Thin-section photographs and associated c-axis fabrics of the Siple Dome core are presented in Figure 6. All fabric diagrams except two are based on equal-area (Schmidt-net) projections of c axes measured in horizontal thin sections. The exceptions are two diagrams from 916 and 948 m, where paired vertical sections were used and the c-axis measurements subsequently rotated into the horizontal plane. The center of each fabric diagram coincides in all cases with the vertical axis of the core. As clearly demonstrated in Figure 6, changes in the texture of the ice at Siple Dome were accompanied by significant changes in aggregate c-axis orientation. At 60m depth, ice from directly below the firnice transition at Siple Dome featured a random fabric, which was still in evidence at 80 m. However, by 99m, signs of a broad vertical clustering of c axes begin to appear and this trend is maintained and somewhat strengthened to at least 261m depth. Such broad clustering of the c axes, coupled with significant changes in the shapes and sizes of crystals that are clearly discernible in the thin-section photographs in Figure 6, is consistent with a deformational process dominated by rotation of the c axes towards the axis of vertical compression. As suggested earlier, the diminished grain size observed at 261m together with significantly increased clustering of the c axes and widespread undulose extinction of the crystals might indicate the onset of enhanced deformation associated with rotation and bending of basal glide planes of crystals under uniaxial vertical compression.

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1：Optical properties of ice and snow. Philosophical Transactions of the Royal Society A, 2019, 377(2146): 20180161.

2：Physical properties, crystalline textures and c-axis fabrics of the Siple Dome (Antarctica) ice core. Journal of Glaciology, 2007, 53(183): 573-584.