Lattice distortion in ice crystals from the Vostok core (Antarctica) revealed by hard X-ray diffraction; implication in the deformation of ice at low stresses

Hard X-ray diffraction experiments have been carried out on ice monocrystals taken from the 3623 m long Vostok core (Antarctica). Strain gradients associated with the storage of geometrically necessary dislocations appear to be a general feature of the deformation microstructure of ice. The observed lattice distortion is related to the bending of the basal plane and the torsion of the lattice around the c-axis. The lattice distortion is shown to be compatible with the basal dislocations generally observed in ice crystals, supporting the assumption of deformation modes governed by basal slip and accommodated by recrystallization processes. The dependence of the ice viscosity on grain size in ice sheets appears to be compatible with these accommodation modes.