Constraining the geothermal heat flux in Greenland at regions of radar-detected basal water

Soroush Rezvanbehbahani,Gordon K A Oswald,Ralf Greve,Leigh A Stearns,C J Van Der Veen

doi:10.1017/jog.2019.79

Abstract

AbstractThe spatial distribution of basal water critically impacts the evolution of ice sheets. Current estimates of basal water distribution beneath the Greenland Ice Sheet (GrIS) contain large uncertainties due to poorly constrained boundary conditions, primarily from geothermal heat flux (GHF). The existing GHF models often contradict each other and implementing them in numerical ice-sheet models cannot reproduce the measured temperatures at ice core locations. Here we utilize two datasets of radar-detected basal water in Greenland to constrain the GHF at regions with a thawed bed. Using the three-dimensional ice-sheet model SICOPOLIS, we iteratively adjust the GHF to find the minimum GHF required to reach the bed to the pressure melting point, GHFpmp, at locations of radar-detected basal water. We identify parts of the central-east, south and northwest Greenland with significantly high GHFpmp. Conversely, we find that the majority of low-elevation regions of west Greenland and parts of northeast have very low GHFpmp. We compare the estimated constraints with the available GHF models for Greenland and show that GHF models often do not honor the estimated constraints. Our results highlight the need for community effort to reconcile the discrepancies between radar data, GHF models, and ice core information.

Highlights

Basal ice temperature plays an important role in controlling ice velocity and ice-sheet geometry and discharge
For each of these datasets, we perform five different simulations with all the geothermal heat flux (GHF) models considered in this study: at the locations where GHF is not being adjusted, the GHF values remain fixed as prescribed by each GHF model
We use the locations of basal water in Greenland, detected by two radar datasets to constrain the GHF in Greenland using SICOPOLIS numerical model

Summary

Introduction

Basal ice temperature plays an important role in controlling ice velocity and ice-sheet geometry and discharge. The effect of each of these components on basal conditions varies spatially, primarily based on ice thickness, velocity and tectonic setting. Among these sources, GHF has the largest uncertainty range in the interior regions; apart from a handful of deep ice cores, direct measurements of GHF are not available under the ice sheet. Seismic tomography models, based on structural similarity functionals, are used to estimate the global GHF (Shapiro and Ritzwoller, 2004) (Fig. 1d), and Greve (2005) and Greve (2019) modify the empirical GHF estimates of Pollack and others (1993) to match the modeled and measured basal temperatures in Greenland ice cores

Results

Discussion

Conclusion