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Quantifying Greenland Iceberg Melt Rates using Remotely-sensed Data


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The investigators propose to implement a new remote sensing technique for deriving iceberg volume changes
in order to estimate submarine melt rates in key fjords around the Greenland Ice Sheet periphery. The fluxes of solid ice and liquid freshwater from the Greenland Ice Sheet are important contributors to sea level rise and ocean freshening. Solid fluxes come in the form of icebergs calved from marine-terminating glacier margins. Freshwater fluxes are comprised of surface meltwater runoff and submarine melting at calving margins. As icebergs drift away from the margin, however, they are subject to submarine melting and thus constitute an additional source of freshwater release to the ocean. Variations in the magnitude and spatial distribution
of freshwater fluxes in glacial fjords and adjacent ocean basins can impact the ocean?s stratification, circulation, and ecological structure as well as ice-ocean interactions that influence ice flow, so it is important that spatial and temporal variations in melting are quantified. Melt rates will be obtained near the margins of about 20 large outlet glaciers using an extensive collection of ~0.5 m-resolution WorldView stereo satellite images compiled by the Polar Geospatial Center. Digital elevation models (DEMs) will be constructed from available stereo pairs using
the NASA Ames Stereo Pipeline software implemented on the University of Maine supercomputing cluster. Differencing the co-registered sequential DEMs acquired ~5-30 days apart yields an estimate of the change in iceberg freeboard (i.e., surface elevation above sea level) which
can be converted to an iceberg draft assuming hydrostatic equilibrium. The PIs contend that after accounting for elevation change due to surface melting and tides, the residual difference in iceberg freeboard between the DEMs must be due to submarine melting. This work will provide new insights for studies focused on ice-ocean interactions and freshwater input to high latitude oceans. The project provides support for an early-career scientist and for an undergraduate student. Mentoring the undergraduate research assistant will give the early-career scientist valuable advising experience, and the student will develop data-analysis and problem solving skills that are not readily obtained by in-class instruction.