Seasonal evolution of basal conditions within Russell sector, West Greenland, inverted from satellite observations of surface flow

Abstract

Abstract. Increasing surface melting on the Greenland ice sheet requires better constraints on seasonally evolving basal water pressure and sliding speed. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of two weeks. We then apply the inverse control method using Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface-velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of a effective-pressure based hard-bed friction law. We find for valley bottoms or "troughs" in the bed topography, the changes in basal conditions directly respond to local water pressure variations, while the link is more complex for subglacial "ridges" which are often non-locally forced. At the catchment scale, in-phase variations of the water pressure, surface velocities, surface-runoff variations are found.Our results show that time-series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice-flow models.