Fig. 1 : Champs de vitesse de surface modélisé. La ligne blanche représente la ligne d’échouage, la transition entre les zones de glace posées sur le socle et flottantes sur l’océan.
Ice, which forms from the accumulation of snowfall, behaves like a viscous fluid that flows under its own weight. The Antarctic ice cap is unique in that it rests on a bedrock with large areas below sea level, and is surrounded by large ice shelves which, due to water pressure, float on the oceans.
This particular configuration is subject to instability where a small disturbance, such as increased melting beneath the floating platforms, and could lead to a significant and irreversible retreat of the cap. Recent observations have shown a significant acceleration of some glaciers draining the cap, notably in the Amundsen Sea sector, suggesting that this mechanism may have been initiated.
For several years the IGE has been co-developing the Elmer/Ice polar cap model. It's mainly at the level of initial and boundary conditions that difficulties arise. For example, the conditions at the base are inaccessible to measurement, yet the resistance of the base to ice sliding can
vary over several orders of magnitude depending on the type of base and the presence of liquid water. The result is an extremely heterogeneous flow, with most of the ice drained by outlet glaciers, veritable rivers of ice within the cap, which can flow at a rate of a few kilometers per year, as illustrated in Figure. An adaptive mesh and data assimilation methods enable us to capture the flow velocities observed by satellites. Thanks to GENCI's resources, we and our partners in the European TiPACCS project have shown that the cap is currently in a stable configuration in the face of small disturbances.
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