Expansion of the Wave Action Season Across Alaska's Marginal Seas

Abstract Rapid loss of Arctic sea ice is transforming wave dynamics across Alaska's marginal seas, expanding the period when surface waves actively develop and propagate. This study quantifies how the wave action season (WAS) has evolved in the past 45 years across northern and western Alaska using a multi‐decadal hindcast validated against satellite altimetry from the ESA Climate Change Initiative and ICESat‐2 ATL12 data sets. Utilizing the coupled ADCIRC‐SWAN model, it accurately reproduces the spatial distribution and magnitude of observed wave heights, providing a basis for assessing temporal and spatial trends in the WAS characteristics. Results show a consistent regional expansion of the WAS throughout Alaska. The onset of wave activity has advanced by approximately 0.8–2.0 days·yr −1 across the Chukchi and Beaufort Seas, with localized maxima near Wainwright exceeding 2 days·yr −1 . The end of the season has been delayed by up to 1.4 days·yr −1 , yielding a net lengthening of 1–2 days·yr −1 across most of the state's nearshore areas. These changes result in total lengthening exceeding 100 days in parts of the Beaufort and Chukchi Seas over the past 45 years. Duration trends form a continuous corridor of positive change along the Chukchi and Beaufort Seas and gradually weaken southward into the northern Bering Sea. These results demonstrate that the WAS has expanded consistently across Alaska's marginal seas over the last four decades, reflecting a sustained shift toward longer periods of active wave development as sea‐ice retreat extends fetch.