Full crystallographic orientation ( c and a axes) of warm, coarse-grained ice in a shear-dominated setting: a case study, Storglaciären, Sweden

• Published in: The Cryosphere
• Main Authors: M. E. Monz, P. J. Hudleston, D. J. Prior, Z. Michels, S. Fan, M. Negrini, P. J. Langhorne, C. Qi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Storglaciären; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-15-303-2021; https://doaj.org/article/0ac1ecc985bb4a21a9aab492ca5c716f

Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice deforms dominantly by dislocation glide on the basal plane, modified and often intensified by dynamic recrystallization. CPO patterns in fine-grained ice have been relatively well characterized and understood in experiments and nature, whereas CPO patterns in “warm” ( <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>T</mi><mo>></mo><mo>-</mo><mn mathvariant="normal">10</mn><mspace width="0.125em" linebreak="nobreak"/><mrow class="unit"><msup><mi/><mo>∘</mo></msup><mi mathvariant="normal">C</mi></mrow></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="d9cfbf6c51510b0b97b2ae848f767c11"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tc-15-303-2021-ie00001.svg" width="54pt" height="11pt" src="tc-15-303-2021-ie00001.png"/></svg:svg> ), coarse-grained, natural ice remain enigmatic. Previous microstructural studies of coarse-grained ice have been limited to c -axis orientations using light optical measurements. We present the first study of a axes as well as c axes in such ice by application of cryo-electron backscatter diffraction (EBSD) and do so in a shear-dominated setting. We have done this by developing a new sample preparation technique of constructing composite sections, to allow us to use EBSD to obtain a representative, bulk CPO on coarse-grained ice. We draw attention to the well-known issue of interlocking grains of complex shape and suggest that a grain sampling bias of large, branching crystals that appear multiple times as island grains in thin sections may result in the typical multimaxima CPOs previously ...