Calibration and validation of the CryoSat-2 radar altimeter: field studies on the Greenland Ice Sheet
Detailed time series of ice motion data were collected from a transect at a land-terminating margin of the Greenland Ice Sheet between May 2008 and May 2013. The transect consisted of 7 GPS units extending to ~120km inland. The ice-motion data, collected in conjunction with observations of ice-sheet melt and runoff, enabled the coupling between surface melt and ice dynamics to be investigated over a variety of temporal and spatial scales. We observed that the effect of surface meltwater penetration to the ice sheet bed is to perturb the subglacial hydrology at the ice-bed interface causing the ice sheet to flow faster in summer. However, we found that during summers of extreme melt, such as in 2012 (the most extreme melt-summer observed to date on Greenland), the ice sheet at our land-terminating margin flowed more slowly than in the average melt year of 2009, due principally to slower winter flow following faster summer flow. These findings suggest that the annual motion of land-terminating margins of the ice sheet, and thus the projected dynamic contribution of these margins to sea level rise, is insensitive to melt volumes commensurate with temperature projections for 2100. Our data also revealed short-term (<30 day) surface elevation change due to hydraulic jacking of up to 0.5m magnitude. As such, satellite missions should be cautioned against using differencing in ice-sheet elevation between summer melt-seasons in order to avoid erroneous estimates of dh/dt and thus errors in mass change.
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