Basal melt at NorthGRIP modeled from borehole, ice-core and radio-echo sounder observations 

Annals of Glaciology, Vol. 37, p. 207-212, 2003 

D. Dahl-Jensen and N. Gundestrup
Geofysisk Afdeling, Niels Bohr Instituttet for Astronomi, Fysik og Geofysik, Københavns Universitet
P. Gogineni
Radar Systems and Remote Sensing Laboratory, University of Kansas, 2335 Irving Hill Road, Lawrence, KS 66045-7612, USA.
H. Miller
Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, D-27568 Bremerhaven, Germany.

ABSTRACT.
From temperature measurements down through the 3001 m deep borehole at the North Greenland Icecore Project (NorthGRIP) drill site, it is now clear that the ice at the base, 3080 m below the surface, is at the pressure-melting point, This is supported by the measurements on the ice core where the annual-layer thicknesses show there is bottom melting at the site and upstream from the borehole. Surface velocity measurements, internal radio-echo layers, borehole and ice-core data are used to constrain a time-dependent flow model simulating flow along the north-northwest-trending ice-ridge flowline, leading to the NorthGRIP site. Also time-dependent melt rates along the flowline are calculated with a heat-flow model. The results show the geothermal heat flow varies from 50 to 200 mW m^-2 along the 100 km section of the modeled flowline. The melt rate at the NorthGRIP site is 0.75 cm a^-1, but the deep ice in the NorthGRIP core originated 50 km upstream and has experienced melt rates as high as 1.1 cm a^-1.