ICE FLOW BETWEEN THE GREENLAND ICE CORE PROJECT AND GREENLAND ICE-SHEET PROJECT-2 BOREHOLES IN CENTRAL GREENLAND

The ice flow between the Greenland Ice Core Project (GRIP) and Greenla nd Ice Sheet Project 2 (GISP2) boreholes in the Summit region of centr al Greenland is modeled with a steady state finite element model. The model calculates the free ice sheet surface and the coupled ice flow a nd temperature fields along the flow line between the boreholes. Three -dimensional effects are expressed in terms of the divergence of the f low and included in the coupled stress and temperature fields. In addi tion to ice-core data, several geophysical surface programs have provi ded data that are used to constrain the model. The modeled isochrones resemble the bedrock structure along the flow line but rise at the div ide. The rise at the divide is not seen in internal layers found by su rface radio echo sounding. An ice particle, originally deposited at th e surface, moves through different stress and temperature regimes. A s et of trajectory lines are followed from the surface to the boreholes, in order to follow the variation of stress deviators, temperature, an d deformation along with the ice movement. These variations along a tr ajectory line constitute a history of the corresponding ice layer. The difference between the history of ice layers found in the GRIP and GI SP2 boreholes is mainly due to the shear stress, which is 3-4 times hi gher for GISP2 ice than for GRIP ice. Furthermore, the GRIP ice experi ences a nonzero longitudinal stress deviator much longer than the GISP 2 ice.