West Antarctic ice sheet retreat chronology of two middle-shelf grounding-zone wedges in Eastern Basin, Ross Sea, Antarctica

Abstract

This study isolated a small number of large, in situ and reworked foraminifera from diamicts deposited in two grounding zone wedges on the middle continental shelf in Eastern Basin, Ross Sea, Antarctica. All samples were of sufficient weight to yield Holocene dates if the samples were indeed of Holocene age. Of the twelve small samples sent for radiocarbon analysis, the two heaviest were for reworked foraminifera which yielded dates of >22,200 14C BP and >22,500 14C BP. None of the other ten samples yielded radiocarbon dates. The lack of Holocene radiocarbon dates for the six in situ and four reworked foraminifera samples suggests that West Antarctic Ice Sheet (WAIS) retreated from the middle continental shelf Eastern Basin prior to the Holocene, i.e., much earlier than generally accepted. A second part of this study involved compiling all previous radiocarbon dates from Eastern Basin as well as chronologic information concerning ice-sheet retreat from the surrounding terrestrial areas. This synthesis of marine and terrestrial data suggests that the WAIS retreated from the middle continental shelf at ~26,000 14C BP. The WAIS retreat from the middle continental shelf was not associated with coeval deflation of the ice-sheet surface in the far interior reaches of West Antarctica. Instead, WAIS deflation was delayed by >13,000 years. This delay in the onset of deflation suggests that the effects of ice-sheet retreat from the middle shelf slowly propagated to the interior beginning only after the grounding line had retreated far inland. The retreat of the WAIS from the middle continental shelf towards the interior did ultimately cause deflation beginning first at Siple Dome, ¬¬¬followed by deflation at Reedy Glacier, Marie Byrd Land, and Discovery Ridge as the grounding line migrated to its present-day position.