Sediment plumes as a proxy for local ice-sheet runoff in

ABSTRACT. Meltwater runoff is an important component of the mass balance of the Greenland ice sheet (GrIS) and contributes to eustatic sea-level rise. In situ measurements of river runoff at the!325 outlets are nonexistent due to logistical difficulties. We develop a novel methodology using satellite observations of sediment plumes as a proxy for the onset, duration and volume of meltwater runoff from a basin of the GrIS. Sediment plumes integrate numerous poorly constrained processes, including meltwater refreezing and supra- and englacial water storage, and are formed by meltwater that exits the GrIS and enters the ocean. Plume characteristics are measured in Moderate Resolution Imaging Spectroradiometer (MODIS, band 1, 250m) satellite imagery during the 2001–08 melt seasons. Plume formation and cessation in Kangerlussuaq Fjord, West Greenland, are positively correlated (r2 = 0.88, n=5, p<0.05; r2 = 0.93, n=5, p<0.05) with ablation onset and cessation at the Kangerlussuaq Transect automatic weather station S5 (490ma.s.l., 6 km from the ice margin). Plume length is positively correlated (r2 = 0.52, n=35, p<0.05) with observed 4 day mean Watson River discharge throughout the 2007 and 2008 melt seasons. Plume length is used to infer instantaneous and annual cumulative Watson River discharge between 2001 and 2008. Reconstructed cumulative discharge values overestimate observed cumulative discharge values for 2007 and 2008 by 15 % and 29%, respectively