Dynamic of the Antarctic Ice Sheet Surface
Vasiliev, Leonid; Kotlyakov, V.M.; Kachalin, A.B.; Moskalevsky, M.Y.; Tyuflin, A.S.
Institute of Geography RAS, RUSSIAN FEDERATION
This paper describes one of the most rapidly developing fields: a holistic approach which is required to place data into the global picture and vice versa for the applicability of models. We outline this concept focussing on particular application of this theory to ice velocity network. Satellite laser altimetry from ICESat made progress in understanding space-time fluctuations of the Antarctic ice sheet surface. However the origin of these fluctuations still remains not clear enough. Now it is possible to study interrelation between ice velocity and surface fluctuation. Physical strength affects ice movement and surface deformation. Analysis of the interferometric ice velocity data over entire Antarctica that were collected by satellites such as ESA’s Envisat, the Canadian Radarsat and Japan Aerospace Exploration Agency ALOS is described. We found further evidence for identification ice velocity network as holistic system. This network has been shown to have distribution that follows power law. The value of the exponent is about 0.85. Such networks are referred to as scale free. The paper provides phenomenological and experimental arguments that ice sheet surface fluctuation in Antarctica is mediated by ice velocity and subglacial water flow. To describe continuum mechanics framework concerning with motion and deformation of body consisting of large number of elements repeat elevation profiles from ICESat have been used. To understand this link we use spatial coherence to refer to the comparison between vertical profile and a shifted profile along the repeat ICESat track. A profile shift due to ice velocity is determined from cross-correlation between initial and shifted profiles. Ice velocity induced fluctuation in surface elevation and deformation of the vertical profile. The cross-correlation between profiles at different time is used to find how much initial profile is shifted along the repeated track. Of particular importance is the water flow beneath the ice sheet and over the cascades of subglacial lakes. It generates irregular rise and fall of the surface. Observation in area of Dome A and its slope have revealed such behaviour of surface, where the surface is placid and ice velocity is measly 2-5 m/y. The surface sank about 30 centimetres during a 3 month period. In the same time interval, a part of the ice sheet downstream rose about 50 centimetres. That change reflects a surge of water. A precise analysis of subglacial water spreading may perhaps lead to a rigorous understanding of the details of percolation. The temporal coherence delay of elevation profiles is quantified by the cross-correlation function. Partial coherence characterizes a degree of coherence and therefore may be considered as a degree of surface deformation. Ice velocity was estimated during subsequent ICESat campaign spanning 2003-2008 years. There are the close dependence of elevation variation and ice velocity. The elevation changes vary considerably according to the elevation amplitudes. The dynamic of the ice sheet epitomizes much of Philip Anderson's classic essay ''More is different''.