Master Thesis Defense by Laura Lund Rysager

Title: The Evolution of Crystal Orientation Fabric and Ice Flow in Ice Streams

Abstract:
The evolution of grain orientations (henceforth ice fabric) as a function of flow in polycrystalline glacier ice can greatly affect the bulk viscous anisotropy of ice, and hence mass loss from Earth’s large ice sheets through fast-flowing ice streams where such effects are thought to be important. In this thesis, I model the strain-induced evolution of grain orientation of Lagrangian parcels of ice propagating into and through the North-East Greenland Ice Stream (NEGIS) given the local deformation observed from satellite-derived surface strain rate fields. This allows me to estimate the local flow enhancement factors to better understand the relevance of the viscous anisotropy of ice in ice streams. To that end, two different models coupling ice flow and fabric have been experimented with and validated against deformation tests made on ice-core samples before applying the models to the NEGIS region of interest. As the ice 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, I compare the modeled fabric horizontal anisotropy with that inferred from polarimetric radar measurements made near the East Greenland Ice Core Project (EGRIP) drill site.

Supervisor: Nicholas Mossor Rathmann
Censor: Jens Olaf Pepke Pedersen (DTU)