Englacial seismic reflectivity: imaging crystal-orientation fabric in West Antarctica

• Published in: Journal of Glaciology
• Main Authors: Horgan, HJ, Anandakrishnan, S, Alley, RB, Burkett, PG, Peters, LE
• Format: Article in Journal/Newspaper
• Language: English
• Published: Int Glaciol Soc 2011
• Subjects: Earth Sciences; Physical Geography and Environmental Geoscience; Glaciology; Bindschadler Ice Stream; Thwaites Glacier; West Antarctica; Antarc*; Antarctica; Antarctica Journal; Ice Sheet; Journal of Glaciology
• Online Access: https://doi.org/10.3189/002214311797409686; http://ecite.utas.edu.au/103758

Abrupt changes in crystal-orientation fabric (COF), and therefore viscosity, are observednear the base of the ice sheet throughout West Antarctica. We report on active-source seismicobservations from WAIS Divide, mid-stream and downstream on Thwaites Glacier, and the onset regionof Bindschadler Ice Stream. These data reveal a prevalence of englacial seismic reflectivity in the bottomquarter of the ice sheet. The observed seismic reflectivity is complex but largely bed-conformable,with long-spatial-wavelength features observed in the flow direction and short-wavelength featuresobserved across flow. A correspondence of englacial structures with bed features is also observed. Wedetermine the origin of the reflectivity to be abrupt changes in the COF of ice, based on the following:(1) observations of englacial reflectivity are consistent with current knowledge of COF within ice sheets,(2) englacial reflectivity caused by COF contrasts requires the simplest genesis, especially at ice divides,and (3) amplitude analysis shows that the observed englacial reflectivity can be explained by contrastsin seismic velocity due to COF changes. We note that the downstream increase in the quantity andcomplexity of observations indicates that direct observations of COF at ice divides likely underestimatethe role that fabric plays in ice-sheet dynamics.