Inferring ice fabric from birefringence loss in airborne radargrams : application to the eastern shear margin of Thwaites Glacier, West Antarctica

• Published in: Journal of Geophysical Research: Earth Surface
• Main Authors: Young, T. J., Schroeder, D. M., Jordan, T. M., Christoffersen, P., Tulaczyk, S. M., Culberg, R., Bienert, N. L.
• Other Authors: NERC, University of St Andrews.Bell-Edwards Geographic Data Institute, University of St Andrews.School of Geography & Sustainable Development
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Ice penetrating radar; Polarimetry; Antarctica; Birefringence; Fabric; Glaciology; 3rd-DAS; MCC; Antarctic; West Antarctica; Thwaites Glacier; Christoffersen; Antarc*; Antarctica Journal; British Antarctic Survey
• Online Access: https://hdl.handle.net/10023/27405; https://doi.org/10.1029/2020jf006023

Funding: This work is ITGC Contribution No. ITGC-036 and is an output from the Thwaites Interdisciplinary Margin Evolution (TIME) project as part of the International Thwaites Glacier Collaboration (ITGC), supported by Natural Environment Research Council (NERC) research grant #NE/S006788/1 supporting T. J. Young and P. Christoffersen, and National Science Foundation (NSF) research grant #1739027 supporting S. M. Tulaczyk and D. M. Schroeder. Logistics for this project were provided by the NSF-U.S. Antarctic Program and NERC-British Antarctic Survey. R. Culberg is supported by a USA Department of Defense NDSEG Fellowship and N. L. Bienert is supported by an NSF Graduate Research Fellowship. In airborne radargrams, undulating periodic patterns in amplitude that overprint traditional radiostratigraphic layering are occasionally observed, however, they have yet to be analyzed from a geophysical or glaciological perspective. We present evidence supported by theory that these depth-periodic patterns are consistent with a modulation of the received radar power due to the birefringence of polar ice, and therefore indicate the presence of bulk fabric anisotropy. Here, we investigate the periodic component of birefringence-induced radar power recorded in airborne radar data at the eastern shear margin of Thwaites Glacier and quantify the lateral variation in azimuthal fabric strength across this margin. We find the depth variability of birefringence periodicity crossing the shear margin to be a visual expression of its shear state and its development, which appears consistent with present-day ice deformation. The morphology of the birefringent patterns is centered at the location of maximum shear and observed in all cross-margin profiles, consistent with predictions of ice fabric when subjected to simple shear. The englacial fabric appears stronger inside the ice stream than outward of the shear margin. The detection of birefringent periodicity from non-polarimetric radargrams presents a novel use of subsurface radar ...