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

Abstract

Abstract. The crystal orientation fabric (COF) of a polar ice sheet has a significant effect on the rheology of the ice sheet. With the aim of better understanding the deformation regime of ice sheets, the work presented here investigates the COF in the upper 80 % of the Dome Fuji Station ice core in East Antarctica. Dielectric anisotropy (Δε) data were acquired as a novel indicator of the vertical clustering of COF resulting from vertical compressional strain within the dome. The Δε values were found to exhibit a general increase with depth, but with fluctuations over distances in the order of 10–102 m. In addition, significant decreases in Δε were found to be associated with depths corresponding to three major glacial to interglacial transitions. These changes in Δε are ascribed to variations in the deformational history caused by dislocation motion occurring from near-surface depths to deeper layers. Fluctuations in Δε over distances of less than 0.5 m exhibited a strong inverse correlation with Δε at depths greater than approximately 1200 m, indicating that they were enhanced during the glacial-interglacial transitions. The Δε data also exhibited a positive correlation with the concentration of chloride ions and an inverse correlation with the amount of dust particles in the ice core at greater depths corresponding to decreases in the degree of c axis clustering. Finally, we found that fluctuations in Δε persisted to approximately 80 % of the total depth of the ice sheet. These data suggest that the factors determining the deformation of ice include the concentration of chloride ions and the amount of dust particles, and that the layered contrast associated with the COF is preserved all the way from the near-surface to a depth corresponding to approximately 80 % of the thickness of the ice sheet. These findings provide important implications regarding further development of the COF under the various stress-strain configurations that the ice will experience in the deepest region, approximately 20 % of the total depth from the ice/bed interface.

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

“…Fujita et al, 2000;Saruya et al, 2022b). Here, we estimated this velocity using the relative permittivity value of ice (∼ 3.147 ± 0.010) considering depthdependent variations in crystal orientation fabrics (Azuma et al, 2000;Saruya et al, 2022a) and temperature within the ice sheet (Motoyama, 2007). Timing errors of the initial trigger in the oscilloscope are possible sources of systematic errors.…”

The Onset of Recrystallization in Polar Firn

“…Preferred crystal orientation records deformational history (Alley, 1988), and results in increased plastic anisotropy in glacier ice, affecting its flow in glaciers and ice sheets. Furthermore, fabric and texture contrasts across different climate change events are believed to cause significant variations in the rheology of ice in different ice cores (Azuma et al., 2000; Durand et al., 2007; Paterson, 1991; Saruya et al., 2022; Thorsteinnson et al., 1997). For instance, Paterson (1991) found that the strong, near‐vertical single maximum fabric in ice‐age ice, keeps the grain size small and leads to a strain rate 2.5 times faster than that in Holocene ice under the same stress and temperature.…”

A one-dimensional temperature and age modeling study for selecting the drill site of the oldest ice core around Dome Fuji, Antarctica

“…6). According to analyses of the DF ice core (Azuma et al, 1999;Saruya et al, 2022) or 3-D ice sheet modeling (Seddik et al, 2011), deformation of the ice or flow regime towards the ice bottom is complex. Thus we suggest that both horizontal and vertical ice flow should be complex as well, which may be difficult to represent by using the current formulation of vertical velocity profiles.…”