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Abstract:
The Bering Sea in winter (October-April) is defined by a seasonal ice cover and stormy seas; average significant wave height (SWH) is 2.7 m, double the May-September average. Every winter, 20 days on average exhibit SWHs larger than 9 m. Our analysis of surface wind and wave conditions suggests enhanced storminess. The past 5 years are among the 6 stormiest in the last 20 years, indicated by an increase of 0.5 m/s/decade in the highest 1% of surface wind speeds and an increase of 0.5 m/decade in the highest 1% of SWHs. Observations also show a trend in Bering Sea ice extent of -30.5 %/decade in March between 2012-2022. This is in stark contrast to the previous three decades when ice extent was relatively stable (+1.7 %/decade). If we were to assume a continuing linear decline in ice extent, current conditions suggest the Central Shelf area (St. Matthew Island) would be ice free in winter by the early 2030s. Since the sea ice and storm seasons overlap, we hypothesize that a decline in sea ice would increase the frequency of high waves over the shelf, severely impacting coastal communities. In September 2022, extratropical cyclone Merbok caused unprecedented wave conditions (SWH > 15 m) over the shelf that were uncharacteristic for the season, resulting in widespread coastal inundation and property damage. This demonstrated the emerging threat storms pose in a future where sea ice is largely absent from the Bering Sea shelf region in winter, when severe storms are common.
