Document Type

Article

Publication Title

Journal of Geophysical Research: Earth Surfaces

Publisher

American Geophysical Union

Publication Date

3-28-2015

Abstract

The surface and basal boundary conditions exert an important control on the thermodynamic state of the Greenland Ice Sheet, but their representation in numerical ice sheet models is poorly constrained due to the lack of observations. Here we investigate a land-terminating sector of western Greenland and (1) quantify differences between new observations and commonly used boundary condition data sets and (2) demonstrate the impact of improved boundary conditions on simulated thermodynamics in a higher-order numerical flow model. We constrain near-surface temperature with measurements from two 20mboreholes in the ablation zone and 10m firn temperature from the percolation zone. We constrain basal heat flux using in situ measurement in a deep bedrock hole at the study area margin and other existing assessments. To assess boundary condition influences on simulated thermal-mechanical processes, we compare model output to multiple full-thickness temperature profiles collected in the ablation zone.Our observation-constrained basal heat flux is 30mW m2 less than commonly used representations. In contract, measured near-surface temperatures are warmed than common surface warmer than common surface temperature data sets by up to 15 degrees C. Application of lower basal heat flux increases a model cold bias compared to the measured temperature profiles and causes frozen basal conditions across the ablation zone. Temperate basal conditions are reestablished by our warmer surface boundary. Warmer surface ice and firn can introduce several times more energy to the modeled ice mass than what is lost at the bed from reduced basal heat flux, indicating that the thermomechanical state of the ice sheet is highly sensitive to near-surface effects.

DOI

10.1002/2014JF003375

Comments

An edited version of this paper was published by AGU. Copyright (2015) American Geophysical Union.

Rights

© 2015 American Geophysical Union

Recommended Citation

Meierbachtol, T. W., J. T. Harper, J. V. Johnson, N. F. Humphrey, and D. J. Brinkerhoff (2015), Thermal boundary conditions on western Greenland: Observational constraints and impacts on the modeled thermomechanical state, J. Geophys. Res. Earth Surf., 120, 623–636, doi:10.1002/2014JF003375.

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