Rapid Thinning of an East Antarctic Outlet Glacier During Stable Holocene Climate

Abstract:

Ice-sheets that are grounded on overdeepened beds below sea-level are potentially vulnerable to collapse. Many outlets of the West Antarctic Ice Sheet that occupy reverse bed slopes are currently in negative mass balance. New ice-penetrating radar data reveal that large overdeepened basins and reverse bed slopes exist under parts of the East Antarctic Ice Sheet, raising concern for its future behaviour. Retreat of the Antarctic ice sheet from the Last Glacial Maximum to its present configuration provides an opportunity to assess ice-sheet response to climate forcing and ice-dynamic feedbacks. Here we report 44 new surface-exposure ages from an East Antarctic outlet glacier that thinned dramatically during the early/mid-Holocene at a rate comparable to modern rates of thinning at Pine Island Glacier. Rapid thinning was coeval with retreat of the grounding-line through an overdeepening on the inner continental-shelf, and the disintegration of a buttressing ice-shelf. We demonstrate that a similar magnitude and timing of ice-dynamic thinning also occurred on the West Antarctic and Peninsula ice-sheets, at a time of relative climatic and oceanic stability after grounding-lines had retreated to the inner continental-shelf. These results imply that significant ice-sheet thinning in the early/mid Holocene arose from topographic feedbacks rather than from significant environmental forcing.