Geometric boundary conditions for modelling the velocity field of the Antarctic ice sheet

phuybrechts [ at ]


A comparison of the two-dimensional horizontal velocity field obtained on the basis of conservation of mass (balance velocity) with the diagnostic velocityfield calculated with an ice sheet model (dynamics velocity) may yield information on shortcomings in the way the ice sheet model describes the ice flow. Thispaper presents improved geometric boundary conditions (surface elevation and ice thickness) required as input in such calculations. In particular, the surfaceelevation grid is described in detail, as it has been generated specifically for such a study and represents a new standard in accuracy and resolution forcalculating surface slopes. The digital elevation model was generated on a 10 km grid size from over 20,000,000 height estimates obtained from seven 35-dayrepeat cycles of ERS-1 radar altimeter data. For surface slopes less than 0.5¡ the relative elevation accuracy is better than 1 m. In areas of high surface slope(coastal and mountainous regions) the altimeter measurements have been supplemented with data taken from the Antarctic Digital Database. South of 81.5¡,data from the SPRI folio map have been used. The ice thickness grid was produced from a combination of a re-digitisation of the SPRI folio and the originalradio echo sounding flight lines. For areas of grounded ice, the bedrock was estimated from surface elevation and ice thickness. Significant differences (inexcess of 25 percent of ice thickness) were obtained between an earlier digitisation of the folio bedrock map and the dataset derived here. Furthermore, a newvalue of 26.6 x 106 km3 was obtained for the total volume of the ice sheet and shelves, which is a reduction of 12 percent compared with the original estimatederived during the compilation of the SPRI folio. These differences will have an important influence on the results obtained by numerical ice sheet models.

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Bamber, J. L. and Huybrechts, P. (1996): Geometric boundary conditions for modelling the velocity field of the Antarctic ice sheet , Annals of Glaciology, 23 , pp. 364-373 .

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