Abstract

Complex englacial structures identified within the East Antarctic and Greenland ice sheets are thought to be generated by water freezing to the ice-sheet base, evolving under ice flow. We use ice-penetrating radar to identify and measure complex deep-ice facies in the Weddell Sea sector of West Antarctica, revealing an extensive thick (>500 m) unit, incorporating several unusually highly-reflective, heavily tectonised, folded layers. Radar reflectivity of one layer within the unit is observed to be far greater parallel to flow than orthogonal to it. Such selective englacial anisotropy is most likely explained by an ice layer with a strong and discrete preferred crystal fabric and, consequently, a different rheology. Tectonism and folding associated with the deep-ice layer is a striking rheological response to laterally-convergent ice flow. Similar englacial structures, and therefore rheological controls on ice flow, will likely exist elsewhere in Antarctica and Greenland but current surveys are either too localised, or not optimised, for imaging and characterising them. The classic view of ice flow, governed by a simple and uniform power-law, will not produce such structures. For this reason, the rheology of ice in West Antarctica, and mostly likely other ice masses, should be considered far more complex than previously acknowledged.