Using electron backscatter diffraction to measure full crystallographic orientation in Antarctic land-fast sea ice

• Published in: Journal of Glaciology
• Main Authors: PAT WONGPAN, DAVID J. PRIOR, PATRICIA J. LANGHORNE, KATHERINE LILLY, INGA J. SMITH
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2018
• Subjects: crystal growth; glaciological instruments and methods; ice crystal studies; sea ice–ice shelf interactions; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Antarctic; Antarc*; Ice Shelf; Ice Shelves; Journal of Glaciology; Sea ice
• Online Access: https://doi.org/10.1017/jog.2018.67; https://doaj.org/article/f21b92d62fdc42118a6a8c9190f3f6e7

We have mapped the full crystallographic orientation of sea ice using electron backscatter diffraction (EBSD). This is the first time EBSD has been used to study sea ice. Platelet ice is a feature of sea ice near ice shelves. Ice crystals accumulate as an unconsolidated sub-ice platelet layer beneath the columnar ice (CI), where they are subsumed by the advancing sea–ice interface to form incorporated platelet ice (PI). As is well known, in CI the crystal preferred orientation comprises dominantly horizontal c-axes, while PI has c-axes varying between horizontal and vertical. For the first time, this study shows the a-axes of CI and PI are not random. Misorientation analysis has been used to illuminate the possible drivers of these alignments. In CI the misorientation angle distribution from random pairs and neighbour pairs of grains are indistinguishable, indicating the distributions are a consequence of crystal preferred orientation. Geometric selection during growth will develop the a-axis alignment in CI if ice growth in water is fastest parallel to the a-axis, as has previously been hypothesised. In contrast, in PI random-pair and neighbour-pair misorientation distributions are significantly different, suggesting mechanical rotation of crystals at grain boundaries as the most likely explanation.