Widespread lake-terminating glacier slowdown despite ice-marginal lake expansion in Greenland

Accelerated global warming is driving significant mass loss from the Greenland Ice Sheet (GrIS), leading to widespread ice-margin retreat and increased meltwater runoff. Both processes have resulted in a widespread increase in the number, area, and volume of ice-marginal lakes. These proglacial water bodies are known to possess significant potential to influence ice motion and, thus, ice sheet stability by altering thermal and mechanical boundary conditions at the terminus. Consequently, there is an imperative to understand how recent expansions in lake extent have impacted ice dynamics around the margins of the GrIS.

In this study, we investigate changes in near-terminus ice dynamics for the 76 glaciers draining into the 70 largest ice-marginal lakes around the GrIS over a 25-year period (1999–2024). We analyze velocity variation within the near-terminus region to isolate the direct influence of the ice-marginal lake. The results show that the studied glaciers have experienced an overall slowdown in ice motion of 19% between 1999 and 2024. While we observe regional variability across the ice sheet, no individual sector exhibits aggregate acceleration. Overall, only 32% of the studied glaciers accelerated in their near-terminus region. In these specific instances, speed-up is driven primarily by ice-marginal thinning and/or proglacial lake deepening, both of which increase flotation and consequently reduce basal drag.

These findings challenge the prevailing view that ice-marginal lake growth inevitably promotes dynamic instability. While ice-marginal lakes are increasing around the GrIS, we find no evidence over the last 25 years that these systems are making an increasing contribution to ice mass loss via ice dynamics. This suggests that many ice-marginal lakes lack the depth or overdeepened bed topography necessary to induce significant flotation-driven instability.