Comparing the Simulated Surface Mass Balance of the Laurentide Ice Sheet During the Last Deglaciation With a Geophysical Reconstruction

Abstract

Despite decades of research, our understanding of the role of climate feedbacks in shaping Pleistocene glacial cycles remains incomplete. Here, we investigate the decay of the Laurentide Ice Sheet (LIS) by calculating its surface mass balance (SMB) during the last deglaciation using the isotope‐enabled transient climate model experiment (iTraCE). To do this, we compare two frameworks for calculating the melt rate, employ a parameterization of the refreezing of snow melt and liquid precipitation, and apply statistical downscaling. We compare the SMB to the ice mass rate of change deduced from the ICE‐6G reconstruction from Last Glacial Maximum (LGM; ∼21 ka) until 12 ka. We find that the SMB derived from iTraCE overestimates mass loss from 20 to 18 ka (corresponding to an approximately 60% excess in cumulative mass loss) and more closely aligns with the ICE‐6G after 18 ka. A key finding is that meltwater forcing plays a critical role in shaping SMB evolution. Its inclusion produces abrupt shifts in SMB and improves agreement with ICE‐6G during Heinrich Stadial 1 and the Younger Dryas, highlighting the importance of ocean circulation and sea ice feedbacks in modulating melt rates. During the Bølling–Allerød, strongly negative SMB is consistent with mass loss in ICE‐6G, but dynamic ice loss is required, perhaps triggered by surface melt. These results demonstrate that SMB derived from transient climate simulations can reproduce key features of deglacial ice sheet evolution when meltwater forcing is appropriately included, and underscore the importance of coupled surface and dynamic processes in shaping ice sheet evolution.