The coupled evolution of crystal orientation fabric and ice flow in ice streams

The evolution of grain orientations as a function of flow in polycrystalline glacier ice can greatly affect the bulk viscous anisotropy of ice, and hence mass loss from Earths large ice sheets through fast-flowing ice streams where such effects are thought to be important. In this study, we model the strain-induced evolution of grain orientation (fabric) of Lagrangian parcels of ice propagating into, and through, the North-East Greenland Ice Stream (NEGIS) given the local deformation as observed from satellite-derived surface strain rate fields. This allows us to estimate the local flow enhancement factors to be better at understanding the relevance of viscous anisotropy of ice in the ice streams. As the parcels move into and through the ice stream, very different strain-rate regimes are encountered (outside, in the shear margin, and inside the ice stream) which change the fabric over short spatial/temporal scales. To test the model predictions, we compare the modeled fabric eigenvalues with horizontal eigenvalue differences inferred from radar measurements made near the EGRIP drill site.