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Abstract Ice-sheet volume during Marine Isotope Stage (MIS) 3 (57–29 ka) is controversial. Several recent studies have proposed that the Greenland Ice Sheet was smaller during MIS 3 than it is today based on radiocarbon ages of molluscan bivalve shells reworked into sedimentary deposits adjacent to the present ice margin. Such a result contrasts with available records of MIS 3 climate, ice volume, and sea level. We revisited a site previously interpreted as containing evidence for smaller than present ice during MIS 3. We collected marine bivalve shells and combined progressive acid dissolution in preparation for radiocarbon dating with new-generation amino acid analysis, which focuses on aspartic acid racemization. Our results suggest that contamination by young carbon yields finite radiocarbon ages despite bivalve shells likely dating to MIS 5e (∼125 ka) or even older. This result should be further tested, which could be accomplished with additional studies of this kind in combination with ice-sheet modeling and additional paleoclimate data generated from adjacent seas. 

The persistence and size of the Greenland Ice Sheet (GrIS) through the Pleistocene is uncertain. This is important because reconstructing changes in the GrIS determines its contribution to sea level rise during prior warm climate periods and informs future projections. To understand better the history of Greenland’s ice, we analyzed glacial till collected in 1993 from below 3 km of ice at Summit, Greenland. The till contains plant fragments, wood, insect parts, fungi, and cosmogenic nuclides showing that the bed of the GrIS at Summit is a long-lived, stable land surface preserving a record of deposition, exposure, and interglacial ecosystems. Knowing that central Greenland was tundra-covered during the Pleistocene informs the understanding of Arctic biosphere response to deglaciation.