Abstract
The sea-ice floe size distribution (FSD) characterizes the sea-ice response to atmosphere and ocean 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 objective approach to minimize this sensitivity is presented. The FSDs are found to exhibit a single power-law regime between floe areas 50 m2 and 5 km2, 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).
Highlights
floe size distribution (FSD) are evaluated from 78 floesegmented 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
A seasonal variation in slopes is found for fixed sites in 15 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
3.1 FSD Slope Characteristics Results indicate that FSDs are characterized by a single power law with slope m for the entire regime of floe areas between 50 m2 and 5 km2 (Fig. 3a)
Summary
The Arctic Ocean is covered perennially to varying extent by sea ice floating in discrete fragments called floes, which range 20 in size from O(1) m to O(100) km (Untersteiner, 1986). A collection of high-resolution optical satellite images, spanning nearly two decades, from different locations within the Canada Basin, allows us to test and refine previous findings for a variety of settings, and for floe sizes in the range of 5 m2 to 100 km. 3, we show how FSDs exhibit a single power-law behavior spanning the full range of floe sizes and provide evidence for a shoaling of the slope of the distribution (i.e., increased ratio of larger to smaller floes) as sea-ice concentration increases. This finding is consistent with a seasonal evolution of the FSD found here, which we describe in context with previous studies in Sect. SAT is retrieved from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 Reanalysis (Hersbach et al, 2020) hourly data on single levels from 1979 to present (Hersbach et al, 2018), and taken as the mean daily value for each image region on the corresponding image day. 85
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