Characterizing the sea-ice floe size distribution in the Canada Basin from high-resolution optical satellite imagery

The sea-ice floe size distribution (FSD) characterizes the sea-ice response to atmospheric and oceanic forcing and is important for understanding and modeling the evolving ice pack in a warming Arctic. FSDs are evaluated from 78 floe-segmented high-resolution (1 m) optical satellite images capturing a range of settings and sea-ice states during spring through fall from 1999 to 2014 in the Canada Basin. For any given image, the structure of the FSD is found to be sensitive to a classification threshold value (i.e., to specify an image pixel as being either water or ice) used in image segmentation, and an approach to account for this sensitivity is presented. The FSDs are found to exhibit a single power-law regime between floe areas 50 m(2) and 5 km(2), characterized by exponents (slopes in log-log space) in the range -2.03 to -1.65. A distinct linear relationship between slopes and sea-ice concentrations is found, with steeper slopes (i.e., a larger proportion of smaller to larger floes) corresponding to lower sea-ice concentrations. Further, a seasonal variation in slopes is found for fixed sites in the Canada Basin that undergo a seasonal cycle in sea-ice concentration, while sites with extensive sea-ice cover year-round do not exhibit any seasonal change in FSD properties. Our results suggest that sea-ice concentration should be considered in any characterization of a time-varying FSD (for use in sea-ice models, for example).

Automated summary

The structure of sea-ice floe size distribution (FSD) is sensitive to classification threshold values, showing a power-law regime between certain floe areas with slopes correlating to sea-ice concentrations. There is a seasonal variation in slopes for sites with seasonal sea-ice concentration cycles, while sites with year-round sea-ice cover show no seasonal changes in FSD properties.