There is currently poor scientific agreement whether the ice-bed interface is frozen or thawed beneath approximately one-third of the Greenland ice sheet. This disagreement in basal thermal state results, at least partly, from a diversity of opinion in the subglacial geothermal heat flow basal boundary condition used in different ice flow models. Here, we apply the seven Greenland geothermal heat flow maps in widespread use to a 10,000-year spin-up of the Community Ice Sheet Model (CISM) that conforms to Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) protocol. This seven-simulation ensemble produces a wide spread in basal ice temperatures that exceed 10°C over large areas of the ice-bed interface. As the CISM spin-up nudges the simulated ice sheet by adjusting basal friction coefficients, differences in basal thermal state associated with choice of heat flow map result in differences in surface ice velocity at transient equilibrium. This highlights the direct, and non-trivial, influence of choice of geothermal boundary condition on the simulated equilibrium thermal state of the ice sheet. We suggest that future ice-flow model intercomparisons should employ a range of geothermal basal boundary conditions, and limit direct intercomparisons to simulating employing a common geothermal heat flow map.

Greenland Ice Sheet,model,geothermal heat flux,ice dynamics