SULFATE AND MSA IN THE AIR AND SNOW ON THE GREENLAND ICE-SHEET

Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surf ace snow, and snowpit samples have been measured at two sites on the G reenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the su rface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but t he ratios of the concentrations are comparable. The seasonal variation s for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter and short episodes of elevated concentrations in spring. In contrast, the variations in concentrations of MSA are similar to those measured at s ea level, with a first sequence of elevated concentrations in spring a nd another one during summer, and a winter low resulting from low biog enic production. The ratio MSA/sulfate clearly indicates the influence of high-latitude sources for the summer maximum of MSA, but the large impact of anthropogenic sulfate precludes any conclusion for the spri ng maximum. The seasonal pattern observed for these species in a snowp it sampled according to stratigraphy indicates a deficit in the accumu lation of winter snow at the summit of the Greenland Ice Sheet, in agr eement with some direct observations. A deeper snowpit covering the ye ars 1985-1992 indicates the consistency of the seasonal pattern for MS A over the years, which may be linked to transport and deposition proc esses.