Satellite radar interferometry data reveals that the grounding line of
Petermann Glacier, Greenland migrates by several kilometers during the
tidal cycle, bringing pressurized, subsurface, warm ocean waters in
regular contact with a large sector of grounded ice. We use the
Massachusetts Institute of Technology general circulation model in two
dimensions to calculate the ice melt rates as a function of grounding
zone width and ocean thermal forcing. Ice melt rates are found to be
higher in the grounding zone cavity than anywhere else in the ice shelf
cavity. The melt rates increase sub-linearly with the width of the
grounding zone and ocean thermal forcing. The model results agree well
with remote sensing estimates of ice melt. High basal ice melt rates in
tidally-flushed grounding zones imply that marine-terminating glaciers
are more sensitive to ocean thermal forcing than anticipated, which will
increase their projected contribution to sea level rise.