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


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johanna.kerch [ at ] awi.de

Abstract

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.



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Conference (Talk)
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Primary Division
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Not peer-reviewed
Publication Status
Published
Event Details
International Symposium on the Cryosphere in a Changing Climate, 12 Feb 2017 - 17 Feb 2017, Wellington, Neuseeland.
Eprint ID
45499
Cite as
Kerch, J. , Weikusat, I. , Diez, A. , Bohleber, P. and Eisen, O. (2017): Crystal-orientation fabric variations on the sub-metre scale in cold Alpine ice , International Symposium on the Cryosphere in a Changing Climate, Wellington, Neuseeland, 12 February 2017 - 17 February 2017 .


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