Mass balance of higher-elevation parts of the Greenland ice sheet

Satellite radar and aircraft laser altimeter data and a volume budget comparison of total snow accumulation with total ice discharge give three independent estimates of the recent mass balance of parts of the Greenland ice sheet above similar to2000 m elevation. Results show the entire region, on average, to be in balance to within 10 mm yr(-1), with very low rates of regional thickness change (dH/dt) in the northeast but high rates with large spatial variability in the south. Only the volume budget estimates show significant thinning in the northwest, but thinning in this area is also inferred from local measurements of ice vertical velocities down boreholes. South of latitude 68degreesN, there has been rapid thickening west of the ice divide, with equally rapid thinning in the southeast, but with large differences between the three estimates of dH/dt throughout this region. The radar data apply to the period 1978-1988, the laser data are for 1993/1994-1998/1999, and the volume budget calculations represent conditions over at least the last few decades. Consequently, many of the differences between results could be caused by temporal changes, particularly in snow accumulation rates, that occurred since the 1970s. However, taken with other information, our results suggest long-term thickening in the southwest and possibly quite recent onset of rapid thinning in the southeast.