Preprints
https://doi.org/10.5194/tc-2022-40
https://doi.org/10.5194/tc-2022-40
 
17 Feb 2022
17 Feb 2022
Status: this preprint is currently under review for the journal TC.

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

Joseph A. MacGregor1, Winnie Chu2, William T. Colgan3, Mark A. Fahnestock4, Denis Felikson1,5, Nanna B. Karlsson3, Sophie M. J. Nowicki6, and Michael Studinger1 Joseph A. MacGregor et al.
  • 1Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America
  • 2Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, United States of America
  • 3Geological Survey of Denmark and Greenland, Copenhagen, Denmark
  • 4Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America
  • 5Universities Space Research Association, Columbia, Maryland, United States of America
  • 6Department of Geology, University at Buffalo, Buffalo, New York, United States of America

Abstract. The basal thermal state (frozen or thawed) of the Greenland Ice Sheet is under-constrained due to few direct measurements, yet knowledge of this state is becoming increasingly important to interpret modern changes in ice flow. The first synthesis of this state relied on inferences from widespread airborne and satellite observations and numerical models, for which most of the underlying datasets have since been updated. Further, new and independent constraints on the basal thermal state have been developed from analysis of basal and englacial reflections observed by airborne radar sounding. Here we synthesize constraints on the Greenland Ice Sheet’s basal thermal state from boreholes, thermomechanical ice-flow models that participated in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), BedMachine v4 bed topography, Making Earth Science Data Records for Use in Research Environments (MEaSUREs) multi-year surface velocity mosaic v1, and multiple inferences of a thawed bed from airborne radar sounding. Most constraints can only identify where the bed is likely thawed rather than where it is frozen. This revised synthesis of the Greenland likely Basal Thermal State version 2 (GBaTSv2) indicates that 32 % of the ice sheet’s bed is likely thawed, 39 % is likely frozen, and the remainder (29 %) is too uncertain to specify. Although the spatial pattern of GBaTSv2 is broadly similar to the previous synthesis, including a scalloped frozen core and thawed outlet-glacier systems, the likely basal thermal state of nearly half (48 %) of the ice sheet has changed designation. This revised synthesis suggests that more of northern Greenland is likely thawed at its bed, and conversely that more of southern Greenland is likely frozen, both of which influence interpretation of the ice sheet’s present subglacial hydrology and models of its future evolution. The GBaTSv2 dataset, including both code that performed the analysis and the resulting raster products, is freely available at https://doi.org/10.5281/zenodo.5714527.

Joseph A. MacGregor et al.

Status: open (until 03 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of MacGregor et al “GBaTSv2: A revised synthesis of the likely basal thermal state of the Greenland Ice Sheet“', Andy Aschwanden, 29 Apr 2022 reply
  • RC2: 'Comment on tc-2022-40', Anonymous Referee #2, 29 Apr 2022 reply

Joseph A. MacGregor et al.

Data sets

GBaTSv2: Greenland Ice Sheet Likely Basal Thermal State version 2, draft dataset+code Joseph A. MacGregor https://doi.org/10.5281/zenodo.5714527

Joseph A. MacGregor et al.

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Short summary
Where the bottom of the Greenland Ice Sheet is frozen and where it is thawed is not well known, yet knowing this state is increasingly important to interpret modern changes in ice flow there. We produced a second synthesis of knowledge of the basal thermal state of the ice sheet using airborne and satellite observations and numerical models. About one third of the ice sheet’s bed is likely thawed, slightly more than one third is likely frozen, and the remainder is too uncertain to specify.