Contrasting modes of deglaciation between fjords and inter-fjord areas in eastern North Greenland

Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer-term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new(10)Be surface exposure ages combined with existing minimum-limiting(14)C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems - Independence Fjord, Hagen Fjord and Danmark Fjord. The(10)Be ages are generally scattered and many of the samples are significantly older than expected, with pre-LGMages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new(10)Be ages and existing(14)C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between similar to 11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land-based in the central and southern part of the study area where the ice margin first reached its present extent by similar to 6.7 ka. As the onset of Neoglacial ice advance had already commenced at similar to 5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30-40 km of its present extent. The contrasting behaviour between the fjords and inter-fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrISmay respond to a warmer climate in various topographic settings and may provide useful constraints for future ice-sheet models.