Deglacial Ice Sheet Instabilities Induced By Proglacial Lakes

During the last deglaciation (21-7 kaBP), the gradual retreat of Northern Hemisphere ice sheet margins produced large proglacial lakes. While the climatic impacts of these lakes have been widely acknowledged, their role on ice sheet grounding line dynamics has received very little attention so far. Here, we show that proglacial lakes had dramatic implications for the North American ice sheet dynamics through a self-sustained mechanical instability which has similarities with the known marine ice sheet instability consequently providing fast retreat of large portions of the ice sheet over the continent. This instability mechanism is likely important in contributing to deglaciation of terrestrial glaciers and ice sheets with proglacial lakes at their margins as it can substantially accelerate the mass loss. Echoing our knowledge of Antarctic ice sheet dynamics, proglacial lakes are another manifestation of the importance of grounding line dynamics for ice sheet evolution.Plain Language Summary The last deglaciation provides a unique opportunity to understand the mechanisms behind large-scale ice sheet collapses. However, the mass loss accelerations that occurred during the deglaciation remain only partially explained despite recent improvements of ice sheet models which now better represent ice dynamics than they used to. Here we use such a model to quantify for the first time the importance of proglacial lakes on the dynamics of the North American ice sheet during the last deglaciation. We show that these lakes could be responsible for large-scale ice sheet collapses due to a floatation instability. The proglacial lake ice sheet instability could be an additional mechanism explaining the rapid ice sheet retreat during the deglaciation.Key PointsThe North American proglacial lakes induce an ice sheet instability during the last deglaciation.This instability is mechanically driven even though it is triggered by surface mass balance.The instability could explain half of the mass loss when the ice sheet reaches the region of the present-day Hudson Bay.