A nine-year record of slush on the Greenland Ice Sheet
Journal Article
Overview
abstract
Abstract. Surface melt on the Greenland Ice Sheet has intensified in recent decades, accelerating mass loss. Slush, i.e., water-saturated snow or firn, is a key component of the ice sheet's surface hydrological system, yet its extent and behaviour remain poorly constrained. We present the first classification of slush across the Greenland Ice Sheet, using Sentinel-2 imagery and a random forest classifier to generate a nine-year dataset spanning 2016–2024. Over this period, slush covered a mean seasonal extent of 2.8 % of the ice sheet (∼ 48 100 km2), ranging from 1.1 % (∼ 18 700 km2) in 2018, the lowest-melt year, to 5.1 % (∼ 88 500 km2) in 2019, the highest-melt year. Slush was most extensive in the southwestern and northern basins and most recurrent in the northern and northeastern basins; across these regions, its distribution was associated with bare ice, low-permeability ice slabs and, potentially, finer-scale firn heterogeneity. Slush was the dominant mapped surface meltwater feature by area: in 2019, its extent was nine times the reported combined area of supraglacial lakes, channels, and water-filled crevasses. The mean elevation of the upper slush limit broadly covaried with slush extent, with both increasing during high-melt years. Slush extent and occurrence were associated with higher snowmelt and lower firn air content, while a first-order upper-bound estimate suggests that additional energy absorption associated with slush could produce a mean melt equivalent of 12.4 Gt yr−1 if fully converted to melt. As the ice sheet warms, slush is likely to play an increasingly important role in the surface hydrological system, and its explicit representation in surface energy-balance and hydrological models is required to better constrain future ice-sheet mass-balance projections.
