AIR CONTENT ALONG THE GREENLAND ICE CORE PROJECT CORE - A RECORD OF SURFACE CLIMATIC PARAMETERS AND ELEVATION IN CENTRAL GREENLAND

We present here measurements of the air content of the ice, V, perform ed along the Greenland Ice Core Project (GRIP) ice core. The main feat ures of the longterm trends are (1) a decrease of 13% between the last glacial maximum (LGM) and the earliest part of the Holocene, and (2) an increase of 8% during the Holocene. The results are discussed in te rms of changes in atmospheric pressure, surface elevation and porosity at close-off. The V record contains a significant signal of past chan ges of surface elevation in qualitative agreement with ice sheet model ing simulations. It suggests a thickening of central Greenland during the transition from the LGM to the early Holocene, and a significant t hinning through the Holocene period. It also stresses the large influe nce on past V variations of changes in ice porosity, which are not exp lained by the present-day spatial relationship with temperature and ma y reflect changes in other surface climatic parameters (like precipita tion seasonality or wind stress). The potential role of temporal varia tions of atmospheric pressure patterns is also evaluated. Air content results in the GRIP ice older than 110 ka indicate values approximatel y in the same range as those observed during the last 40,000 years, wi th generally higher air content corresponding to isotopically warmer i ce.