The Presence and Widespread Distribution of Dark Sediment in Greenland Ice Sheet Supraglacial Streams Implies Substantial Impact of Microbial Communities on Sediment Deposition and Albedo

Abstract

AbstractMelting on the Greenland Ice Sheet leads to extensive supraglacial stream networks. These streams accumulate low‐albedo sediments disproportionately contribute to melting. Studies analyzing supraglacial sediment distribution and hydrodynamic properties are rare. Here, we examine a 130‐m supraglacial stream reach in southwest Greenland using drone imagery, bathymetry, and hydrology measurements from 2017. Sediment covered 24% of the channel and had a mass‐median diameter of 0.027 mm. We applied calculations of critical Shields stress to determine the minimum water depth needed to initiate sediment movement. In order for theoretical critical water depths to match observed depths, sediment grains would need to be 2.48 mm (near the grain size for cryoconite granules) indicating that microbial growth within sediment caused extensive flocculation. Without flocculation, sediment would flush out of floodplains and supraglacial streams would have significantly higher albedos. Supraglacial stream albedo might therefore be sensitive to changing stream chemistry, temperature, and meltwater supply.