Minimal Impact of Late-Season Melt Events on Greenland Ice Sheet Annual Motion

Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. In this study we investigate the impact of these large late-season melt events on the ice dynamics of five land- and two marine-terminating outlet glaciers of the west Greenland Ice Sheet. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ~240% relative to pre-event velocities. However, ice velocity returned rapidly to pre-event levels, and the speed-ups caused a regional increase in annual ice discharge of only ~2% compared to when the effects of the speed-ups on ice discharge were excluded. In contrast, the total annual runoff from the studied glaciers increased by 24%. Therefore, although late-season melt events are forecast to become more frequent and drive large amounts of runoff, their impact on net mass loss via ice discharge is minimal.