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Ice is one of the most anisotropic natural materials but it is common knowledge in our community that anisotropy in ice is: a) a second order factor that can be ignored, b) easily assimilated into isotropic models by tuning certain parameters, or c) so complicated that it is better to ignore. Interestingly, any measurement of anisotropy in polar ice shows that ice develops crystalline preferred-orientation fabrics that produce strong mechanical, optical and dielectric anisotropic properties. Here, we look in detail at polarimetric radar measurements in different regions of East and West Antarctica. We use a ground-based phase-sensitive frequency-modulated continuous-wave radar (ApRES) and a matrix-based model to study the radio-waves depolarization and anisotropic scattering (Fujita et al, 2006). We find that anisotropy is widespread and an excellent archive of past ice flow conditions. We use it here to extract details of the recent deglaciation of the Ross and Ronny ice shelves over the last thousands of years. Also, because the length of the record is related to the advection time of the ice flow, we use our method to show that a candidate ice core location near Dome C, for the Beyond Epica Oldest Ice Core project, has been under steady ice-flow conditions over the last million years or so. [ABSTRACT FROM AUTHOR]

Acoustic impedance is a measurable quantity that can be recovered using active seismic surveys. Its value depends on the speed of sound in the sediment and the sediment density. For granular sediments there are theories that relate the speed of sound to the effective pressure, the difference between ice overburden and subglacial water pressure. This provides a link between the seismic observable and a key control on basal sliding. For sediments that follow a Coulomb friction law, the higher the effective pressure the higher the shear stress supported by the sediments. In this presentation we investigate the links between acoustic impedance, effective pressure and basal drag that are predicted by theories of the speed of sound in granular materials. We use results for basal drag from an ice flow model inversion in Antarctica to predict how acoustic impedance would vary under the hypothesis that sliding is controlled by a Coulomb sliding law. [ABSTRACT FROM AUTHOR]