Deducing Thickness Changes Of An Ice Sheet From Radio-Echo And Other Measurements

Abstract

The displacement of the surface of an ice sheet and of markers set in its top layers can be measured geodetically, and also, it is expected, by radio-echo methods. The paper discusses how such measurements could be interpreted as showing long-term changes in the thickness of the ice sheet; in particular it discusses how one might design an experiment so as to avoid unwanted effects due to short-term changes in rate of accumulation. The analysis is similar to that of Federer and others (1970), but it corrects an error, so that when applied to their results for central Greenland it gives a different result for the lowering of the surface. Federer and others have already concluded that the average accumulation rates during the past 100 years have been below those needed to keep in balance with the velocity of the ice sheet as a whole. Using a particular model, it is found that this has resulted in the surface lowering at a mean rate of 0.050 m a−1 between 1871 and 1968, and a mean rate of 0.140 m a−1 between 1959 and 1968.