Observed runoff, jökulhlaups and suspended sediment load from the Greenland ice sheet at Kangerlussuaq, West Greenland, 2007 and 2008

Abstract

This study fills the gap in hydrologic measurements of runoff exiting a part of the Greenland ice sheet (GrIS), the Kangerlussuaq drainage area, West Greenland. The observations are of value for obtaining knowledge about the terrestrial freshwater and sediment output from part of the GrIS and the strip of land between the ice sheet and the ocean, in the context of varying ice-sheet surface melt and influx entering the ocean. High-resolution stage, discharge and suspended sediment load show a decrease in runoff of~25% and in sediment load of~40% from 2007 to 2008 in response to a decrease in the summer accumulated number of positive degree-days. During the 2007 and 2008 runoff seasons, jö kulhlaups were observed at Kangerlussuaq, drained from an ice-dammed lake at the margin of the GrIS.

Hydrologic controls on coastal suspended sediment plumes around the Greenland Ice Sheet

“…As a proxy for meltwater runoff from the ice sheet, PDD does not take into account meltwater routing or storage in the glacier and in proglacial systems, which will affect both timing and intensity of meltwater release. Future studies need to incorporate runoff models tuned by in situ discharge observations such as Mernild and Hasholt (2009) and Rennermalm et al (2011). As discussed above, using SSC to represent plume characteristics has its limitations due to the site-specific calibration of MODIS reflectances, the lack of validation for higher extrapolated SSC values from the empirical model, and the spatial aggregation used to overcome the poor temporal sampling.…”

“…Here, PDDs are used untransformed as a broad-scale, simple proxy for meltwater production. While not a true approximation for meltwater runoff, PDDs have been used in previous studies to represent melt intensity (Smith et al, 2003) and have been compared to ice sheet hydrologic processes such as supraglacial lake drainage and river discharge (Georgiou et al, 2009;Mernild and Hasholt, 2009) As a proxy for meltwater volume produced within each hydrologic drainage basin, the aforementioned PDD data were totaled over topographically determined basins and assumed to drain only to corresponding ice sheet outlet glaciers and rivers at the ice sheet edge.…”

“…However, its release from the ice sheet edge to the ocean remains largely unstudied. Existing research consists of a handful of modeling efforts (Bøggild et al, 1999;Lewis and Smith, 2009;Mernild et al, , 2011 and site-specific field studies (Rasch et al, 2000;Stott and Grove, 2001;Chu et al, 2009;Mernild and Hasholt, 2009;McGrath et al, 2010).…”

Evidence of meltwater retention within the Greenland ice sheet

“…Direct observations of ice sheet meltwater runoff extending over multiple years (Van den Broeke et al, 2011a) and ice sheet runoff losses through river discharge are scarce for Greenland (Ahlstrøm et al, 2002;Cowton et al, 2012;Mernild and Hasholt, 2009;Rennermalm et al, 2012). Instead, these losses are inferred from satellite gravity anomalies (Chen et al, 2011;Harig and Simons, 2012;Luthcke et al, 2006;Ramillien et al, 2006;Velicogna and Wahr, 2005), remotely-sensed elevation changes at the ice sheet surface (Krabill et al, 2004;Pritchard et al, 2009) or surface mass balance models (Box et al, 2006;Van den Broeke et al, 2009a;Ettema et al, 2009;Fettweis, 2007;Hanna et al, 2008;Mernild et al, , 2010bVernon et al, 2013).…”

“…In southwestern Greenland, an area with prominent surface meltwater lakes (Selmes et al, 2011), 40 % of lakes store water and freeze up in winter months with remaining lakes either draining slowly (37 %), quickly (14 %), or its state cannot be determined (8 %) (Selmes et al, 2013). Sudden drainage of ice sheet supra- (Bartholomew et al, 2011;Doyle et al, 2013), en-, sub- (Mathews, 1963), and proglacial meltwater lakes (Mernild and Hasholt, 2009;Russell, 2009;Russell et al, 2011) can result in pronounced river discharge anomalies.…”