Ice Surface Change Drives Subglacial Hydrologic Reorganization and Interior Speedup in Northwest Greenland

ABSTRACT. Changes in ice surface elevation and slope influence subglacial water pressure and sliding velocity. Leveraging decadal scale changes in ele- vation observed by the Ice, Cloud, and land-Elevation satellite (ICESat) and ICESat-2 missions, we use coupled subglacial hydrology–ice dynamics model- ing applied to a section of the northwest Greenland Ice Sheet to explore i) how decadal scale changes in ice surface elevation influence changes in win- ter background state subglacial hydrology and corresponding ice velocity, and ii) how much glacier seasonal response is attributable to geometry compared to environmental forcing. Our simulations suggest a complex reorganization of the subglacial hydrologic system between 2004 and 2020, as a result of changes in surface elevation, which drives the redistribution of freshwater flux between fjords, an overall acceleration trend in the interior, and an increase in background basal melt. We also find that the winter background state of the subglacial system modulates the seasonal response. This demonstrates a potential feedback that exacerbates mass loss from the Greenland Ice Sheet as surface elevation evolves, while also highlighting the subtleties involved in accounting for changes in effective pressure, ice velocity, and basal melt due to changes in subglacial hydrology.