A North Greenland-wide in situ cosmogenic 14C ice sheet chronology since the Lateglacial

Abstract

Knowledge of the glacial history of the North Greenland Ice Sheet is crucial due to its high sensitivity to climate change. However, because the ice sheet in this region is predominantly cold-based, resulting in low erosion rates, using 10Be exposure dating to establish reliable ice sheet chronologies has proven very challenging due to nuclide inheritance. In this study, we measure 16 rock samples for their in situ 14C concentration, most of which already showed 10Be nuclide inheritance, resulting in apparent exposure ages pre-dating the most recent deglaciation. We combine our new results with seven already published in situ 14C exposure ages to build a North Greenland-wide in situ 14C ice sheet chronology based on a total of 20 boulder and three bedrock samples. Resulting in situ 14C ages range from 4.8 to 22.4 ka, and more than half of our in situ 14C exposure ages show signs of excess nuclides, pre-dating the most recent deglaciation at individual sample sites. We believe the excess nuclides could be a result of limited erosion during the Last Glacial Maximum (LGM) and a combination of pre-LGM exposure, supraglacial pre-deposition exposure and possibly thin ice cover. Our new large-scale in situ 14C data set contributes important knowledge on the glacial history of North Greenland and ice-bed properties in this region. Despite challenges, all in situ 14C exposure ages except two are younger than their 10Be counterpart, which highlights the potential and necessity of in situ 14C exposure dating in regions with cold-based ice and low erosion rates.