Estimates of basal and englacial thermal conditions of the Antarctic ice sheet

Abstract We conduct an ensemble of simulations of the englacial temperature field of the Antarctic ice sheet to gauge the sensitivity to uncertainties in geothermal heat flow, surface climatic conditions, ice thermodynamics and dynamics. We compare the modeled temperature fields with observational constraints, including deep-borehole temperature measurements, englacial temperatures retrieved from the Soil Moisture and Ocean Salinity satellite observations, and the distribution of subglacial lakes to determine the most likely boundary conditions. Results show that temperate basal conditions prevail over 60% of the Antarctic ice sheet, with a mean basal melt rate of 6.9 mm a −1 . The ensemble mean subglacial meltwater production over the grounded ice sheet is 69 Gt a −1 , with a contribution of 51% from geothermal heat and 49% from frictional heat. While geothermal heat flow remains the largest source of uncertainty, heat flow datasets leading to colder conditions tend to fit englacial temperature measurements better. However, ice thermomechanical approximations influence the shape of temperature profiles and may, in some cases, be more important than the geothermal heat flow. Furthermore, since frictional heat contributes significantly to basal melt in regions hosting fast-flowing glaciers, uncertainties in basal slipperiness affect the basal melt estimates as much as the geothermal heat flow.