Beschreibung:
<jats:p>A digital elevation model (DEM) of the surface of the Antarctic ice sheet is
compared with a simple two-dimensional ice-flow model to illuminate gross
distortions (&gt;500 m) of the ice-surface elevation. We use a DEM derived
from ERS-1 satellite altimetry, airborne data and TWERLE balloon data. This is
compared with an ice-sheet elevation model generated by applying theoretical
surface elevations, calculated for two-dimensional ice flow, to isolines of
distance from the grounding line (continentality). The model is scaled using only
one parameter, to match the measured surface elevation at Dome Argus. The model is
far from rigorous, violating continuity conditions, ignoring variations in surface
mass balance and temperature, and assuming uniform basal conditions. However, the
comparison of model and observed surface elevations is illuminating in terms of
the behaviour of the ice sheet at a continental scale. Across the ice sheet the
rms difference between modelled elevation and the DEM is around 300 m, but much of
this results from isolated areas of much greater disagreement. We ascribe these
gross differences to the effects of basal conditions. in four areas, the observed
surface is more than 500 m higher than the modelled surface. Most of these are
immediately upstream of substantial areas of rock outcrop and are caused by the
damming effect of these mountain ranges. in nine areas, the measured surface is
more than 500 m lower than predicted. Eight of these areas, in West Antarctica and
the Lambert Glacier basin, are associated with suspected areas of basal sliding.
The ninth is an area of 250 000 km<jats:sup>2</jats:sup> in East Antarctica not
previously noted as having unusual flow characteristics, but for which very
few-data exist. We speculate that this area results from unusual basal conditions
resulting in a low-profile ice sheet. A low-profile ice sheet of this size with in
the East Antarctic ice sheet indicates that basal conditions are perhaps more
variable than previously thought.</jats:p>