Greenland Ice Sheet hydrology and dynamics: the role of surface and basal topography

The Greenland Ice Sheet (GrIS) is an important and growing contributor to global sea level rise. However, the long-term influence of meltwater hydrology on GrIS dynamics (i.e. hydro-dynamics) and mass balance in a warming climate remains uncertain, partly due to our limited understanding of controls governing the large-scale spatial structure of surface drainage. Although the bed-to-surface transfer of basal topographical variations is thought to exert a key influence on surface hydrology, this is yet to be tested at the ice sheet-scale. Focussing on the contemporary GrIS, I use recent developments in the theory of bed-to-surface transfer to demonstrate that bed properties can be used to predict the surface relief of the ice sheet. Although the approach is approximate, the magnitude and spatial pattern of discrepancies with real topography are consistent with the limitations of the theory and known uncertainties of the input datasets. Additional analyses show that surface relief, which is predominantly controlled by the bed-to-surface transfer of basal topography, preconditions the large scale spatial structure of surface drainage. It follows that the spatial structure of surface drainage depends strongly on the transfer of basal topography to the ice surface. Based on these findings, I estimate the changing future distribution of surface lakes on the GrIS, which is crucial for hydro-dynamics as lakes can initiate surface-to-bed hydraulic connections through thick ice. The total volume of surface lakes is projected to increase sharply – by 172-270% – during the 21st century though the rate of increase slows between 2100 and 2300. The regional distribution of surface lakes is also projected to shift on the GrIS, from the SW to the W, NW and NE. Effects of the changing surface relief on surface lake distribution can be neglected during the 21st century, but projections beyond 2100 should incorporate them.