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, performed along the Greenland Ice Core Project (GRIP) ice core. The main features 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 terms of changes in atmospheric pressure, surface elevation and porosity at close-off. The V record contains a significant signal of past changes of surface elevation in qualitative agreement with ice sheet modeling simulations. It suggests a thickening of central Greenland during the transition from the LGM to the early Holocene, and a significant thinning through the Holocene period. It also stresses the large influence on past V variations of changes in ice porosity, which are not explained by the present-day spatial relationship with temperature and may reflect changes in other surface climatic parameters (like precipitation seasonality or wind stress). The potential role of temporal variations of atmospheric pressure patterns is also evaluated. Air content results in the GRIP ice older than 110 ka indicate values approximately in the same range as those observed during the last 40,000 years, with generally higher air content corresponding to isotopically warmer ice.