Ice-sheet thickening or thinning rates in Antarctica are measured using the
“coffee-can” or “submergence velocity” method. in this, repeated measurements of
the positions of firn anchors are obtained using the global positioning system
(GPS). The thickness change is (lie difference between vertical velocity so
obtained and long-term rate of snow accumulation. Minor corrections for firn
settling and downslopc motion are made. The technique avoids difficulties of
short-term fluctuations in snowfall or snow den-sification. The result for Byrd
Station is near balance, -0.004 (0.022) ma−1, and for the
Dragon, just outboard of Ice Stream B, thinning at -0.096 (0.044)
ma−1. Uncertainties with these first results are mainly
due to the short occupation times during the first GPS surveys.