Microstructures of natural ice from Northern Victoria Land, Antarctica

Abstract

As polycrystalline ice 1h deforms plastically, it develops an anisotropic, sometimes inhomogeneous by impurity, microstructure, with a strong crystallographic preferred orientation (CPO). As the kinematics and conditions (temperature, stress and strain) of deformation vary, deformed ice exhibits different microstructures. These deformation-induced microstructures of natural ice provide records of the deformation histories and constraints on the future flow rate of natural ice bodies. In order to investigate the formation of microstructures of ice during deformation, we analysed natural ice samples from Styx and Larsen Glaciers, Northern Victoria Land, Antarctica using electron backscatter diffraction (EBSD) technique. The CPOs of ice samples from Styx Glacier (a snow accumulation site) are characterized by single maxima of c-axes with random to girdled distributions of (11-20) and (10-10). The fabric strength progressively increases with increasing depth. The results show the successful formation of ice fabric by the accumulation of ice, indicating that Styx Glacier successively preserve the evidences of paleoclimate. On the other hand, ices from Larsen Glacier (a blue-ice region) display a strong vertical girdle of c-axes with horizontal concentrations of (11-20) and (10-10). This pattern suggests the ice experienced tensile deformation normal to the direction of the c-axes girdle. However satellite data of the sample location in Larsen Glacier imply a weak flow of ice within an error range. Based on those results, we discuss the implications of microstructures in natural ice from Northern Victoria Land, Antarctica.