DOMINANT INFLUENCE OF ATMOSPHERIC CIRCULATION ON SNOW ACCUMULATION IN GREENLAND OVER THE PAST 18,000 YEARS

PROJECTIONS of sea-level rise due to greenhouse warming often involve the assumption that increased water vapour pressure will enhance snow accumulation in cold regions of ice sheets, partially offsetting the increased melting of low-latitude and low-altitude ice(1-3). To test whether this has been true in the past, we compare accumulation rates(4) and temperatures derived from the oxygen isotope composition(5) of ice in the deep core obtained by the Greenland Ice Sheet Project II (GISP2), We find that atmospheric circulation, not temperature, seems to have been the primary control on snow accumulation in central Greenland over the past 18,000 years. During both warm (Holocene) and cold (Younger Dryas, Last Glacial Maximum) climate regimes, the sensitivity of accumulation to temperature changes is less than expected if accumulation is controlled thermodynamically by the ability of warmer air to deliver more moisture. During transitions between warm and cold climate states, in contrast, accumulation varies more than can be explained in purely thermodynamic terms, probably because of changes in storm tracks, Thus, in a world warmed by the greenhouse effect, circulation changes may be more important than direct temperature effects in determining snow accumulation in Greenland and its contribution to sea-level change.