Unifying and comparing different models of viscous anisotropy to be included in ice sheet models.

Ice fabrics – the alignment of crystal orientations - can cause the ice viscosity to vary by an order of magnitude, consequently having a strong impact on the large-scale flow of ice sheets and glaciers. Because of this, there is a need for fabric models which are computationally efficient enough to be included in large-scale ice sheet models. We examine a range of existing models in this class and show they can be combined into a common equation which is a function of 2-3 parameters. By comparing with observations from the Greenland ice sheet, we get the best model predictions by assuming the ice deforms close to the Sachs hypothesis – that all grains experience the same stress. As these fabric predictions also depend on the flow law used, we provide a test of competing anisotropic flow laws for the first time, making a step towards reliably incorporating the effect of fabric and viscous anisotropy in ice sheet flow models.