Marine ice sheet instability and ice shelf buttressing of the Minch Ice Stream, northwest Scotland

摘要

Uncertaintiesin future sea level projections are dominated by our limited understanding ofthe dynamical processes that control instabilities of marine ice sheets. Thelast deglaciation of the British–Irish Ice Sheet offers a valuable exampleto examine these processes. The Minch Ice Stream, which drained a largeproportion of ice from the northwest sector of the British–Irish Ice Sheetduring the last deglaciation, is constrained with abundant empirical datawhich can be used to inform, validate, and analyse numerical ice sheetsimulations. We use BISICLES, a higher-order ice sheet model, to examine thedynamical processes that controlled the retreat of the Minch Ice Stream. Weperform simplified experiments of the retreat of this ice stream under anidealised climate forcing to isolate the effect of marine ice sheetprocesses, simulating retreat from the continental shelf under constant“warm” surface mass balance and sub-ice-shelf melt. The model simulates aslowdown of retreat as the ice stream becomes laterally confined at the mouthof the Minch strait between mainland Scotland and the Isle of Lewis,resulting in a marine setting similar to many large tidewater glaciers inGreenland and Antarctica. At this stage of the simulation, the presence of anice shelf becomes a more important control on grounded ice volume, providingbuttressing to upstream ice. Subsequently, the presence of a reverse slopeinside the Minch strait produces an acceleration in retreat, leading to a“collapsed” state, even when the climate returns to the initial “cold”conditions. Our simulations demonstrate the importance of the marine icesheet instability and ice shelf buttressing during the deglaciation of partsof the British–Irish Ice Sheet. We conclude that geological data could beapplied to further constrain these processes in ice sheet models used forprojecting the future of contemporary ice sheets.