Abstract
Abstract. It has been hypothesized that complex englacial structures identified within the East Antarctic and Greenland ice sheets are generated by (i) water freezing to the ice sheet base and evolving under ice flow, (ii) deformation of ice of varying rheology, or (iii) entrainment of basal material. Using ice-penetrating radar, we identify a widespread complex of deep-ice facies in West Antarctica that exist in the absence of basal water. These deep-ice units are extensive, thick (>500 m), and incorporate multiple highly reflective englacial layers. At the lateral margin of an enhanced flow tributary of the Institute Ice Stream, these units are heavily deformed and folded by the action of lateral flow convergence. Radar reflectivity analysis demonstrates that the uppermost reflector of the deep-ice package is highly anisotropic, due to abrupt alternations in crystal orientation fabric, and consequently will have a different rheology to the ice above and below it. Deformation and folding of the deep-ice package is an englacial response to the combination of laterally-convergent ice flow and the physical properties of the ice column.
Highlights
Recent advances in radar technology have enhanced the quality and resolution of ice-penetrating radar data, revealing complex structures in the lower ice sheet column
These have been interpreted as the product of the accretion of basal water (Bell et al, 2011), deformation caused by varying rheology of the ice column (NEEM community members, 2013; Bons et al, 2016), or a combination of both (Bell et al, 2014; Wrona et al, 2018)
At least one layer in the deep ice has physical properties that are significantly different to the upper ice column
Summary
Recent advances in radar technology have enhanced the quality and resolution of ice-penetrating radar data, revealing complex structures in the lower ice sheet column. Thick deep-ice units have been imaged above the Gamburtsev Mountains in East Antarctica (Bell et al, 2011; Wrona et al, 2018), whilst in Greenland units heavily deformed by ice flow have been discovered (NEEM community members, 2013; Bell et al, 2014; Bons et al, 2016) These have been interpreted as the product of the accretion of basal water (Bell et al, 2011), deformation caused by varying rheology of the ice column (NEEM community members, 2013; Bons et al, 2016), or a combination of both (Bell et al, 2014; Wrona et al, 2018). The spatial extent and significance of such fabrics in West Antarctica (and deep-ice units in general) have not been determined
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