Seasat Altimeter Observations of an Antarctic “Lake”

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Abstract
The word “lake” in the context of Antarctica has been used to describe both surface features (10–12 km in size) and areas of liquid water on the bedrock beneath the ice sheet (typically a few kilometres in size and at a depth of over 3000 m), There has been however only limited evidence for a relationship between the two phenomena.This paper reports an analysis of Seasat altimeter observations of an extremely flat area on the surface of the East Antarctic ice sheet, approximately 30 km in extent, centred at 68.6°S 136.0°E and close to the edge of the sub-glacial Astrolabe Basin. It has a regional slope of between zero and 0.01° , and non-random variations in height along track of about ± 1m on the scale of a few kilometres. The average radar backscatter coefficient is 5±2 dB in the region of the Astrolabe Basin, compared to a more usual value of about 10 dB for other areas of the ice sheet. A computer enhanced Landsat image of the region clearly shows the rougher steeper terrain to the North, with the surface in and around the flat area appearing totally smooth and featureless.NSF/SPRI/TUD radio echo-sounding data from the region, although limited in extent, shows a relatively strong signal (indicative of ice at the pressure melting point) over a large region. The signal under the flat area, however, is particularly strong and smooth, confirming the association between the surface feature and a bedrock lake 3800 m below.