Master Thesis Defense by Athene Elizabeth Stuart Demuth

Title: Modeling the evolution of crystal orientation fabrics in an Antartic ice shelf

Abstract:
   Antarctic ice shelves response to global warming is a major source to uncertainty on predicted sea level rise. In this thesis project, we will look at how anisotropy of the collective orientation of small ice grains (called \textit{fabric}) can change the physical properties of the Antarctic ice shelf Amery.

    To this end, we need to bridge the gap between grain scale and the large scales of an ice shelf. First of all, we will implement three different methods for the description of fabric evolution. Measurements of fabric has been done for multiple ice cores, and these present us with controlled setups, which allows us to validate the methods.

    Furthermore, two models using different homogenization schemes of the continuum mechanical properties of ice grains will be tested. These will be validated against novel data from the company xnovotech.

    Using one of the setups, we will develop a depth-averaged fabric model of the Amery ice shelf under a steady state shallow shelf assumption. The fabric field will be modeled using a finite element method and use surface velocities from satellites. By implementing a scalar enhancement factor we can compare the fabric-induced hardness of the ice shelf to the assumption of isotropic ice, and we see both regions with hardening and some significant softening of the ice due to anisotropy.

 Antarctic ice shelves response to global warming is a major source to uncertainty on predicted sea level rise. In this thesis project, we will look at how anisotropy of the collective orientation of small ice grains (called \textit{fabric}) can change the physical properties of the Antarctic ice shelf Amery.

    To this end, we need to bridge the gap between grain scale and the large scales of an ice shelf. First of all, we will implement three different methods for the description of fabric evolution. Measurements of fabric has been done for multiple ice cores, and these present us with controlled setups, which allows us to validate the methods.

    Furthermore, two models using different homogenization schemes of the continuum mechanical properties of ice grains will be tested. These will be validated against novel data from the company xnovotech.

    Using one of the setups, we will develop a depth-averaged fabric model of the Amery ice shelf under a steady state shallow shelf assumption. The fabric field will be modeled using a finite element method and use surface velocities from satellites. By implementing a scalar enhancement factor we can compare the fabric-induced hardness of the ice shelf to the assumption of isotropic ice, and we see both regions with hardening and some significant softening of the ice due to anisotropy.

Supervisors: Nicholas Rathmann, Aslak Grinsted
Censor: Jens Olaf Pepke Petersen, DTU Space