Assessing uncertainties in modelling the thermal state of the Antarctic Ice Sheet

Many processes that influence the dynamic behaviour of the Antarctic ice sheet, such as basal sliding, ice rheology, and subglacial meltwater production, largely depend on the thermal state and how it evolves. However, significant uncertainties remain regarding the factors influencing basal and englacial temperatures, hindering the predictions of ice sheet models. These uncertainties pertain to geothermal heat flow, past and present surface climatic conditions, and the inherent complexity of ice flow models. In this study, we provide new estimates of englacial and basal thermal conditions and conduct an ensemble of simulations to quantify the impact of these factors on the basal thermal regime and assess their contributions to model uncertainty. We use observational constraints, including deep borehole measurements, englacial temperatures derived from SMOS satellite observations, and the presence of subglacial lakes, to evaluate the ensemble results and determine the most likely simulations. Although we find that geothermal heat flow remains the largest source of uncertainty, recently published heat flow data seem to better fit the observational constraints. Nevertheless, since the englacial temperature field is sensitive to the past climate history, accounting for variations in surface temperatures and accumulation rates over the last glacial-interglacial cycle results in colder temperature profiles and basal thermal conditions, which points to possible overestimation of thermal conditions based on present-day boundary conditions.