Dielectric anisotropy as indicator of crystal orientation fabric in Dome Fuji ice core: method and initial results

Shuji Fujita,Ryo Inoue,Tomotaka Saruya

doi:10.1017/jog.2021.73

Abstract

AbstractPolycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (ɛ) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of ɛ, we investigated the dielectric anisotropy (Δɛ) of a deep ice core sample obtained from Dome Fuji, East Antarctica. This technique permits the continuous nondestructive assessment of the COF in thick ice sections. Measurements of vertical prism sections along the core showed that the Δɛ values in the vertical direction increased with increasing depth, supporting previous findings of c-axis clustering around the vertical direction. Analyses of horizontal disk sections demonstrated that the magnitude of Δɛ in the horizontal plane was 10–15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial ɛ in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Δɛ in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Δɛ can be considered to represent a direct substitute for the normalized COF eigenvalues. This new method could be extremely useful as a means of investigating continuous and depth-dependent variations in COF.

Highlights

Crystal orientation fabric (COF) is one of the most important factors determining the physical properties of polar ice sheets, and both the deformation and flow of these sheets are greatly affected by the development of the COF
This work demonstrates a new methodology for the investigation of the COF in ice sheets, based on determining the tensorial components of the relative permittivity using an open resonator
Dielectric anisotropy (Δε) measurements were conducted using ice core samples recovered at Dome Fuji in East Antarctica

Summary

Introduction

Crystal orientation fabric (COF) is one of the most important factors determining the physical properties of polar ice sheets, and both the deformation and flow of these sheets are greatly affected by the development of the COF. It is generally accepted that dislocation creep is the primary process responsible for the deformation of ice-sheet ice In the dome regions of ice sheets, the vertical compressional stress resulting from the mass of the ice itself is the main source of the deformation force. Because dislocation creep results in a rotation of the c-axis toward the core axis (i.e. in the vertical direction), the Schmidt diagram for COF often indicates a single-pole maximum pattern as the depth is increased (e.g. Thorsteinsson and others, 1997; Azuma and others, 1999, 2000; Wang and others, 2003; Durand and others, 2007, 2009). Several factors related to lateral strain and shear tend to produce complex variations in the COF. Variations in the c-axis distribution along the ice core can provide a record of the deformation history caused by mechanisms such as those described above

Results

Discussion

Conclusion