Collapse of the Last Eurasian Ice Sheet in the North Sea Modulated by Combined Processes of Ice Flow, Surface Melt, and Marine Ice Sheet Instabilities

The record of the confluence and collapse of the British-Irish Ice Sheet and the Fennoscandian Ice Sheet is obscured by the North Sea, hindering reconstructions of the glacial dynamics of this sector of the Eurasian Ice Sheet complex during the last glacial cycle. Previous numerical simulations of the deglaciation of the North Sea have also struggled to capture the confluence and separation of the British-Irish and Fennoscandian Ice Sheets. We ran an ensemble of 70 experiments simulating the deglaciation of the North Sea between 23 and 18 ka BP using the BISICLES ice sheet model. A novel suite of quantitative model-data comparison tools was used to identify plausible simulations of deglaciation that match empirical data for ice flow, margin position, and retreat ages, allowing comparisons to large amounts of empirical data. In ensemble members that best match the empirical data, the North Sea deglaciates through the collapse of the marine-based Norwegian Channel Ice Stream, unzipping the confluence between the British-Irish Ice Sheet and the Fennoscandian Ice Sheet. Thinning of the Norwegian Channel Ice Stream causes surface temperature feedbacks, rapid grounding line retreat, and ice stream acceleration, further driving separation of the British-Irish and the Fennoscandian Ice Sheets. These simulations of the North Sea deglaciation conform with the majority of empirical evidence, and therefore provide physically plausible insights that are consistent with reconstructions based on the empirical evidence, and permit a quantitative comparison between model and data.