A thicker, rather than thinner, East Antarctic Ice Sheet plateau during the Last Glacial Maximum

Abstract. In this study, we present a surface-exposure chronology of past ice-thickness change derived from in-situ cosmogenic-¹⁴C dating at a site on the edge of the East Antarctic plateau, 380 km inland from the Antarctic coastline. Our knowledge of how the Antarctic ice sheet has responded to Quaternary climate change relies on a combination of geological data and ice-sheet modeling. At the Last Glacial Maximum (LGM), observations and models suggest that increased ice-sheet volume was accommodated by thicker ice near the coast and grounding-line advance towards the continental-shelf edge. In contrast, the ice sheet interior maintained a relatively stable thickness until present, with ice-core evidence even suggesting thinner ice relative to today. However, the magnitude of these thickness changes, and the location dividing thicker versus thinner ice at the LGM is poorly constrained. Geological reconstructions of past ice thickness in Antarctica mostly come from surface-exposure data using cosmogenic nuclides that are relatively insensitive records of ice-cover changes on timescales of tens of thousands of years. This can lead to inaccurate records of LGM ice thickness, particularly towards the East Antarctic plateau, where cold-based non-erosive ice may inhibit bedrock erosion. Samples saturated with ¹⁴C at 1912 m a.s.l. indicate that the summit of Nunatak 1921 was exposed during the LGM, while unsaturated samples indicate that thinning subsequently occurred, with some (25–45 %) post-LGM thinning recorded at ~15–11 ka and most (55–75 %) recorded during the Holocene. These results imply that at least part of the interior East Antarctic Ice Sheet (EAIS) was thicker at the LGM than it is now, and that gradual ice-sheet thinning began ~15 ka. Ice-sheet models that do not account for this thickness change would inaccurately characterize the LGM geometry of the EAIS and underestimate its contributions to deglacial sea-level rise.