Spatial variation of diapycnal mixing estimated from high-resolution seismic images of subsurface eddies, Bering Sea

Abstract

Turbulent mixing is a primary physical process responsible for vertical exchange of materials, heat, momentum, and energy in the ocean, and plays a key role in maintaining the overturning circulation. There are many ways to enhance ocean mixing, one of which is through oceanic eddies. However, sparse in-situ observations cannot accurately describe the structural characteristics of eddies and their contribution to turbulent mixing in the Bering Sea. In this study, we observed numerous subsurface eddies in the deep-sea region of the Bering Sea using high-resolution seismic images. These anticyclonic eddies are primarily oval-shaped or bowl-shaped, with horizontal scales of 7–65 km. The majority fall within the submesoscale range, suggesting they are mainly submesoscale eddies. They generally develop in waters shallower than 250 m, with only a few found below 300 m. Submesoscale filaments are observed on the flanks of these eddies, some of which extend downward from the eddy sides, appearing as inclined filamentous reflections. Using seismic data, we estimated diapycnal mixing and obtained its spatial distribution. The results reveal that diffusivity is significantly enhanced at the edges of eddies, especially along their sides and upper boundaries, with values reaching up to 10⁻³ m² s⁻¹. The enhanced diapycnal mixing may be related to submesoscale processes generated during eddy stirring and shear instability caused by eddy-induced velocities. Turbulent mixing induced by eddies promotes the vertical transport of heat, nutrients, and other substances in the ocean, thereby influencing primary productivity in the Bering Sea and significantly impacting the marine environment and ecosystem.