A comparison of supraglacial meltwater features throughout contrasting melt seasons: Southwest Greenland

Abstract. The Greenland Ice Sheet is losing mass through increased melting and solid ice discharge. Supraglacial meltwater features (e.g., lakes, rivers and slush) are becoming more abundant as a result of the former and are implicated as a control on the latter when they drain. It is not yet clear, however, how this system will respond to future climate changes, and it is likely that melting will continue to increase as the Arctic continues to warm. Here, we use Sentinel-2 and Landsat 8 satellite imagery to compare meltwater features in the Russell/Leverett glacier catchment in a high (2019) and a comparatively low (2018) melt year. We find that in the higher melt year: 1) surface meltwater features form and drain, at ~200 and ~400 m higher elevations, respectively, 2) that small lakes (< 0.0495 km²) – typically disregarded in previous studies – are more prevalent and 3) that slush is more widespread. This is important because we show that all three of these sets of features are associated with transient increases in velocity when they drain, and because refreezing of slush can create ice slabs, which inhibit the storage of meltwater in the porous firn and promote surface ponding and runoff in future years. Interestingly, we also identify the potential occurrence of a cascading lake drainage event in the higher melt year, which also appears to perturb ice velocity. Our study therefore suggests that previously poorly mapped and under-studied features (such as small lakes and slush) are actually important in terms of their impact on ice flow and supraglacial runoff, and thus on global sea level rise, in future, warmer, years.