The Arctic region is a rapidly changing environment, characterized by increasing rates of summer sea ice decline, rising temperatures, and lengthening open-water seasons. Arctic coastlines are considered particularly vulnerable to these changing conditions, which pose a unique threat to biological systems, human communities, and infrastructure (Forbes, 2011). Indeed the erosion rates along the Arctic coast have been accelerating (Gibbs et al., 2015, 2019; Lantuit et al., 2012), and the length of the ice-free season appears to be directly related to the higher erosion rates (Barnhart et al., 2014). While warmer temperatures are an obvious driver of erosion, in particular in areas with permafrost bluffs, mechanical processes associated with wave activity are likewise considered a leading contribution (Overeem et al., 2011). The effect of coastal sea ice in dissipating large waves and decreasing the magnitude of storm surges is reduced as the open water season lengthens and extends further into the autumn period of increased storminess in the Alaskan Arctic

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We examine the dependence of the penetration depth and fractional surface area (e.g., whitecap coverage) of bubble plumes generated by breaking surface waves on various wind and wave parameters over a wide range of sea state conditions in the North Pacific Ocean, including storms with sustained winds up to 22 ms$^{-1}$ and significant wave heights up to 10 m. Observations include arrays of freely drifting SWIFT buoys together with shipboard wind and optical video systems, which enabled concurrent high-resolution measurements of wind, waves, bubble plumes, and turbulence. We estimate bubble plume penetration depth from echograms that extend to more than 30 m depth in a surface-following reference frame collected by downward-looking echosounders integrated onboard the buoys. Our observations indicate that the mean and maximum bubble plume penetration depths exceed 10 m and 30 m beneath the surface at high winds, respectively, with a plume residence time of many wave periods. Bubble plume depths are well correlated with wind speeds, spectral wave steepness, and whitecap coverage. Plume depths scaled by total significant wave height are strongly linearly correlated with the inverse of wave age.Plume depths scaled by either wind sea or total significant wave height vary non-monotonically with increasing wind speeds. Dependencies of the combined observations on various non-dimensional predictors used for whitecap coverage estimation are also explored. This study provides first field evidence of a direct relation between bubble plume penetration depth and whitecap coverage, suggesting that the volume of bubble plumes could be estimated by remote sensing.