Stability and Uncertainty of Ice-Sheet Crystal Fabrics

Abstract

Ice crystal orientation fabric has a large effect on polycrystalline ice flow. In this thesis, I explore uncertainty of ice fabric measurements, and the related question of stability of ice crystal fabrics and anisotropic ice flow in ice sheets. I develop new estimates of uncertainty of fabric parameter estimates from thin-section data, and connect this to uncertainty in ice flow characteristics. To reduce this sampling error, I develop a new inverse method to infer fabric parameters from sonic velocity measurements and thin-section samples. I show a number of results concerning the stability of ice crystal fabrics in ice sheets. First, I show that small velocity gradient perturbations can induce large changes in ice fabric, which in turn affects anisotropic ice viscosity significantly. Next, I analyze the development of incipient fabric perturbations in coupled flow. I develop an analytical coupled model of anisotropic ice flow and fabric evolution, and show that the coupled system is unstable in many circumstances under ice-sheet flank flow and divide flow.