Modelling of the dynamics of Fimbulisen, Antarctica
Final Report Abstract
This project modelled the temperature field and the flow velocities of Fimbulisen, Antarctica, an ice shelf that drains Jutulstraumen, East Antarctica. The numerical model uses a continuum mechanical approach and solves the momentum balance in shallow shelf approximation and the 3D heat transport equation. The ice is treated as a non-Newtonian fluid in which the viscosity depends via Hookes rate factor on temperature and an enhancement factor is taken into account. The equations for the 3D temperature model and the 2D flow model are solved using COMSOL. The modelled temperature field is based on remote sensing basal melt rates and observed flow velocities. It shows the cold core of ice that is transported by Jutulstraumen into the ice shelf and warmer areas in the slower moving parts. Future warming will effectively increase the temperatures throughout the ice column in the slower-moving parts. In areas where advection dominates the ice temperature, however, only the upper part of the ice shelf will be affected. A surface temperature increase will therefore affect the shear between the fast- and slow-moving areas. In a second part of the project the flow field of Fimbulisen was modelled, using the temperature field for the viscosity of the ice. It turned out that the velocity field does not match the observed field in magnitude and direction in the fast moving part where Jutulstraumen turns into Trolltunga. Therefore, efforts have been made to incorporate the softening effect of cracks and damage into the model. For that purpose radar imagery and radio echo sounding data has been used to identify areas of similar damage characteristics. In each of these areas an individual enhancement factor has been used for accounting for softening due to damage. Some ten thousand simulations have been run and analysed using a misfit parameter. None of the parameter combinations lead to a realistic flow field in the central part, neither very soft shear margins, nor soft main part, nor any other combination. It remains unclear why the modelled flow becomes decelerated before it starts to accelerate towards the calving front. However, analysing radar imagery and radio echo sounding data for the purpose of identifying different domains has turned out to be quite useful for understanding the cause for internal structure and the stress states.
Publications
- Glaciological investigations of the dynamics of the Fimbulisen ice shelf, EGU 2010
Sinisalo, Langley, Anschütz, Isaksson, Hamran, Øyan, Hagen, Kohler, Nøst, A. Humbert, Goodwin
- Investigation of a rift zone in the western Fimbulisen by means of airborne radio echo sounding, satellite imagery, and ice flow modelling, EGU 2010
Humbert & Steinhage
- The thermal regime of Fimbulisen. Annals of Glaciology 51(55), 56-64, 2010
A. Humbert
- The evolution of the western rift area of the Fimbul Ice Shelf, Antarctica, The Cryosphere, 5, 931-944, 2011
Humbert, A. and Steinhage, D.
- (2014), Complex network of channels beneath an Antarctic ice shelf, Geophys.Res. Lett.,41, 1209–1215
Langley, K., A. vonDeschwanden, J. Kohler, A. Sinisalo, K. Matsuoka, T. Hattermann, A. Humbert, O. A. Nøst, and E. Isaksson
(See online at https://doi.org/10.1002/2013GL058947)
