Large-scale englacial folding and deep-ice stratigraphy within the West Antarctic Ice Sheet

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, 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, representative of ice with a strong preferred crystal 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.

Englacial Architecture and Age‐Depth Constraints Across the West Antarctic Ice Sheet

“…Close to the ice divide,~800 m of ice exists below the 17.5 ka IRH (Jacobel & Welch, 2005; Figures 3e and 3f). Both the 17.5 and 16 ka (after Siegert & Payne, 2004) IRHs are broadly associated with a diffuse region of reflectivity several 100 m thick within IMIS (Ross et al, 2019). Tracing this diffuse zone would further elucidate where thick deposits of ice older than~17.5 ka exist within IMIS.…”

“…flow and ice anisotropy, such as that exemplified by Bons et al (2016) at the onset of Greenland's Petermann Glacier. IMIS is known to have a complex flow history and packages of basal ice with distinct rheology (Bingham et al, 2015;Ross et al, 2019).…”

Automated detection and characterization of Antarctic basal units using radar sounding data: demonstration in Institute Ice Stream, West Antarctica

“…Here, we focus specifically on the potential basal unit in Institute Ice Stream, which has been noted elsewhere by Bingham and others (2015), Winter and others (2015) and Ross and others (2019). The radar echo character of an ice-sheet component – that is, the manner in which it interacts with transmitted radar pulses – is an expression of its wavelength-scale geometry (Campbell, 2007; Grima and others, 2014b).…”

“…These structures are viewed in cross-section, with structure 1 ~ 300 m in height and structure 2 between 100 and 150 m thick. Ross and others (2019) have discussed both of these features in detail. (b) Flight lines (transects) of the British Antarctic Survey's study of Institute and Möller ice streams, West Antarctica.…”

“…A yellow circle denotes the approximate intersection point of the two structures with transect C31a, near 82°S, 77°W. (Both structures stretch over several transects parallel to C31a, and Ross and others (2019) provide a complete mapping.) The grounding line, based on data from the National Snow & Ice Data Center (Bindschadler, 2011), is traced in purple and shading is based on BEDMAP2 surface elevation (Fretwell and others, 2013).…”