Fabric-induced flow enhancement of the Amery ice shelf inferred from satellite-derived surface velocities

During the gravity-driven flow and spreading of ice shelves, polycrystalline ice tends to develop a strain-induced alignment of individual grains. This fabric development can exert significant rheological control on ice shelves, potentially softening or hardening anisotropic ice by several orders of magnitude compared to isotropic ice. We develop a new way to directly solve for depth-average fabric fields using satellite-derived velocities over ice shelves, assuming that velocities are approximately steady and that fabric evolution is dominated by lattice rotation, in a depth-averaged sense. We apply the method to Amery ice shelf, Antarctica, and compare results to previous observations of ice fabrics. Further, we calculate the equivalent isotropic enhancement-factor field using the “CAFFE” method, supposed to represent the first-order effect of fabric on ice viscosity. Because a significant fraction of the ice-shelf thickness on Amery is accreted marine ice, we explore how this may alter the depth-averaged estimate of fabric, and thus viscosity, by including an idealized source term to account for the sub-shelf flux of new grain orientations as ice accretes.