Assessing the basal thermal state of the Greenland Ice Sheet from geothermal heat flux constraints

S. REZVANBEHBAHANI, L. A. STEARNS, C. J. VAN DER VEEN, G. K. A. OSWALD AND R. GREVE


Abstract

The spatial distribution of basal melt is a critical parameter for numerical ice sheet models. Current basal melt estimates of the Greenland Ice Sheet (GrIS) contain large uncertainties due to unknown boundary conditions, primarily from geothermal heat flux (GHF). In this study we constrain the GHF by incorporating information about the location of thawed and frozen bed conditions from two datasets; the first dataset is based on the intensity of reflected radar signals, and the second dataset is a synthesized compilation of ice sheet models, surface roughness, and radiostratigraphy. Using the three-dimensional ice sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum and maximum heat flux required at regions with thawed and frozen beds, respectively. By defining thresholds for 'too-high' and 'too-low' GHF values, we present an alternative approach for identifying thawed and frozen regions. We show that the basal ice in south Greenland requires unexpectedly high GHF values to reach the melting point, and is therefore likely frozen, unless geologic features such as mafic dyke intrusions locally affect the basal thermal condition. We also identify regions with likely thawed basal conditions to the west and south of the NGRIP site and upstream of Petermann Glacier. Other regions of thaw include the upstream regions of Jakobshavn Isbrae and Helheim Glacier. The majority of our GHF constraints are close to the mean GHF value of the North American plate (~ 56 mW/m2) and thus cannot by themselves predict the basal thermal state.


Journal of Glaciology (submitted).

 
Last modified: 2017-06-20