Mass balance of the Greenland ice sheet at high elevations

Comparison of ice discharge from higher elevation areas of the entire Green land Ice Sheet with total snow accumulation gives estimates of ice thickeni ng rates over the past few decades. On average, the region has been in bala nce, but with thickening of 21 centimeters per year in the southwest and th inning of 30 centimeters per year in the southeast. The north of the ice sh eet shows Less variability, with average thickening of 2 centimeters per ye ar in the northeast and thinning of about 5 centimeters per year in the nor thwest. These results agree well with those from repeated altimeter surveys , except in the extreme south, where we find substantially higher rates of both thickening and thinning.