scientists have approached this problem is to look back at past warm periods to determine how terrestrial ice mass changed in during previous climatic events. In Antarctic, however, there is an added complexity that 97.6% of the modern continent is covered by ice, which restricts access to the geologic record. Without terrestrial archives of Antarctic ice sheet evolution, it is challenging to parameterize the dominant processes that govern ice sheet sensitivity to climate and the environmental effects of ice loss. In this dissertation, I applied geochronologic, isotopic, elemental, and spectroscopic analyses to Antarctic subglacial chemical precipitates – a novel terrestrial record of basal conditions – to investigate the processes that link climate change, Antarctic ice motion, and the hydrologic system at the ice-bed interface. Collectively, this work expands our understanding of Antarctic evolution on centennial to millennial timescales and establishes Antarctic subglacial precipitates as climate archives analogous to speleothems.The first two chapters investigate the physical processes associated with subglacial hydrology and ice motion. By applying geochronologic and geochemical analyses to a group of precipitates that formed over tens-of-thousands of years during the Late Pleistocene, we showed that the continent-wide Antarctic subglacial hydrologic system responds rapidly (within 60 yrs.) to millennial-scale climate events, with more intense subglacial flushing during warm periods and diminished basal meltwater flow during cold periods. This close coupling between climate and subglacial hydrologic activity requires changes to Antarctic ice surface slope caused by hundreds of meters of thinning at the ice sheet margins. These studies provide evidence that the Antarctic gains and loses ice during millennial-scale climate cycles and indicate that subglacial meltwater flushing drive higher ice velocities that promote ice thinning and grounding line retreat. The latter chapters focus on the mechanisms that control the chemical composition of subglacial waters, to help discern the environmental effects of Antarctic ice loss on geologic timescales. The third chapter uses stable isotope measurements ( carbon and oxygen) on a suite of 49 subglacial precipitates to show that microbial activity mobilizes fossil carbon stored in rocks and sediment throughout the Antarctic continent. This respired CO2 drives a continent-wide silicate weathering cycle that mobilizes elements from the subglacial bedrock, which may play an important role in fertilizing the Southern Ocean ecosystem. Chapter 4 established 10 kyr record of trace metal cycling beneath the East Antarctic Ice Sheet (EAIS) measured in a subglacial precipitate that formed across glacial termination III. This record implies that climate modulated changes in subglacial flushing intensity regulate the mobilization of redox sensitive trace metals on geologic timescales.