Today, Antarctica is covered by an ice sheet that, if it were to melt, has the capacity to contribute on the order of nearly 60 meters to global sea-level rise. Most of that ice is stable and is expected to be so long into the future, but parts of the West Antarctic Ice Sheet, particularly Thwaites and Pine Island glaciers, are susceptible to sudden retreat, or even “collapse.” In the past, the ice was significantly expanded, reaching the continental shelf break around most of the margin. As the ice sheet retreated to its modern extent, the shrinking ice left behind a sedimentary signature of deglacial history. Over repeated cycles of glacial advance and retreat, in some places at least since the latest Eocene, sedimentary deposits of alternating glacial and interglacial periods have built up on the continental shelf and slope. Because the stability of the Antarctic Ice Sheet is strongly influenced by the ocean, the sedimentary deposits from the ice-ocean margin are the ideal place to study the controls on stability or instability of the ice.

This talk will focus on using the sedimentary record from the West Antarctic margin, by combining geophysical survey data, including 3.5 kHz profiles, seismic data, and multibeam swath bathymetry, with both gravity and drill cores, to map the past extent of the ice, determine the chronology of glacial cycles, and estimate the controls on glacial stability. Data will be presented from three different time periods. First, we will review data from deep-water sites, beyond the glacial limit and thus not susceptible to erosion, where drill cores have recovered continuous records of glacial cyclicity since the Neogene, allowing correlation to global sea-level records. Next, we will examine records of retreat since the last glacial maximum, at the end of the Pleistocene, where the difference in timing of retreat in individual drainage basins can be determined. Finally, we will look at the sedimentary records from where Thwaites Glacier has retreated over just recent decades, allowing an examination the factors influencing the ice today and how they differ from past periods.