Microstructures in the EPICA DML ice core, Antarctica - sub-grain boundary statistics

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Hamann, I. , Kipfstuhl, S. , Faria, S. H. and Freitag, J. (2007): Microstructures in the EPICA DML ice core, Antarctica - sub-grain boundary statistics , The 2nd International Workshop on Physics of Ice Core Records (PICR-2), February 2 6, 2007, Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan. .
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Various processes on atomic scale (e.g. dislocation climb and glide, diffusionalprocesses etc.) are often competing during flow and deformation of ice sheets. Asthese processes are acting on the atomic scale, they are difficult to observe directlyin deformed polycrystalline ice. However, they leave behind certain structures on themicroscopic scale indicating deformation mechanisms.The microstructure mapping method enables detailed observation and recording ofmany kinds of microstructures (Fig.1) such as grain boundaries, sub-grainboundaries, slip lines and any kind of visible inclusions as air bubbles, air hydrates orparticles (tephra, dust or salt). Data on grain size, sub-grain boundary occurrence,grain elongation and grain shape have been obtained with this method.Mean grain size is increasing with depth mainly in the lower 1500 m. Mean sub-grainboundary density varies between ca. 1 to 2 mm-1 along the length of the core, butdoes not show a distinct depth region of increased sub-grain boundary formation.Mean grain aspect ratio reveals values between ca. 1.7 to 2, though apart from adistinct maximum of ca. 2.3 at 2400 m depth it does not show significant trends.

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