ALBERT

Description: EBSD provides information for the characterization of subgrain boundary types and dislocation activity during deformation. EBSD microstructure in combination with light microscopy measurements from ice core material from Antarctica (EPICA-DML deep ice core) and Greenland (NEEM deep ice core) are presented and interpreted regarding substructure identification and characterization. Electron backscattered diffraction (EBSD) analyses suggest that a large portion of edge dislocations with slip systems basal 〈a〉 gliding on the basal plane were involved in forming subgrain boundaries. However, an almost equal number of tilt subgrain boundaries developed, involving dislocations gliding on non basal planes (prism 〈c〉 or prism 〈c+a〉 slip). A few subgrain boundaries involving prism 〈a〉 edge dislocation glide, as well as boundaries involving basal 〈a〉 twist dislocations, were also identified. The finding that subgrain boundaries occur, made up of dislocations gliding on non-basal planes, are as frequent as basal plane slip systems, is surprising. These findings are expected to have an impact on the discussion of rate-controlling processes for the ice flow descriptions of large ice masses with respect to sea-level evolution. For subgrain boundaries not related to the crystallography of the host grain alternative formation processes are discussed.