MASS-BALANCE AND SURFACE MOVEMENT OF THE GREENLAND ICE-SHEET AT SUMMIT, CENTRAL GREENLAND

During the GRIP deep drilling in Central Greenland, the ice sheet topo graphy and surface movement at Summit has been mapped with GPS. Measur ements of the surface velocity are presented for a strain net consisti ng of 13 poles at distances of 25-60 km from the GRIP site. Some resul ts are: The GRIP site is located approximately 2 km NW of the topograp hic summit; the surface velocity at the GISP 2 site is 1.7 m/yr in the W direction. The present mass balance at Summit is calculated to be - 0.03+/-0.04 m/yr, i.e. close to steady state. This result is the best now available for Summit. A small thinning rate might be a transient r esponse of the Greenland Ice Sheet due to the temperature increase at the Wisconsin-Holocene transition.