Proglacial lakes substantially modulate the surface mass balance of deglacial ice sheets

Abstract. During the last deglaciation large proglacial lakes formed at the base of retreating ice sheets, retaining a cold surface during summer due to iceberg calving and meltwater inflow. Here we assess the climate effect of proglacial lakes on the surface mass balance of the nearby Laurentide (LIS) and Fennoscandian (FIS) ice sheets. Using an atmospheric model with a new extension for proglacial lakes and an ice sheet surface mass balance scheme we conduct a set of simulations inspired by the Allerød interstadial around 13000 years before present. We demonstrate that the presence of proglacial lakes significantly reduces summer air temperatures in a larger area around the proglacial lakes and leads to reduced precipitation with increased snow/rain ratio. The climatic effect is further amplified when lake temperatures are constrained to remain below 4 °C throughout the year to account for cooling from meltwater and ice entering the lake. In our experiments total melt reduces by 18 % and 27 % for the LIS and FIS respectively due to the presence of lakes, and by 23 % and 35 % if the same lakes are additionally cooled. The climate response to the existence of proglacial lakes may thus be an important opponent to positive dynamical feedback during deglacial periods with rapid retreat of continental ice sheet margins and proglacial lake formation.