Community Heat Flow Recommendations: Suitable Basal Boundary Conditions for Greenland and Antarctica in ISMIP7

Mareen Lösing, William Colgan, Tobias Stål , Jörg Ebbing, Anne G. Busck, Tong Zhang, Hélène Seroussi, Felicity McCormack, Dominik Fahrner, Leigh Stearns, Synne H. Svendsen

Geothermal heat flow (GHF) influences ice-sheet thermal conditions, affecting
ice flow by sliding and deformation. However, GHF distribution under polar
ice-sheets remains poorly constrained, with few direct borehole-derived
estimates and large discrepancies between glaciological and geophysical
models caused by methodological differences and data limitations. As a result,
many ice-sheet models rely on uniform GHF estimates, ensemble averages, or
outdated fields that oversimplify reality. The choice of GHF product can lead to
significantly different thermal conditions simulated at the ice-bed interface, which
affects the projected evolution of ice-sheets under climate warming.
Therefore, we conduct an expert elicitation survey to identify the most suitable
GHF fields for use as basal boundary conditions in ice-sheet modelling,
particularly for the Ice-Sheet Modelling Intercomparison Project for CMIP7
(ISMIP7). GHF fields generally fall into three categories: (1) outdated due to
improved data availability, (2) overly simplified parameterizations, and (3)
current and preferred. For GHF fields that rank highly in the survey, we discuss
uncertainty, data dependency and guide their use in different applications.
Finally, we recommend two Antarctic and one Greenlandic GHF field(s) for
ISMIP7.