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

Aleah Nicholson Sommers , Aaron Stubblefield, Lauren Andrews, Colin R. Meyer, Benjamin Smith

 Changes in ice surface elevation and slope influence subglacial water pressure and sliding velocity. Leveraging changes in elevation observed by the Ice, Cloud, and land-Elevation satellite (ICESat) and ICESat-2 missions, we use coupled subglacial hydrology--ice dynamics modeling applied to a section of the northwest Greenland Ice Sheet to explore i) how decadal scale changes in ice surface elevation influence changes in winter background subglacial hydrology and corresponding ice velocity, and ii) how much seasonal response is attributable to geometry versus environmental forcing. Our simulations suggest complex reorganization of the subglacial hydrologic system between 2004 and 2020, resulting from changes in surface elevation, driving redistribution of freshwater flux, an overall acceleration trend in the interior, and an increase in background basal melt. Without changing hydrological conditions, geometry changes alone lead to greater interior acceleration, suggesting that changes in the subglacial system help to mitigate this speedup. We also find that the winter background state of the subglacial system modulates the seasonal response. This work demonstrates feedbacks that influence mass loss from the Greenland Ice Sheet as surface elevation evolves, highlighting the subtleties involved in accounting for changes in effective pressure, ice velocity, and basal melt due to changes in subglacial hydrology.