Sediment plumes in Sondre Stromfjord, Greenland as a proxy for runoff from the Greenland ice sheet.

摘要

Recent warming has been particularly acute in the Arctic, leading to a strongly negative mass balance of the Greenland Ice Sheet (GrIS). Meltwater runoff is an important component of an ice sheet's surface mass balance, although in situ measurements to quantify run-off are hindered by logistical difficulties associated with the large, remote and spatially diverse nature of the ice sheet. Modeling studies suggest that run-off accounts for approximately 30-50% of the annual mass loss from the ice sheet, however, there is a need to more accurately quantify run-off with empirical measurements. The purpose of this research is to determine if remote sensing can be used to characterize the onset, duration and intensity of meltwater runoff. The primary field site includes a 6,280 km2 basin of the ice sheet, which runs off into the Watson River before flowing into Sondre Stromfjord, the longest fjord in west Greenland. The onset and duration of runoff into Sondre Stromfjord was compiled using the MODerate-resolution Imaging Spectroradiometer (MODIS) Band 1 (620-670 nm, 250 m resolution) from 2001-2008. Over the 8 yr study period, plume formation occurred 10 days earlier. The onset of ablation at the S5 (490 m asl, 6 km from ice margin) Kangerlussuaq Transect automatic weather station and plume formation are positively correlated (r2=0.88, 2003-2008). Likewise, there is a positive correlation (r2=0.93) between the cessation of ablation and the waning of the plume. Sediment plume length variability throughout the 2007 and 2008 melt seasons is strongly correlated (r2=0.83) with a 4-day average Watson River discharge. This relationship is applied to plume length variability derived from MODIS imagery to reconstruct cumulative Watson River discharge. Reconstructed values using plume length overestimate measured discharge values by ∼10%.