Some Aspects of the Flow of the Ronne Ice Shelf

A new ice-thickness map has been compiled for the Ronne Ice Shelf north of about 81 °S using airborne radio-echo data collected by the British Antarctic Survey since 1975. Comprehensive cover was obtained during the 1982/83 season with flight lines at approximately 50 km spacing. The major features described previously are confirmed, but additional information over the western half of the ice shelf where there were few data before, has revealed the strong identity of individual ice streams. Individual features on radio-echo records, such as abrupt changes in echo strength or prominent bottom crevasses, allow flowlines to be drawn over the western part of the ice shelf. These correspond well with surface features seen on Landsat images.Ice-front positions measured by the West German expedition have given a velocity profile between Berkner Island and the Antarctic Pensinsula. The profile can be fitted reasonably well by making a number of simplifying assumptions. In addition, velocities are known at the grounding line of the Rutford Ice Stream and across the ice rumples between Korff and Henry ice rises. Velocity profiles can be deduced along the two relevant flowlines using the principle of mass balance. Detailed results are of course dependent on bottom melting assumptions, but for the Rutford flowline there must be an average of 1 m/yr of bottom ice melt, assuming a net surface accumulation of 0.3 m/yr. Towards the ice front the melt rate probably increases to several meters per year. Calculations suggest that if the retarding force acting along the flowline were to be reduced slightly by, for example, iceberg calving, then the strain rates would show a significant, if temporary, increase. Ice at the grounding line takes about 1000 years to reach the ice front.Along the flowline from the rumples there is probably only a small amount of bottom melting, in the order of 0.1 m/yr. Although over most of its length there is a retarding force, close to the ice front the force becomes tensile. This can be explained by a reversal in sign of the transverse shear stress gradient. This is consistent with the existence of a curvilinear rift in the ice front just to the west of the rumple flowline.