Abstract
Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.
Highlights
Acceleration of marine-terminating glaciers in Greenland in recent decades has significantly increased the contribution of the ice sheet to sea level (Enderlin et al, 2014)
Due to thickening of the ice via advection, estimated SMRNSS for each set of flowlines are less than those estimated for the steady state scenario, with mean decreases in melt rate of 15 and 28% for the eastern and western flowlines, respectively
Melt rates broadly decrease with distance from the Kangiata Nunaata Sermia (KNS) grounding line and moving from east to west across the ice tongue
Summary
Acceleration of marine-terminating glaciers in Greenland in recent decades has significantly increased the contribution of the ice sheet to sea level (Enderlin et al, 2014). Fitting the TanDEM-X elevations to the OIB ATM elevations results in a root mean square error of FIGURE 5 | (A) Ice freeboard and thickness (m) on 17 March and 27 May 2013 with distance from KNS terminus for the eastern flowlines, where solid lines are means from 10 flowlines (Figure 4) and dashed lines are moving averages (MAVs) of the mean; (B) Steady state estimated submarine melt rate (SMRSS) for eastern flowlines, with dashed trendlines and shaded error ranges. If the tongue was thickest in April, our May melt rate estimates would be an underestimate; without additional DEMs we cannot address this possibility Another potential source of error derives from smoothing the ice freeboard near the glacier grounding line, where presmoothed freeboard values decrease sharply, as compared with smoothed values (see Figures 5A, 6A). While smoothing out fracturing associated with large crevasses on the ice tongue helps to reduce noise in the SMR estimates, the resultant reduction in freeboard gradient significantly lowers our SMRs near the grounding line, which should be considered minimum estimates of melt rate in this location
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