Ice Sheet & Glacier Dynamics
Programme Background
The new satellite observations of the Earth s ice sheets, ice caps and glaciers are immediately applicable to a wide range of cryospheric problems. CPOM will use these to determine directly the mass imbalance of the Antarctic and Greenland Ice Sheets and smaller ice caps and glaciers. A more accurate determination is required to understand 20th and 21st sea level rise, and to unravel the interactions of Holocene ice distribution, post-glacial rebound, sea level rise and Earth rotation. In combination with ground observations, CPOM will use satellite-derived surface velocities as boundary conditions in numerical models of ice dynamics to attack a range of problems. These include the role of ice streams (which are presently absent from models of entire ice sheet evolution) in basin dynamics and near-future sea level evolution, the thermal evolution of the Antarctic ice sheet bed, and related high latitude environmental problems, such as the issue of ancient microbial life in the subglacial Lake Vostok.
The southern Greenland Ice Sheet and Arctic sub-polar ice masses will respond rapidly to climate warming, providing a net contribution to sea level rise due to increased ablation rates at the surface. Increased surface melting will modify snow consolidation, affect melt water run off, and change the scattering and absorption characteristics, altering the spectrally-averaged albedo of the snow. Surface melting also has dynamic implications: as melt water percolates through cracks, it freezes, narrowing the cracks, increasing the thermal inertia of the ice cover, and releasing latent heat which contributes significantly to the thermally-activated, slow flow of ice. Correlations between surface and basal drainage, and surging behaviour are likely to strengthen. These processes introduce new parameterisation problems into the modelling of ice flow which will be addressed through consideration of the snow cover water fraction, and the reaction of the ice sheet to melt water percolation and redistribution of sensible and latent heat. CPOM will develop modelling approaches to these processes, using the specific contexts of the ice caps of the Russian, Norwegian and Canadian Arctic which, because of their relatively small thickness and higher accumulation, have more rapid response times than the great ice sheets.
The ice-sheet modelling expertise which we will develop is also applicable to modelling the climatically-forced behaviour of former ice sheets, in conjunction with palaeoceanographers (to whom we will supply time-dependent meltwater- and iceberg-flux data) and Quaternary scientists (whose chronologically-controlled data on ice-sheet extent will be used to test our model reconstructions). Satellite radar interferometry is fundamental to the provision of wide-area ice sheet surface velocity. The interferometric coverage of the ERS satellites has provided a wealth of information on the spatial and temporal fluctuation of the Earth s ice sheets. Exploitation of these data has only just begun. The substantial data volumes require an international pooling of effort and coordinated access to the ESA archive. This is provided by the VECTRA programme (http://vectra.mssl.ucl.ac.uk), co-ordinated by CPOM. CPOM will continue to lead and develop the VECTRA programme.
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