Investigating Greenland Outlet Glacier Annual Motion in Response to Varying Subglacial Hydraulic Structure

Abstract:

The relationship between surface melting and ice motion will affect how the Greenland Ice Sheet responds to climate and the structure of the subglacial drainage system may be crucial in controlling how changing melt-rates impact ice motion. Several lines of evidence indicate that hydraulically efficient subglacial channels extend tens of km inland from land-terminating margins of the Greenland Ice Sheet during the melt-season. However, it remains unclear the extent to which water pressure variations in these drainage axes perturb ice-motion in areas both proximal and distal to the channels where the drainage system is likely hydraulically inefficient. Here, we present ice velocities observed with field based GPS and remotely sensed TerraSAR-X data across a land-terminating region of the south-west Greenland ice sheet during the melt-year 2012–2013, to examine the impact of varying drainage system structure on the spatial pattern of seasonal and annual ice motion. We find that whilst spatial variability in the configuration of the subglacial drainage system controls ice motion at short timescales, this configuration has negligible impact on the spatial pattern of the proportion of annual motion which occurs during summer. Whilst absolute annual velocities vary substantially, the proportional contribution of summer motion to annual motion does not. Subglacial hydrology does not therefore have a significant impact on the overall extent to which summer motion contributes to annual motion. These findings imply that the representation of hydrology in ice sheet models may be simplified.