Topographic control on ice anisotropy in Antarctic ice rises inferred from phase-sensitive radar

Marie-Axelle Gillain , Frank Pattyn, Carlos Martin

The Raymond effect within ice rises and underneath ice divides of ice sheets arises from the non-linear rheology of the ice and steady-flow conditions. The resulting Raymond arches seen in radargrams have been associated with crystal orientation fabric (COF) that produces ice optical anisotropy, detectable with radar. We use data collected with a phase-sensitive radar across two ice rises, Hammarryggen and Lokeryggen, both located in Dronning Maud Land, East Antarctica. Despite their proximity, Raymond arches are observed at Hammarryggen but are absent at Lokeryggen. The absence of Raymond arches does not necessarily arise from non-steady conditions close to the bed, but may be controlled by the more complex bedrock topography that reduces ice anisotropy and resulting ice stiffening.