C14B-08:
Greenland Ice Sheet sediment dynamics with Landsat: Island-wide mapping shows sediment export controlled by ice discharge

Monday, 15 December 2014: 5:45 PM
Benjamin D Hudson1, Irina Overeem2, James P Syvitski3, Andreas Bech Mikkelsen4, Bent Hasholt4 and Mathieu Morlighem5, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Univ Colorado, Boulder, CO, United States, (3)University of Colorado at Boulder, CSDMS/INSTAAR, Boulder, CO, United States, (4)University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark, (5)University of California Irvine, Irvine, CA, United States
Abstract:
We conducted a satellite-based survey of Greenland Ice Sheet (GrIS) sediment processes using all images of Greenland in the Landsat7 archive (1999 – 2013). Imaging over 150 proglacial rivers near their ice sheet source to calculate median suspended sediment concentration (SSC) for the Landsat7 era, we find ice sheet evacuation of suspended sediment via rivers is highly spatially variable, with a small percentage of ice sheet termini evacuating sediment at elevated SSCs. Most (67 %) of termini had a median SSC value less than 1000 mg/l, while only 8% had values greater than 2000 mg/l, yet these termini with SSC in excess of 2000 mg/l export ~90 % of suspended sediment from the ice sheet. Combining surface ice velocity data and ice thickness data we find that ice discharge at ice sheet termini largely drives this spatial variability in SSC.

Though 1% of the Earth’s land surface area, using modeled ice sheet runoff we estimate that the GrIS exports 6 to 11 % of the total sediment export to the global ocean if all sediment is assumed to reach the ocean. Finally, we find river mouth SSC high enough to cause hyperpycnal flow to occur. Hence, sediment can at times be efficiently mobilized from ice sheet directly to fjord bottom/continental shelf.

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