Subsurface eddies are an important mesoscale and submesoscale ocean phenomenon, which can be imaged with very high resolution, in particular laterally by the seismic oceanography method. Furthermore, high resolution images of physical properties such as temperature, salinity, density and sound velocity can also be derived through seismic inversion constrained by sparse CTDs/XBTs. Previous research results confirm that eddies usually show a lens-like geometry, like Meddies, or a bowl shape with no clear upper boundary. Some may also show spiral arms. These findings not only provide high resolution images of the vertical and lateral structure of eddies, but also image their associated fine structures (such as intrusions, layering, internal waves, etc.) related to mixing. The seismic oceanography method with a horizontal and vertical resolution of 10 m is appropriate for studying submesoscale currents (SMCs). In the immediate periphery of a Meddy, bands of water with numerous reflectors may be “spiral arms” of water, also called filaments. Similar patterns were found for an Arctic eddy.
Seismic images and current velocity sections identify 23 mesoscale halocline eddies on the Chukchi Borderlands, Arctic Ocean. A mesoscale anticyclonic eddy was observed, this eddy had a core with a diameter of ∼26 km, a height of 250 m, and was surrounded by submesoscale spiral bands with large slopes. There were multi-arm structures at the boundaries of the eddy, forming submesoscale spiral bands. The steep spiral arms (dip angle can be up to ∼4°) may be caused by eddy stirring. Diapycnal diffusivities estimated from seismic data were enhanced. Enhanced diffusivities at the edges of eddies may be attributed to shear instabilities at the top and bottom edges and to submesoscale motions at the lateral edges of these eddies. We highlight the enhanced mixing at the edges of eddies in the halocline can increase the upward heat flux.

subsurface eddies,Seismic Oceanography,Oceanic submesoscale processes