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

Abstract

Polycrystalline 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.

Development of crystal orientation fabric in the Dome Fuji ice core in East Antarctica: implications for the deformation regime in ice sheets

“…These analyses were conducted at temperatures in the range of -30 ± 1.5 °C. of a single ice crystal (0.0334) at -30 °C (see Saruya et al, 2021). Small fluctuations of De over distances from 0.02 to 0.5 m are apparent, indicating minor but significant variations in the COF within each 0.5 m long piece of ice core.…”

“…GHz (Saruya et al, 2021). The operating principle and applications of the open resonator method with regard to obtaining relative permittivity values have been previously described in the literature (Jones, 1976a,b;Cullen, 1983;Komiyama et al, 1991).…”

“…In fact, the value of a3 (2) has been shown to increase with increasing depth in ice cores drilled at dome summits due to c-axis clustering. Saruya et al (2021) reported that the relationship between De and these eigenvalues is:…”

“…To overcome these limitations, Saruya et al (2021) proposed a technique that permits the continuous non-destructive and rapid assessment of the COF in thick ice sections, based on measuring the tensorial components of the relative permittivity, e, using microwave open resonators. In this process, the difference in e between the vertical and horizontal planes is defined as the dielectric anisotropy, De.…”

High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years

“…A horizontal smoothing filter was applied to the data using a moving average over 7 s, which corresponds to a horizontal distance of about 20 m at a vehicle speed of 10 km h −1 , to increase the signal-to-noise ratio. The ice thickness at the time of observation was converted from the two-way travel time from the surface to the ice-bed interface under the assumption of a propagation velocity of 1.690×10 8 m s −1 determined based on an approximation using the relative permittivity of ice (e.g., Fujita et al, 2000;Saruya et al, 2021). Here, we estimated this velocity using the relative permittivity value of ice (∼3.147±0.010) considering depth-dependent variations of crystal orientation fabrics and temperature within the ice sheet.…”