Metrics for interpreting the microstructure of sea ice using X-ray micro-computed tomography

- We present a detailed methodology for studying sea ice using μCT and develop new metrics for analyzing brine morphology.
- We determine the representative elementary volume for CT analysis of sea ice is a cubic sub-sample measuring 6.0 mm on edge.
- For field-collected ice, we observed, vertical cylindrical channels that had morphology varying with depth and ice type.
- We found air pockets to be vertically elongated in multi-year ice while being more spherical in first-year ice.

As the character and dynamics of sea ice change in a rapidly changing climate, it is critical to have a detailed understanding of the fine microstructure of sea ice. Advances in X-ray micro-computed tomography (μCT) technology have enabled non-destructive three dimensional analysis of the brine channel morphology with resolution down to several microns. In this study, we examine six ice cores collected from the Ross Sea, Antarctica. Metrics were developed to describe the shape, size, and topology of the brine channels and air pockets in sea ice. A cubic sub-sample measuring 6.0 mm on edge was found to be the representative elementary volume for sea ice μCT analysis with these metrics. All samples were observed to have vertically oriented cylindrical brine channels, with increased branching and connectivity observed at lower depths. The highest degree of vertical anisotropy was detected through the middle, with increased variability near the top and bottom of each core. Air pockets were found to be mostly spherical in shape, except vertically elongated in multi-year ice.