Ice in the mouth of Ice Stream B, a large glacier in West Antarctica, has slowed by about 20% over a 10 year period. Recent measurements of velocity were made between 1983 and 1988 during the Siple Coast project (SCP) on a 100 km section of ice extending from the ice shelf just up-stream of Crary Ice Rise on to the ice plain of Ice Stream Β (see Fig. 1). They are compared to three velocities measured during the Ross Ice Shelf Geophysical and Glaciological Survey (1973–75). Velocities in both surveys were measured using doppler satellite-tracking methods. The data are given in Table I. Measured strain-rates are used to define a linear strain field which allowed the recent velocities to be extrapolated to the position of the RIGGS measurements. The comparison is given in Table II. The deceleration is above measurement uncertainties, which were estimated at about ±50 m a−1 for the 90% confidence limit. This may be a response to regional thickening down-stream (Reference MacAyeal, Bindschadler, Shabtaie, Stephenson and BentleyMacAyeal and others, 1987) in the region around Crary Ice Rise. Other possible causes include a response to the stagnation of nearby Ice Stream C, changes in basal conditions, or external forcing.
Fig. 1. Ice motion and deformation up-stream of Crary Ice Rise and on the ice plain of Ice Stream B. The thick continuous and broken lines show ice-stream boundaries (after Reference Shabtaie and BentleyShabtaie and Bentley (1987) with modifications). Some of the data in Table I have been omitted for the sake of clarity.
Table I. Observed velocity and strain-rate data
Table II. Comparison of riggs and scp velocities
