Growth and retreat of the West Antarctic Ice Sheet from the last glacial maximum to the present in the eastern Ross Sea, Antarctica
Mosola, Amanda Beth
Anderson, John B.
Doctor of Philosophy
Marine geological evidence supports rapid retreat of the West Antarctic Ice Sheet in the eastern Ross Sea before the last glacial maximum. As the only accessible marine record of a major drainage outlet of the West Antarctic Ice Sheet (WAIS), this central and eastern Ross Sea dataset provides a unique opportunity to test the hypothesis of WAIS instability, assess its regulating role in eustasy, and explore the geological record of paleo-ice stream behavior. As the last vast marine-based ice sheet on the planet, the WAIS is seen as a key source of potentially rapid sea level rise. The collapse and disintegration of the WAIS would raise sea level by 5--6 m, a major threat to the world's coastal cities. Marine geological data were collected along the axis of large bathymetric troughs during a 1999 cruise of the R/V Nathanial B. Palmer. Thick till sheets, extensive lineations, and multiple grounding zone wedges imaged on seismic profiles and multibeam bathymetric records, indicate that troughs in the Ross Sea were occupied by paleo-ice streams during the last glacial maximum. Ice stream boundaries in the eastern Ross Sea are characterized by laterally accreting sedimentary strata indicating lateral migration of ice streams. The abrupt transition from lineated to non-lineated morphologies reflects sharp ice stream margins. Sediment cores recovered glacial-marine deposits overlying till, a facies succession that indicates an abrupt transition from subglacial to open marine deposition. High concentrations of ice rafted debris in the glacial-marine units and iceberg furrows suggest mass wasting of the ice sheet and iceberg calving from the grounding line during retreat. Corrected radiocarbon ages of samples taken above the contact between subglacial (till) and glacial-marine sediments range from 23.4 to 26.0 ka. B.P., indicating pre-LGM ice sheet withdrawal in the eastern Ross Sea. This was long before the ice sheet retreated from the western Ross Sea and is inconsistent with previous models for ice sheet retreat in the region.