Radar characterization of ice crystal orientation fabric and anisotropic rheology within Rutford Ice Stream, 2017-2019

We use polarimetric radar sounding to investigate variation in ice crystal orientation fabric within the near-surface (top 40-300 m) of Rutford Ice Stream, West Antarctica. To assess the influence of the fabric on ice flow, we use an analytical model to derive anisotropic enhancements of the flow law from the fabric measurements. In the shallowest ice (40-100 m) the azimuthal fabric orientation is consistent with flow-induced development and correlates with the surface strain field. Notably, toward the ice-stream margins, both the horizontal compression angle and fabric orientation tend toward 45 degrees relative to ice flow. This result is consistent with theoretical predictions of flow-induced fabric under simple shear, but to our knowledge has never been observed. The fabric orientation in deeper ice (100-300 m) is significantly misaligned with shallower ice in some locations, and therefore inconsistent with the local surface strain field. This result represents a new challenge for ice flow models which typically infer basal properties from the surface conditions assuming simplified vertical variation of ice flow. Our technique retrieves azimuthal variations in fabric but is insensitive to vertical variation, and we therefore constrain the fabric and rheology within two end-members: a vertical girdle or a horizontal pole. Our hypotheses are that fabric near the center of the ice-stream tends to a vertical girdle that enhances horizontal compression, and near the ice-stream margins tends to a horizontal pole that enhances lateral shear.

ApRES radar data were collected as part of the BEAMISH Project (NERC AFI award numbers NE/G014159/1 and NE/G013187/1). Tom Jordan would like to acknowledge support from EU Horizon 2020 grant 747336-BRISRES-H2020-MSCA-IF-2016.

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This data set had incorrect coordinates for one of the sites. In addition, some files were incorrectly labelled as belonging to one of the sites

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Date (Creation): 2020-11-03

Date (Revision): 2020-11-03

Date (Publication): 2020-11-03

Date (released): 2020-11-03

Edition: 1.0

Unique resource identifier: https://doi.org/10.5285/d5b7e5a1-b04d-48d8-a440-c010658ec146

Codespace: doi

Unique resource identifier: GB/NERC/BAS/PDC/01428

Codespace: https://data.bas.ac.uk/

Unique resource identifier: NE/G014159/1

Codespace: award

Unique resource identifier: NE/G013187/1

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Other citation details: Please cite this item as: Jordan, T., Martin, C., Brisbourne, A., Schroeder, D., & Smith, A. (2020). Radar characterization of ice crystal orientation fabric and anisotropic rheology within Rutford Ice Stream, 2017-2019 (Version 1.0) [Data set]. UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation. https://doi.org/10.5285/d5b7e5a1-b04d-48d8-a440-c010658ec146

Credit: No credit.

Status: Completed

Point of contact

Organisation name	Individual name	Electronic mail address	Role
Univeristy of Bristol	Jordan, Tom		Author
British Antarctic Survey	Martin, Carlos		Author
British Antarctic Survey	Brisbourne, Alex		Author
Stanford University	Schroeder, Dustin		Author
British Antarctic Survey	Smith, Andrew		Author
NERC EDS UK Polar Data Centre		PDCServiceDesk@bas.ac.uk	Point of contact

Maintenance and update frequency: As needed

Maintenance note: Completed

Global Change Master Directory (GCMD) Science Keywords

Theme

anisotropy
fabric
ice flow
polarimetry
radar
rheology

Place

Rutford Ice Stream Antarctica

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Spatial representation type: Text, table

Language: English

Character set: UTF8

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Geoscientific information

Begin date: 2017-01-20

End date: 2017-01-20

Supplemental Information: It is recommended that careful attention be paid to the contents of any data, and that the author be contacted with any questions regarding appropriate use. If you find any errors or omissions, please report them to polardatacentre@bas.ac.uk.

Title: European Petroleum Survey Group (EPSG) Geodetic Parameter Registry

Date (Publication): 2008-11-12

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Organisation name	Individual name	Electronic mail address	Role
European Petroleum Survey Group		EPSGadministrator@iogp.org	Publisher

Unique resource identifier: urn:ogc:def:crs:EPSG::3031

Version: 6.18.3

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NERC EDS UK Polar Data Centre		PDCServiceDesk@bas.ac.uk	Distributor

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Hierarchy level: Dataset

Statement: Methodology:

Polarimetric data acquisition follows Brisbourne et al. 2019. This paper describes the quad-polarized measurement technique that was applied in the field.

ApRES signal processing follows Brennan et al. 2014. This paper describes the processing steps applied to the raw data to generate ice-depth profiles for the phase and amplitude of radar wave.

Polarimetric data processing follows Jordan et al. 2019. This paper describes the coherence methodology that is used to determine the quality of the radar data for fabric estimation.

Data collection:

Radar: ApRES (British Antarctic Survey's Autonomous phase-sensitive Radio-Echo Sounder) - chirps of 200 to 400 MHz in time intervals of 1 s.

Data quality:

Polarimetric data quality is established from the coherence magnitude, which provides a metric for sections of the ice column where fabric can be reliably estimated. Fabric estimates could be made in the top 100-200 m of the ice column at 18 of the 20 measurement sites (maximum depth ~ 100 m near the shear-margin, and ~200 m in the ice-stream centre).

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File identifier: d5b7e5a1-b04d-48d8-a440-c010658ec146 XML

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Hierarchy level name: dataset

Date stamp: 2020-11-03

Metadata standard name: ISO 19115 Geographic Information - Metadata

Metadata standard version: ISO 19115:2003(E)

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Organisation name	Individual name	Electronic mail address	Role
NERC EDS UK Polar Data Centre		polardatacentre@bas.ac.uk	Point of contact

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