Crystallographic Preferred Orientation (CPO) Development Governs Strain Weakening in Ice: Insights From High‐Temperature Deformation Experiments

Fan, Suhua; Cross, Andrew; Prior, David J.; Goldsby, D. L.; Hager, Travis F.; Negrini, Marianne; Qi, Chongchong

doi:10.1029/2021jb023173

Cited by 10 publications

(11 citation statements)

References 119 publications

(295 reference statements)

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“…The local deformation rate of glacier ice depends on its effective viscosity, which is predominantly controlled by temperature and the COF, while other factors such as grain size distribution, impurities, and water content play a notable but minor role 36 – 39 . Strong COFs have long been known to change the directional viscosity of ice by several orders of magnitude compared to isotropic ice 40 , 41 .…”

Section: Resultsmentioning

confidence: 99%

Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

et al. 2023

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The dynamic mass loss of ice sheets constitutes one of the biggest uncertainties in projections of ice-sheet evolution. One central, understudied aspect of ice flow is how the bulk orientation of the crystal orientation fabric translates to the mechanical anisotropy of ice. Here we show the spatial distribution of the depth-averaged horizontal anisotropy and corresponding directional flow-enhancement factors covering a large area of the Northeast Greenland Ice Stream onset. Our results are based on airborne and ground-based radar surveys, ice-core observations, and numerical ice-flow modelling. They show a strong spatial variability of the horizontal anisotropy and a rapid crystal reorganisation on the order of hundreds of years coinciding with the ice-stream geometry. Compared to isotropic ice, parts of the ice stream are found to be more than one order of magnitude harder for along-flow extension/compression while the shear margins are potentially softened by a factor of two for horizontal-shear deformation.

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Section: Resultsmentioning

confidence: 99%

Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

et al. 2023

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“…Strain weakening may be accounted for by (a) the alignment of ice basal planes into easy‐slip orientations, and/or (b) widespread recovery and recrystallization, acting to relax strain heterogeneities, minimize dislocation tangles, and produce soft (initially) strain‐free recrystallized grains. In particular, strain‐induced GBM is rapid at temperatures close to the ice melting point, and can promote strain weakening via the preferential growth of grains in easy‐slip orientations (Fan, Cross, et al., 2021). Therefore, mechanical hardening will likely be counteracted by strain‐weakening processes, including crystallographic preferred orientation development and dynamic recrystallization.…”

Section: Discussionmentioning

confidence: 99%

Using Misorientation and Weighted Burgers Vector Statistics to Understand Intragranular Boundary Development and Grain Boundary Formation at High Temperatures

et al. 2022

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During plastic deformation, strain weakening can be achieved, in part, via strain energy reduction associated with intragranular boundary development and grain boundary formation. Grain boundaries (in 2D) are segments between triple junctions, that connect to encircle grains; every boundary segment in the encircling loop has a high (>10°) misorientation angle. Intragranular boundaries terminate within grains or dissect grains, usually containing boundary segments with a low (<10°) misorientation angle. We analyze electron backscatter diffraction (EBSD) data from ice deformed at −30°C (Th≈ ${T}_{h}\approx $ 0.9). Misorientation and weighted Burgers vector (WBV) statistics are calculated along planar intragranular boundaries. Misorientation angles change markedly along each intragranular boundary, linking low‐ (<10°) and high‐angle (10–38°) segments that exhibit distinct misorientation axes and WBV directions. We suggest that these boundaries might be produced by the growth and intersection of individual intragranular boundary segments comprising dislocations with distinct slip systems. There is a fundamental difference between misorientation axis distributions of intragranular boundaries (misorientation axes mostly confined to ice basal plane) and grain boundaries (no preferred misorientation axis). These observations suggest during progressive subgrain rotation, intragranular boundaries remain crystallographically controlled up to large misorientation angles (>>10°). In contrast, the apparent lack of crystallographic control for grain boundaries suggests misorientation axes become randomized, likely due to the activation of additional mechanisms (such as grain boundary sliding) after grain boundary formation, linking boundary segments to encircle a grain. Our findings on ice intragranular boundary development and grain boundary formation may apply more broadly to other rock‐forming minerals (e.g., olivine, quartz).

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“…The local deformation rate of glacier ice depends on its effective viscosity, which is predominantly controlled by temperature and the COF, while other factors such as grain size distribution, impurities, and water content play a notable but minor role [37,38,39,40]. Strong COFs have long been known to change the directional viscosity of ice by several orders of magnitude compared to isotropic ice [41,42].…”

Section: Soft Ice or Hard Ice -A Question Of Fabric Type And Strain O...mentioning

confidence: 99%

Crystal fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

Gerber

Lilien

Rathmann

et al. 2022

Preprint

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The dynamic mass loss of ice sheets due to ice flow constitutes one of the biggest uncertainties in projections of ice-sheet evolution and sea-level rise. One central, understudied aspect of ice flow is how the bulk orientation of the ice-crystal lattice (fabric) translates to the mechanical anisotropy of ice. Here, we present a comprehensive analysis of the depth-averaged fabric distribution and corresponding directional flow enhancement factors covering a large area of the Northeast Greenland Ice Stream onset region. Our results are based on a combination of methods applied to extensive airborne and ground-based radar surveys, ice-core observations, and numerical ice-flow modelling. They show a strong spatial variability of the horizontal fabric anisotropy and a rapid crystal reorganization on the order of hundreds of years coinciding with the ice-stream geometry. The ice in parts of the ice stream is found to be up to one order of magnitude harder for pure-shear deformation in flow direction compared to isotropic ice, while the shear margins are potentially softened for horizontal simple shear by a factor of two. The high spatial resolution and large-scale coverage of our results is unprecedented and significantly contributes towards more accurate ice-flow models and a better understanding of ice-stream dynamics. Moreover, our estimated time scale of crystal reorganization and methodological approaches can potentially also be transferred to the investigation of ice on extraterrestrial bodies and other geologic materials.

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Crystallographic Preferred Orientation (CPO) Development Governs Strain Weakening in Ice: Insights From High‐Temperature Deformation Experiments

Cited by 10 publications

References 119 publications

Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

Using Misorientation and Weighted Burgers Vector Statistics to Understand Intragranular Boundary Development and Grain Boundary Formation at High Temperatures

Crystal fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

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