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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-147
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-147
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Jul 2020

16 Jul 2020

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This preprint is currently under review for the journal TC.

Grounding zone subglacial properties from calibrated active source seismic methods

Huw J. Horgan1, Laurine van Haastrecht1, Richard B. Alley2, Sridhar Anandakrishnan1, Knut Christianson3, and Atsuhiro Muto4 Huw J. Horgan et al.
  • 1Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
  • 2Department of Geosciences and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 3Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA
  • 4Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA

Abstract. The grounding zone of Whillans Ice Stream, West Antarctica, exhibits an abrupt transition in basal properties from the grounded ice to the ocean cavity over distances of less than 0.5–1 km. Active source seismic methods reveal the grounded portion of the ice stream is underlain by a relatively stiff substrate (relatively high shear wave velocities) compared to the deformable till found elsewhere beneath the ice stream. Several kilometers upstream of the grounding zone, layers of subglacial water are detected, as are regions that appear to be water layers less than the thickness resolvable by our technique. The presence of stiff subglacial sediment and thin water layers upstream of the grounding zone supports previous studies that have proposed the dewatering of sediment within the grounding zone and the possibility that ocean water is pumped into the subglacial system and upstream. The setting enables calibration of our methodology using returns from the floating ice shelf. This allows a comparison of different techniques used to estimate the sizes of the seismic sources. We find a strong correlation (coefficient of determination = 0.45) between our calibrated method and a commonly used amplitude ratio method, but our results also highlight the incomplete knowledge of other factors affecting the amplitude of seismic sources and reflections in the cryosphere.

Huw J. Horgan et al.

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Huw J. Horgan et al.

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Latest update: 04 Aug 2020
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Short summary
The grounding zone marks the transition from a grounded ice sheet to a floating ice shelf. Much like our planet's coastlines, the grounding zone is home to interactions between the ocean, fresh water, and geology, but also has added complexity and importance due to the overriding ice. Here we use seismic surveying – sending sound waves down through the ice – to image the grounding zone of Whillans Ice Stream in West Antarctica and learn more about the nature of this important transition zone.
The grounding zone marks the transition from a grounded ice sheet to a floating ice shelf. Much...
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