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 not well constrained due to limited stratigraphic control, lack of geological deposits, and inconclusive dates. For the Greenland Ice Sheet (GrIS), it is generally assumed that the ice extended beyond the present-day coast during MIS 3, although some data suggest that it might have had a more limited ice extent. In this study, we constrain the timing and extent of the west and northwest GrIS by modelling the inherited signal from the nuclide inventory of in situ ¹⁴C and ¹⁰Be. Our results show that the coastal areas of west and northwest Greenland were ice-covered during MIS 4, followed by a ~20 ka long period where the ice margin was located near the current ice margin before the Last Glacial Maximum (LGM). We furthermore find that the pre-LGM exposure must have occurred towards the end of MIS 3 to be captured by the in situ ¹⁴C signal. Finally, we find that the LGM advance likely began late and only exceeded the present coastline after 20 ka. Our results show that modelling the inherited in situ ¹⁴C and ¹⁰Be signals provides a new way to constrain MIS 4–2 ice fluctuations of Northern Hemisphere ice sheets.