GBaTSv2: a revised synthesis of the likely basal thermal state of the Greenland Ice Sheet

Abstract. The basal thermal state (frozen or thawed) of the Greenland Ice Sheet is under-constrained due to few direct measurements, yet knowledge this becoming increasingly important interpret modern changes in ice flow. first synthesis relied on inferences from widespread airborne and satellite observations numerical models, for which most underlying datasets have since been updated. Further, new independent constraints developed analysis englacial reflections observed by radar sounding. Here we synthesize Sheet's boreholes, thermomechanical ice-flow models that participated Model Intercomparison Project CMIP6 (ISMIP6; Coupled Phase 6), IceBridge BedMachine v4 bed topography, Making Earth Science Data Records Use Research Environments (MEaSUREs) Multi-Year Velocity Mosaic v1 multiple a thawed Most can only identify where likely rather than it frozen. This revised Basal Thermal State version 2 (GBaTSv2) indicates 33 % sheet's thawed, 40 frozen remainder (28 %) too uncertain specify. spatial pattern GBaTSv2 broadly similar previous synthesis, including scalloped core outlet-glacier systems. Although nearly half (46 sheet changed designation, assigned (or vice versa) less 6 sheet. suggests more northern at its conversely southern frozen, both influence interpretation present subglacial hydrology future evolution. dataset, code performed resulting datasets, freely available https://doi.org/10.5281/zenodo.6759384 (MacGregor, 2022).