Greenland ice sheet annual motion insensitive to spatial variations in subglacial hydraulic structure

We present ice velocities observed with global positioning systems and TerraSAR-X/TanDEM-X in a land-terminating region of the southwest Greenland ice sheet (GrIS) during the melt year 2012–2013, to examine the spatial pattern of seasonal and annual ice motion. We find that while 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. While absolute annual velocities vary substantially, the proportional contribution of summer motion to annual motion does not. These observations suggest that in land-terminating margins of the GrIS, subglacial hydrology does not significantly influence spatial variations in net summer speedup. Furthermore, our findings imply that not every feature of the subglacial drainage system needs to be resolved in ice sheet models.