20 Jan 2021

20 Jan 2021

Review status: this preprint is currently under review for the journal TC.

Polarimetric radar reveals the spatial distribution of ice fabric at domes in East Antarctica

M. Reza Ershadi1, Reinhard Drews1, Carlos Martín2, Olaf Eisen3,5, Catherine Ritz4, Hugh Corr2, Julia Christmann3,6, Ole Zeising3,5, Angelika Humbert3,5, and Robert Mulvaney2 M. Reza Ershadi et al.
  • 1Department of Geosciences, University of Tübingen, Tübingen, Germany
  • 2British Antarctic Survey, Natural Environment Research Council, Cambridge, UK
  • 3Alfred Wegener Institute Helmholtz-Centre for Polar- and Marine Research, Bremerhaven, Germany
  • 4University Grenoble Alpes, CNRS, IRD, IGE, Grenoble, France
  • 5Department of Geosciences, University of Bremen, Bremen, Germany
  • 6Institute of Applied Mechanics, University of Kaiserslautern, Germany

Abstract. Ice crystals are mechanically and dielectrically anisotropic. They progressively align under cumulative deformation, forming an ice crystal orientation fabric that, in turn, impacts ice deformation. However, almost all the observations of fabric are from ice core analysis and its interplay with the flow is unclear. Here, we present a non-linear inverse approach that combines radar polarimetry with vertical changes in anisotropic reflection to extract, for the first time, the full orientation tensor. The orientation tensor is routinely used to synthesize fabric information and it is used in anisotropic ice flow models. We validate our approach at two Antarctic ice-core sites (EDC and EDML) in contrasting flow regimes. Spatial variability of ice-fabric characteristics in the dome-to-flank transition near Dome C is quantified with 20 more sites located along a 36 km long cross-section. Local horizontal anisotropy increases under the dome summit and decreases away from the dome summit. We suggest that this is a consequence of the non-linear rheology of ice also known as Raymond effect. On larger spatial scales, horizontal anisotropy increases with increasing distance from the dome. At most of the sites, the main driver of ice-fabric evolution is vertical compression, yet our data show that ice fabric horizontal distribution is consistent with the present horizontal flow. Our method, which uses co- and cross polarimetric radar data suitable for profiling radar applications, can constrain ice-fabric distribution on a spatial scale comparable to ice flow observations and models.

M. Reza Ershadi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2020-370', Thomas Jordan, 07 Feb 2021
  • RC2: 'Comments on tc-2020-370 by Reza Ershadi et al', Anonymous Referee #2, 26 Apr 2021

M. Reza Ershadi et al.

Data sets

Polarimetric phase-sensitive Radio Echo Sounder measurements at EDML Christmann, J., Zeising, O., and Humbert, A.

M. Reza Ershadi et al.


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Short summary
Radio-waves transmitted through the ice split up and inform us about the ice sheet interior and orientation of single ice crystals. This can be used to infer how ice flows and improve projections on how they will evolve in the future. Here we used an inverse approach and developed a new algorithm to infer ice properties from the observed radar data. We applied this technique to the radar data obtained at two EPICA drilling sites where the ice cores were used to validate our results.