Sedimentary Signature of Past Ice Sheet and Ocean Dynamics in Antarctica

The Antarctic Ice Sheet is currently losing mass, in part owing to extensive regions of ice grounded below sea level that are vulnerable to instability and rapid retreat. Reconstructions of past dynamics and extent of the Antarctic Ice Sheet provide an important context for understanding controls on ice-sheet behavior and are required to accurately predict the future behavior of ice sheets and global sea-level changes during a warming climate. This work investigated the sedimentological record recovered from two regions of the Antarctic margin to reconstruct ice-sheet history and to provide constraints for understanding past glacial dynamics. We used sediment characteristics as a tool to constrain paleo-depositional environments down-core in relation to ice sheet extent and glacial cycles. Micro- to macro-scale analyses were conducted to examine subglacial and marine sediments from the Ross Sea and Amundsen Sea region, respectively. Deposits from the Last Glacial Maximum in the western Ross Sea provide an opportunity to investigate paleo-ice stream processes using sediment cores associated with glacial landforms. We observed variations in sediment properties within subglacial deposits that suggests different sediment response to glacial stress, resulting in non-pervasive deformation within the till. These observations are consistent with the interpretation that a dynamic ice sheet with variable flow regimes existed across the Ross Sea during the Last Glacial Maximum. International Ocean Discovery Program Expedition 379 obtained drill core records from the Amundsen Sea continental rise, to document West Antarctic Ice Sheet history in a region currently experiencing the largest ice loss in Antarctica. Detailed facies investigations were conducted on Late Miocene to Pliocene strata and established sedimentary facies associated with interglacial and glacial periods. Massive, bioturbated muds with clasts were deposited through bottom current and hemipelagic processes during interglacial periods, while laminated silty clay intervals dominated by terrigenous components were supplied by downslope transport during glacial periods. The contacts observed at the top of the interglacial deposits to the onset of glacial periods are sharp. We interpret the sudden transition from interglacial to glacial facies to indicate West Antarctic Ice Sheet did not fully collapse during Late Miocene-Pliocene interglacial periods, which allowed rapid onset of glacial periods that initiated downslope gravity transport. Despite no indication of collapse, our records show evidence for extended warm periods with polythermal ice sheets capable of extensive subglacial deformation and erosion, likely contributing to the overdeepened topography of the continental shelf.