Evidence of a reduced Greenland Ice Sheet during Marine Isotope Stage 3 based on modelling of in situ 14C and 10Be nuclides

The extent of the Northern Hemisphere ice sheets during Marine Isotope Stage 3 (MIS 3, 57-29 ka) is generally poorly constrained due to limited stratigraphic control, a lack of geological deposits, and inconclusive dates. For the Greenland Ice Sheet (GrIS), it is typically assumed that the ice extended beyond the present-day coast during MIS 3, although some data suggest a more limited ice extent. In this study, we constrain the timing and extent of the west and northwest GrIS by modelling the inherited in situ 14 C and 10 Be signal in bedrock samples using a novel modelling framework called CEDIS (Cosmogenic Exposure Dating with Inherited Signals). Our results show that the coastal areas of West and Northwest Greenland were ice-covered during MIS 4 (71-57 ka). This was followed by a ∼20 ka long period that preceded the Last Glacial Maximum (LGM) during which the ice margin most likely was located near the current margin. We find that the pre-LGM exposure must have occurred towards the end of MIS 3 to be captured by the in situ 14 C signal. Our model results further indicate that the LGM advance likely began late and only exceeded the present coastline after 20 ka, which is later than the widely accepted global LGM period (26-19 ka). Moreover, the amount of subglacial erosion must have been negligible, as any subglacial erosion would render the local LGM estimates even younger. Overall, our results indicate an unusually late local LGM at the western and northwestern coast of Greenland, and that these sectors of the GrIS were more dynamic than hitherto believed. They also show that modelling the inherited in situ 14 C and 10 Be signals in bedrock provides a viable approach to constrain MIS 4–2 ice fluctuations of glaciers and ice sheets.