Radar Characterization of Ice Crystal Orientation Fabric and Anisotropic Viscosity Within an Antarctic Ice Stream

Abstract

The flow of glacier ice is controlled by its rheology, which determines how ice deforms under an applied stress. A range of rheological factors influence the effective viscosity of ice, including temperature, microstructural properties, such as ice crystal orientation fabric and grain size, damage to the ice, and the character of the underlying stress regime (Cuffey & Paterson, 2010). The ice crystal orientation fabric, from herein referred to as "fabric," describes the orientation distribution of ice crystals in relation to their crystallographic axes (c-axes). The ice fabric is the primary control on anisotropic viscosity (i.e., when the viscosity of ice is softer or harder for different stress components). In addition to influencing present-day deformation, the ice fabric encodes strain history due to the rotation of the c-axes toward the compressive strain axis (direction of least extension) (Azuma

Seismic Noise Interferometry and Distributed Acoustic Sensing (DAS): Inverting for the Firn Layer S‐Velocity Structure on Rutford Ice Stream, Antarctica

“…But within that uncertainty, our measurements are consistent with the Jordan et al. (2022) results and preclude strong azimuthal anisotropy at the center of the ice stream.…”

“…These seismic experiments do not provide constraints on the depth distribution of the anisotropic ice, as the measurements integrate over the entire wave path from the icequake hypocenter at the ice-bed interface to the surface receivers. However, using polarimetric radar measurements, Jordan et al (2022) report near-surface azimuthal anisotropy on Rutford Ice Stream, although their measurements are not coincident with this experiment.…”

“…However, polarimetric radar measurements of Jordan et al. (2022) indicate azimuthal anisotropy at depths of 40–100 m across Rutford Ice Stream. Laterally, they find weaker anisotropy in the ice stream center (less deformation) than toward the shear margin.…”

Crystal fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream

“…Radio-Echo-Sounding (RES) surveys are widely used in glaciology for mapping ice thicknesses, basal properties and internal stratigraphy [19,20,21,22]. Horizontal anisotropy modulates RES signals [23,24] and techniques have recently been developed to derive information on the horizontal component of the COF from RES [25,26,27,28]. The uniaxial birefringent property of ice crystals leads to slightly different velocities of radar waves depending on the wave polarization relative to the preferred orientation of the c-axes.…”

“…Our results show a spatially variable fabric anisotropy that considerably affects the ice stiffness depending on the deformation mechanism and direction. While previous studies [25,26,28] have used similar methods to infer the COF anisotropy of ice streams, the extensive spatial coverage and high resolution of our results as well as the comparison among different methods presented here is unprecedented.…”