The role of ocean forcing in early deglaciation of the British-Irish Ice Sheet during the Last Glacial Maximum: A micropalaeontological and sedimentological study of sediment cores from the Malin Sea and Slyne Trough

The contribution of the polar ice sheets to global sea level rise has tripled within the last two decades, and remains the largest yet most uncertain source of future sea level rise. Critical to this problem are the sensitive marine-terminating margins of ice sheets, which can propagate marine-forced changes into the ice-sheet interior but whose responses remain insufficiently understood and challenging to simulate. Improving our understanding of ice sheet-ocean interactions is therefore an essential prerequisite to accurate projections of future sea level rise. Geological records of ice sheet-ocean interaction are valuable to this effort, as they can span centennial to millennial timescales, providing longer-term context to instrumental observations and important means of informing and testing numerical ice-sheet models used in predictions of sea-level rise. The last British-Irish Ice Sheet (BIIS) has important potential in this regard, due to its largely marine-based configuration and proximity to pathways of poleward heat transport in the northeast Atlantic. This study avails of this by investigating whether ocean forcing played a role in early deglaciation in two sectors along the Atlantic margin of the BIIS, the Malin shelf and Porcupine Bank-Slyne Trough region, using foraminiferal assemblages. The results suggest that warm Atlantic Water was present during early deglaciation (from ≥25.5 ka BP) in the Porcupine Bank-Slyne Trough region, and passively drove retreat offshore central western Ireland. In contrast, deglaciation on the Malin shelf occurred in a cold glacimarine environment from ≥25.9 ka BP and was likely internally-driven through glacioisostatic adjustment-induced relative sea-level rise, consistent with recent results from two other sectors along the BIIS’s Atlantic margin. The findings expose the role of bathymetry in locally conditioning the BIIS to ocean forcing, and imply a BIIS influence by Atlantic Water advection in the northeast Atlantic during the coldest stadials of the last glacial period.