Surface meltwater runoff routing through a coupled supraglacial-proglacial drainage system, Inglefield Land, northwest Greenland

Abstract

The northwest Greenland Ice Sheet (NW GrIS) is rapidly losing mass, and its ablation zone has expanded over the past two decades. Numerous supraglacial streams flowing directly over the NW GrIS surface drain a large lobe of grounded ice at Inglefield Land, into the proglacial Minturn River and the Nares Strait. Owing to the absence of moulins and crevasses, this continuous supraglacial-proglacial drainage system regulates the evacuation of surface meltwater from the ice sheet to the ocean. We examine this Inglefield Land coupled supraglacial-proglacial drainage system during the 2016–2019 melt seasons (July to August), using 137 Sentinel-2 and Landsat-8 visible/near-infrared satellite images. Two surface water metrics (supraglacial meltwater area fraction Am and proglacial river effective width We) are used to track spatio-temporal variations of surface meltwater moving through this drainage system. Satellite-derived Am and We are also compared with daily surface runoff simulations from the MAR v3.11 and MERRA-2 climate/SMB models, to estimate meltwater routing lag times and assess model performance. Satellite-derived Am and We are highly correlated (r2 = 0.85, p < 0.01), indicating that the coupled supraglacial-proglacial drainage system evacuates meltwater directly from the ice surface to the ocean with negligible subglacial storage or delays. Both remotely sensed metrics are positively correlated with modeled runoff, especially MAR (r2 = 0.81 and 0.77 for Am and We, vs. 0.66 and 0.64 for MERRA-2). Lagged MAR runoff (2 days, r2 = 0.87 and 0.82) match both metrics better than simultaneous MAR runoff and the optimal time lag for both metrics are 2 d. We conclude that 1) unlike the southwest GrIS, the coupled supraglacial-proglacial drainage system at Inglefield Land routes surface meltwater runoff directly off the ice surface to the proglacial zone, with virtually no subglacial capture of runoff by moulins; 2) most of the ∼2 d transit time occurs on the ice surface rather than in the proglacial zone; and 3) multi-temporal satellite imaging facilitates holistic, source-to-sink tracking of NW GrIS meltwater from the ice surface to the global ocean.