Microstructural analysis of the NEEM ice core, Greenland by using electron backscatter diffraction (EBSD)

Mass loss of the Greenland ice sheet is accelerating, which is attributed to increased ice stream discharge and changes in surface mass balance including increased runoff. Ice stream discharge is caused by both ice deformation and basal sliding. For a better projection of future mass loss, it is important to understand deformation mechanisms of polycrystalline ice in ice sheet. Deformation properties of polycrystalline material are related to its microstructure (e.g. crystal grain orientation and size). As recrystallization and recovery are occurring together in ice sheet, microstructural analysis of ice is essential. Electron backscatter diffraction (EBSD) is a method for measuring crystal lattice orientation with high angular and spatial resolutions. Both c- and a-axes of ice can be measured. We analyzed Greenland NEEM ice core and the preliminary result shows that most subgrain boundaries (SGBs) observed by optical microscopy have lattice misorientations < 4°. This result is in accordance with analyses of Antarctic EDML ice core by X-ray diffractometry while it differs from threshold angle of SGB/GB estimated with a dislocation theory. The observation results from ice sheet ice could contribute to better estimations of strain rate by models based on microstructural processes.