Spatial depth distribution of the subglacial bed and internal layers in the ice around NGRIP, Greenland, derived with airborne RES

Abstract

In 1996 and 1997, an airborne RES survey was flown in the context of the North Greenland Ice Core Project (NGRIP). At 75.10°N and 42.30°W, a deep ice core is being drilled for palaeoclimate studies with the objective to recover an undisturbed Eemian sequence. The present survey was specially designed to determine with high lateral resolution the bed topography and the layering of internal reflectors in the vicinity around the drill site. A total of 19,000 km of profiles were flown yielding a rectangular grid with side lengths of 222 by 210 km on 16 flights. The spacing between two flight tracks is about 10 km for most of the area and about 2.5 km in the center of the grid. Detailed maps of ice thickness and subglacial topography have been produced. Moreover, a data set was acquired that enables an independent stratigraphic control on the ice core record of NGRIP. From the map of subglacial topography and from selected profiles, the bed of NGRIP can be characterized as flat, particularly when compared to the region of GRIP/GISP2. There appears to be no flow disturbances that might have altered the stratigraphic order in the lower part of the ice sheet, at least up to 30 km upstream from NGRIP. On the basis of the present study, NGRIP seems to be an ideally chosen drill site in order to recover an undisturbed Eemian sequence.