Data analysis and numerical simulations for investigating Antarctic ice-shelf/ice-stream systems

The Antarctic ice shelves together with their inflowing ice streams and glaciers are important elements of the dynamics of the entire Antarctic ice because they drain approximately 90% of the coastward mass flux of the inland ice. We proposed to construct detailed numerical simulations of velocity fields with the software FESSACODE and COMSOL for the following shelves:

*	Brunt Ice Shelf,
*	Fimbulisen Ice Shelf,
*	George VI Ice Shelf,
*	Ross Ice Shelf

(see map), and to compare the results with remote sensing field data available in the literature and on the web. Originally, studies on the Amery and Hells Gate Ice Shelves were also envisaged; however, these studies were dropped due to limited data resources and available time.

For the simulations, it was required to put together accurate data-sets for their thickness, ice velocity, grounding line and surface temperature as input quantities. With their knowledge, ice-flow fields could be calculated, and the results be compared with measured velocities at selected surface points. The sensitivity of the ice flow was investigated with respect to the ice thickness, the inflow velocity, the position and extent of ice rises and rumples, the surface temperature, the enhancement factor in Glen's flow law and the density and distribution of crevasses. All these quantities affect the magnitude, orientation and distribution of the ice velocity.

The diagnostic computations demonstrated that the velocity distributions in any of the four ice shelves (Brunt, Fimbulisen, George VI, Ross) are strongly influenced by the distributions of the thickness, temperature and rate factor, and to a lesser extent (but still non-negligibly) by the flux boundary conditions along the grounding lines. Such diagnostic computations, in which for lack of detailed measurements the distributions of the temperature and rate factor of Glen's power law are to a large extent determined by educated guesses, do not provide sufficient information to constrain the velocity fields uniquely. Far more detailed data on temperature and rate factor distributions would be needed to that effect. A possible way out is to perform prognostic computations, in which the distributions of the temperature and enhancement factors follow from corresponding evolution equations. For temperature the procedure appears to be obvious as only the heat equation must be solved along with the equations for the motion. As for the stress law, the situation is more difficult: Here models for induced anisotropies must be incorporated, and these are presently not known for ice-shelf ice. So it turns out that full scale ice shelf analyses are required even to merely obtain a reliable information for the simplest diagnostic case.

Scientists

Prof. Kolumban Hutter, Ph.D.
Department of Mechanics
Darmstadt University of Technology

Prof. Dr. Ralf Greve
Institute of Low Temperature Science
Hokkaido University, Sapporo, Japan

Dr. Angelika Humbert
Institute of Geophysics
University of Münster

Research areas

	°South	°East
Brunt Ice Shelf	~ 75	335
Fimbulisen	~ 70	0
George VI Ice Shelf	~ 73	290
Ross Ice Shelf	~ 80	180

Publications

Humbert, A., T. Kleiner, C.-O. Mohrholz, C. Oelke, R. Greve and M. A. Lange. 2008. A comparative modeling study of the Brunt Ice Shelf - Stancomb-Wills Ice Tongue System. J. Glaciol. (in press).

Humbert, A. 2007. Numerical simulations of the ice flow dynamics of George VI Ice Shelf, Antarctica. J. Glaciol. 53 (183), 659-664.

Humbert, A. 2006. Numerical simulations of the ice flow dynamics of Fimbulisen. In: L. H. Smedsrud (ed.), Forum for Research into Ice Shelf Processes (FRISP) Report No. 17, pp. 67-78. Bjerknes Centre for Climate Research, Bergen, Norway. URL: http://www.uib.no/people/ngfls/frisp/FRISPRep17.html.

Humbert, A. and H. D. Pritchard. 2006. Numerical simulations of the ice flow dynamics of the Brunt Ice Shelf - Stancomb Wills Ice Tongue System. In: L. H. Smedsrud (ed.), Forum for Research into Ice Shelf Processes (FRISP) Report No. 17, pp. 85-97. Bjerknes Centre for Climate Research, Bergen, Norway. URL: http://www.uib.no/people/ngfls/frisp/FRISPRep17.html.

Humbert, A. 2005. Simulations of the flow of the Ross Ice Shelf, Antarctica: Parameter sensitivity tests and temperature-dependent rate factor. Doctoral thesis, Department of Mechanics, Darmstadt University of Technology, Germany. ISBN: 3-935868-10-3.

Humbert, A., R. Greve and K. Hutter. 2005. Parameter sensitivity studies for the ice flow of the Ross Ice Shelf, Antarctica. J. Geophys. Res. 110  (F4), F04022. doi: 10.1029/2004JF000170.

Homepage

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Research funding organisation

German Research Foundation

Project numbers: GR 1557/5, HU 412/39.
Funding period: October 2003 - September 2006