Articles | Volume 11, issue 1
The Cryosphere, 11, 319–329, 2017
The Cryosphere, 11, 319–329, 2017

Research article 31 Jan 2017

Research article | 31 Jan 2017

Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

Rupert Michael Gladstone1,2,3, Roland Charles Warner2, Benjamin Keith Galton-Fenzi2,4, Olivier Gagliardini5, Thomas Zwinger6, and Ralf Greve7 Rupert Michael Gladstone et al.
  • 1VAW, Eidgenössische Technische Hochschule Zürich, ETHZ, Zürich, Switzerland
  • 2Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Australia
  • 3Arctic Centre, University of Lapland, Rovaniemi, Finland
  • 4Australian Antarctic Division, Kingston, Tasmania, Australia
  • 5Univ. Grenoble Alpes, CNRS, IRD, IGE, 38000 Grenoble, France
  • 6CSC – IT Center for Science Ltd., Espoo, Finland
  • 7Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan

Abstract. Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.

Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.

A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.

Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary.

Short summary
Computer models are used to simulate the behaviour of glaciers and ice sheets. It has been found that such models are required to be run at very high resolution (which means high computational expense) in order to accurately represent the evolution of marine ice sheets (ice sheets resting on bedrock below sea level), in certain situations which depend on sub-glacial physical processes.