Anisotropic behavior of GRIP ices and flow in Central Greenland

Mechanical tests have been performed on strongly textured ice samples coming from a wide range of depths (from 1328 down to 2868 m) of the GReenland Ice core Project (GRIP) for different sample orientations with respect to the prescribed stress. In this way, two directional viscosities, corresponding to the “easy glide” and to the “hard glide” orientations, were determined along the core. The viscoplastic anisotropy gradually increases down to a depth of ∼2600 m and slightly decreases below, revealing a clear correlation between rheology and texture. The experimental mechanical response compares well with that predicted by the ViscoPlastic Self-Consistent (VPSC) model. The VPSC model is also applied to ice samples that exhibit an axisymmetric texture to show in more detail the sensitivity of the rheology to specific texture parameters. This leads to a number of recommendations for future mechanical tests on anisotropic samples. A large-scale ice flow model is finally used to estimate the influence of ice anisotropy on the flow along the GRIP–GISP2 flow line. The particular mechanical behavior of deep GRIP ices in the stress regime corresponding to an ice divide leads to deformation rates that are highly sensitive to bedrock topography and texture pattern. This feature is likely to favour the formation of stratigraphic disturbances in deep ice layers, as observed in the last 300 m of both GRIP and GISP2 cores.