| Summary: | It is widely accepted that the West Antarctic Ice Sheet (WAIS) was grounded at the continental shelf edge in Eastern Ross Sea during the Last Glacial Maximum (LGM), but the precise chronology is debated. Existing post-LGM ice retreat chronologies are considered suspect because nearly all have been developed using radiocarbon dating of acid-insoluble organics (AIO). Foraminifer tests yield more accurate radiocarbon dates than AIO because unlike loose sediment, foram tests are unlikely to be contaminated by allochthonous carbon, but unfortunately forams are sparse in Antarctic marine sediment cores. Here I utilized a new 3-D multibeam survey of a mid-continental-shelf grounding zone wedge (GZW) and report four consistent radiocarbon dates of forams from four different depth intervals at two core sites on the foreset of the GZW in Eastern Basin, Ross Sea. The forams dated in this study most likely represent a mixture of in situ forams and forams reworked a short distance. These new radiocarbon dates are inconsistent with dates from Western Ross Sea and suggest that the WAIS began retreat across the Ross Sea Eastern Basin prior to 31,000 14C yr BP, more than 10,000 years earlier than previously thought. In the future, if in situ forams can be isolated from foreset sediments within other GZWs, precise dates for grounding event chronologies can be developed, which would ultimately permit us to relate the WAIS retreat to other high-resolution, proxy-based evidence of potential climatic and eustatic forcing.
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