Crystal-orientation fabric variations on the sub-metre scale in cold Alpine ice

• Main Authors: Kerch, Johanna, Weikusat, Ilka, Diez, Anja, Bohleber, Pascal, Eisen, Olaf
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: ice core; The Cryosphere
• Online Access: https://epic.awi.de/id/eprint/45499/; https://hdl.handle.net/10013/epic.51615

The macroscopic flow of a glacier is substantially influenced by the plastic anisotropy of individual ice crystals on the microscale. A preferred crystal orientation fabric (COF) develops with depth in a glacier and is subjected to the influence of the temperature, deformation and recrystallisation regime as well as the climate-dependent impurity load in the ice. Detailed knowledge about the crystal anisotropy in a glacier is thus required to better constrain the response of ice sheets in a changing climate. While the gradual change in anisotropy on a large scale of tens to hundreds of metres can mostly be explained, this is not the case for changes in the anisotropic fabric on a shorter scale of centimetres to decimetres. It is therefore essential to improve the understanding of how and why the anisotropic COF changes on a sub-metre scale in a glacier. Fabric data from an ice core of 72 m length, drilled at the high-altitude Alpine site Colle Gnifetti in Switzerland, were measured in continuously sampled sections of ca. 1 m length, covering 10 % of the entire core length. The eigenvalues of the second-order orientation tensor describing the distribution of crystal axes were analysed in high-resolution together with impurity data from meltwater analysis. It is found that the fabric anisotropy exhibits a strong variability on the short scale in all depths of the ice core with extreme eigenvalue differences within one metre of up to 0.2, often associated with small- or large-grained layers. The observation of a clear connection between the grain size variation and the impurity content leads to the conclusion that the influence of impurities on short-scale fabric variations is partially conveyed by the impurity-controlled grain size in combination with the local deformation regime.