The microstructure of meteoric ice from Vostok, Antarctica

• Published in: Journal of Glaciology
• Main Authors: Obbard, Rachel, Baker, Ian
• Format: Text
• Language: unknown
• Published: Dartmouth Digital Commons 2006
• Subjects: Glaciology; Vostok Station; Antarc*; Antarctica
• Online Access: https://digitalcommons.dartmouth.edu/facoa/63; https://doi.org/10.3189/172756507781833901; https://digitalcommons.dartmouth.edu/context/facoa/article/1062/viewcontent/65.pdf

The 3623 m long, 5G core collected at Vostok station, Antarctica, contains alternating layers of meteoric ice with two distinctly different microstructures. In this paper, we present the microstructure and impurity content of a number of specimens ranging in depth from 97 to 3416 m, describe in detail the characteristics of the different layers and propose a mechanism for their microstructural development. Digital image analysis, ion chromatography, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to measure texture and the location and type of impurities; electron backscatter diffraction was used to determine crystal orientation. The ice associated with interglacial periods is characterized by relatively coarse grains and a strong preferred orientation of the c axes in a plane encompassing the coring direction, producing a vertical-girdle fabric. In contrast, ice from glacial periods is characterized by a much smaller grain size and a strong single-maximum fabric, where the c axes are clustered around the vertical. Calcium is uniquely present in the grain boundaries of the fine-grained glacial layers, and its effect on grain-boundary mobility and the misorientation dependence of mobility can explain the development of the discontinuous microstructure seen in glacial ice at Vostok station.