Microstructural evolution in the fine-grained region of the Siple Dome (Antarctica) ice core

Abstract

An in-depth analysis of seven samples from the Siple Dome (Antarctica) ice core, using optical microscopy and electron backscatter diffraction, illustrates rotational recrystallization or polygonization in the fine-grained region of the core between 700 and 800 m. Between 640 and 700 m, the microstructure is characterized by a bimodal grain-size distribution and a broken girdle fabric with evidence of polygonization. From 727 to 770 m, mean grain size decreases and a single-maximum fabric is found, and, by 790m, mean grain size has again increased and a multiple-maxima fabric manifests itself. We compare grain-size distribution, c-and a-axis orientation, and misorientation between adjacent grains. We found that misorientations between adjacent grains in the 727-770m region were predominantly low-angle and typically around a common a-axis, suggesting polygonization. This conclusion is supported by radar evidence of a physical disturbance at 757 m, which may be correlated with higher than usual strain in the 700-800m range. Below 770m, larger less regular misorientations and textural evidence show that migration recrystallization is the primary recrystallization mechanism.