Landfast sea ice break out patterns in the northern Bering Sea observed from C-band Synthetic Aperture Radar

Arctic sea ice is declining in areal extent and seasonal duration, affecting stable landfast sea ice regimes. These landfast ice regimes are vital platforms for local indigenous subsistence hunters and epontic primary production species supporting local and regional food webs. Under changing thermodynamic and mechanical stresses, landfast ice can become more prone to break out events - unexpected mid-season detachments from the coastline. However, the prevalence of break out events in the landfast ice annual cycle on an interannual and decadal basis is generally understudied. Here, we detect and quantify landfast ice break-out events at St. Lawrence Island in the Northern Bering Sea. We accomplished this using C-band Synthetic Aperture Radar (SAR) imagery to detect landfast ice cover. We also advanced a geospatial analysis method to identify break-out events and distinguish such occurrences from end-of-season breakups. Results reveal that 35 break-outs occurred across four sections of the St. Lawrence Island coastline from 1996 - 2019, with 74 % of break-outs occurring on the northern coastlines. Break-outs generally occurred during annual cycles with higher than average landfast ice cover. During the break-out events, maximum temperatures seldom exceed conditions promoting melt, whereas wind speeds are, on average, 2 m/s faster compared to end-of-season breakup events. However, additional datasets are needed to understand better the influence of tidal amplitude and ocean currents on detected break-out occurrence and location. Our study provides the basis for future research to understand break-out events in landfast ice annual cycles at fine spatial scales unavailable in existing sea ice datasets.

Automated summary

Arctic sea ice decline affects stable landfast ice regimes, which are vital for indigenous hunters and local food webs. Break-out events in landfast ice cycles are generally understudied. Using SAR imagery, we detected and quantified break-out events on St. Lawrence Island. Results show 35 break-outs occurred from 1996-2019, mostly on the northern coastlines, with higher landfast ice cover and faster wind speeds compared to end-of-season breakups. Further research is needed to understand the influence of tidal amplitude and ocean currents on break-out occurrence.