Limits to future expansion of surface-melt-enhanced ice flow into the interior of western Greenland

Moulins are important conduits for surface meltwater to reach the bed of the Greenland Ice Sheet. It has been proposed that in a warming climate, newly formed moulins associated with the inland migration of supraglacial lakes could introduce surface melt to new regions of the bed, introducing or enhancing sliding there. By examining surface strain rates, we found that the upper limit to where crevasses, and therefore moulins, are likely to form is ∼1600m. This is also roughly the elevation above which lakes do not drain completely. Thus, meltwater above this elevation will largely flow tens of kilometers through surface streams into existing moulins downstream. Furthermore, results from a thermal ice sheet model indicate that the ∼1600m crevassing limit is well below the wet-frozen basal transition (∼2000m). Together, these data sets suggest that new supraglacial lakes will have a limited effect on the inland expansion of melt-induced seasonal acceleration. Key Points Greenland Ice Sheet meltwater volumes are increasing notably at high elevations Low strain rates limit the likelihood of moulin formation at high elevations High-elevation meltwater will reach an already wet bed at lower elevations