CALCULATED VARIATIONS OF ANNUAL ICE ABLATION AT THE MARGIN OF THE GREENLAND ICE-SHEET, WEST GREENLAND, 1961-90

Annual ice ablation has been measured at three locations at the margin of the Greenland ice sheet: Nordbogletscher (for 6 years: 1977-78 to 1982-83), Qamanarssup sermia (8 years: 1979-80 to 1986-87) and at Paakitsup Akuliarusersua (7 years: 1982-83 to the present). As the data sets cover different periods, it is difficult to compare ablation directly between the three sites. However, measured series at each site can be extended over the last 30 years (1961-90) by simulations using climatic data, and the extended data series can be compared. The pattern of calculated ablation variations at the three locations is remarkably similar with no sign of any trend towards increased ablation in recent years. There was generally low ablation from the mid-1970s to the mid-1980s that may explain the recent thickening of the ablation area which has been detected by satellite radar altimetry. Ablation varies substantially from year to year, e.g. with a standard deviation of the order of +/-0.5 m water a-1, and any future monitoring programme must detect trends of increasing ablation against this background of natural variations.