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

Polycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (e) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of e, we investigated the dielectric anisotropy (Delta e) 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 Delta e 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 Delta e in the horizontal plane was 10-15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial e in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Delta e in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Delta e 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.

Automated summary

Polycrystalline ice shows macroscopic anisotropy in relative permittivity, depending on the crystal orientation fabric (COF). Using a new system, the dielectric anisotropy (Delta e) of an ice core sample was investigated. The results showed that Delta e values increased in the vertical direction with depth, and were significantly lower in the horizontal plane. The directions of the principal axes of Delta e in the horizontal plane corresponded to the preferred orientations of the c-axes.