Abstract
Land-terminating sectors of the Greenland ice sheet flow faster in summer after surface meltwater reaches the subglacial drainage system. Speedup occurs when the subglacial drainage system becomes saturated, leading to a reduction in the effective pressure which promotes sliding of the overlying ice. Here, we use observations acquired by the Sentinel-1a and b synthetic aperture radar to track changes in the speed of land-terminating glaciers across a 14,000 km2 sector of west-central Greenland on a weekly basis in 2016 and 2017. The fine spatial and temporal sampling of the satellite data allows us to map the speed of summer and winter across the entire sector and to resolve the weekly evolution of ice flow across the downstream portions of five glaciers. Near to the ice sheet margin (at 650 m.a.s.l.), glacier speedup begins around day 130, persisting for around 90 days, and then peaks around day 150. At four of the five glaciers included in our survey the peak speedup is similar in both years, in Russell Glacier there is marked interannual variability of 32% between 2016 and 2017. We present, for the first time, seasonal and altitudinal variation in speedup persistence. Our study demonstrates the value of Sentinel-1’s systematic and frequent acquisition plan for studying seasonal changes in ice sheet flow.
Highlights
In recent decades the Greenland Ice Sheet has lost ice at an increasing rate, rising by 89% between 2011–2014 relative to 1992–2011 [1,2]
Rising air temperatures lead to increased surface melting, which can in turn lead to an increase in the amount of water feeding into the subglacial drainage system [10] after supraglacial lakes drain or moulins open [9,10]
The retrieval of summer velocities is limited to within ~30 km of the ice sheet margin where there is a sufficient amount of persistent physical features to be able to track motion
Summary
In recent decades the Greenland Ice Sheet has lost ice at an increasing rate, rising by 89% between 2011–2014 relative to 1992–2011 [1,2]. At low elevations (under 1000 m), seasonal changes in the movement of Greenland’s glaciers are thought to be dominated by short-term events, typically lasting between 1 day to 1 week during the summer [25,26], with ice speeds increasing by 100% to 150% relative to winter [20,27] Resolving such changes has been a challenge, because observations of ice sheet flow have historically been made using episodically acquired satellite imagery [7,11,12] and GPS sensors installed at point locations on the ice sheet [14,19,25]. We use a sequence of Sentinel-1a and 1b SAR images to track seasonal changes in ice sheet flow across a land-terminating sector of the Greenland Ice Sheet between 2014 and 2017
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