Historical understanding of ice sheet dynamics versus evolution of topography
Frédérique Rémy(1) , Benoît Legrésy(1) , and Laurent Testut(1)
18 av E. Belin,
31041 Toulouse CEDEX 9,
The ice sheet topography is one of the pertinent parameters related to the processes acting on ice sheet. Because it is a free surface, it description strongly helps in ice modelling. From the global scale to the km-scale, the topography hides the signature of the physical processes as well as the one of external forcing. The aim of this paper is to review the historical evolution of our ice modelling understanding with respect to the evolution in the altimetric sensors, in the mission orbits, in our comprehension of bias and in the data processing.
At the large scale, the first well described by the altimetric observations, it is mostly the validity and the parameter values of the Glen law that were looking for. As the topography evolves, the so called Glen exponent were found to be 1, then 3, then varying from 1 to 3 depending on the temperature. The first unexpected surprise offered by the altimetric observations was the discovery of large subglacial lakes, the first one the Astrolabe with the Seasat altimeter, then the Vostok one very soon after the ERS launch, before the discovery of numerous lakes around dome C and Vostok areas.
At the 100-km scale, two different undulations networks were pointing out. The first one, in the flow direction, is related to the propagation of anomaly from the outlet glacier up to the dome and exhibits that the flow direction does not always follow the surface slope direction. The second one, parallel to the flow with a wavelength of 250 km is still to be understanded, as the regular pattern of the outlet anomaly mapped with the help of the first network.
Even if the 10-km scale undulation were quickly well described, the evolution of the sensors, of the mission orbit, of our understanding of the altimetric bias and of the data processing yields to a better small-scale features description with the help of waveform shape. Thus, we are now able to characterize and describe km-scale. At this scale we observe the anisotropy of surface undulations related to the ice properties, we describe the effect of the longitudinal stresses or we detect the hydrological subglacial networks