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, seasonally unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to similar to 240% relative to pre-event velocities. However, ice motion returned rapidly to pre-event levels, and the speed-ups caused a regional increase in annual ice discharge of only similar to 2% compared to when the effects of the speed-ups were excluded. Therefore, although late melt-season events are forecast to become more frequent and drive significant runoff, their impact on net mass loss via ice discharge is minimal. Extreme melt and rainfall events can cause the flow of ice on the Greenland Ice Sheet to accelerate, potentially causing more ice to move to lower elevations, where temperatures are warmer and melt rates are higher. In September 2022, there were multiple unprecedented melt events. Their intensity caused some glaciers on the ice sheet to speed up by 240% relative to pre-event speeds. Despite these accelerations, our analyses show that these events had only a minimal long-term impact on how much ice was moved to lower elevations due to the short duration of the speed-ups. As a result, while these melt-induced speed-ups are expected to become more common in a warmer climate, their effect on the amount of ice transported toward the ice margins is minimal. September 2022 saw multiple melt events over the west Greenland Ice Sheet, with the largest daily runoff of any late melt-season since 1950 Large quantities of surface-generated meltwater overwhelmed the subglacial drainage system causing brief increases in ice velocity Late-season runoff-induced speed-ups have only minimal impact on the mass balance of the Greenland Ice Sheet via dynamical processes