Institute of Earth Sciences University of Iceland Sturlugata 7 IS101 Reykjavik Iceland

Ice in the ice sheets on Earth (ice Ih) has only two independent easy slip systems, both in the basal plane (0001)<1120> (Ashby & Duval, 1985). When ice undergoes ductile deformation, it develops fabric (lattice-preferred orientation) due to intracrys-talline slip (Wenk et al., 1991).The c-axes rotate towards the principal compression axis (Azuma, 1994), in the absence of recrystallization, as qualitatively known from thin-section measurements (Gow et al., 1997; Thorsteinsson et al., 1997), and from sonic-logging measurements in boreholes (Taylor, 1982). Dynamic recrystallization also induces changes in the fabric; then the recrystallized fabric reflects the symmetry of the current stress state, and memory of prior strain history and fabric evolution can be obscured or lost. As a consequence of fabric development, the bulk physical properties become anisotropic.

To model the flow of ice sheets, we must account for the anisotropy. Models of the fabric evolution and deformation of arrays of crystals as they travel along particle paths can characterize fabric over large parts of the ice sheets, where the flow field changes slowly. Where there are rapid changes in the flow field, a fabric-evolution model following a particular path represents the properties of a smaller volume of ice.

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