Sensitivity of the Northeast Greenland Ice Stream to uncertainties in geothermal heat flux

The Northeast Greenland Ice Stream (NEGIS) drains 12 % of the Greenland Ice Sheet and is largely driven by basal sliding. The onset of NEGIS is further inland than commonly observed in Greenland, and suggested to be initiated by an area of elevated geothermal heat flux. Geothermal heat flux impacts the basal thermal regime and the distribution of basal meltwater, both crucial for ice stream dynamics. However, spatial distribution and magnitude of geothermal heat flux is largely unknown. Previous sensitivity studies inverted for basal conditions using observed surface velocities, masking errors in the geothermal heat flux. We aim to quantify the impact of uncertainties in the geothermal heat flux on ice dynamics of NEGIS, and disentangle errors originating from ice rheology (internal ice flow) and basal water production (sliding). We use the Ice Sheet System Model (ISSM), where thermomechanical ice flow is fully coupled to subglacial hydrology. Our results, which explicitly simulate the impact of water pressure at the base of the ice, indicate that ice streams may be more sensitive to geothermal heat uncertainties than previously found. Including a better representation of the geothermal heat and effective pressure is crucial for estimating the potential contribution from fast flowing ice streams such as NEGIS to sea level rise in the coming centuries.