Structure of mesoscale eddies in the vicinity of Perth Submarine Canyon

Abstract. Mesoscale eddies represent discrete, rotating fluid particles that are different compared to their ambient aquatic environment. Understanding the dynamics of mesoscale eddies requires observations, not only of their horizontal structure, such as is available through satellite data, but also of their vertical structure. This study investigates the surface and subsurface characteristics of mesoscale eddies in the vicinity of Perth submarine canyon (30.5‒33.5º S, 112‒116º E) off the southwest coast of Western Australia. Satellite remote sensing (altimetry, temperature, and ocean color) observations were used to understand the surface characteristics while the vertical structure was investigated using ocean glider data collected between 2010 and 2017 through the Integrated Marine Observing Systems (IMOS). Eight Seaglider missions that intersected eddies revealed nine distinct vertical structures, comprising four cyclonic and five anti-cyclonic eddies. Isotherms and isohalines exhibited upwelling in cyclonic eddies, corresponding to mixed layer depth shoaling, and downwelling in anti-cyclonic eddies, aligning with mixed layer depth deepening. Anti-cyclonic eddies exhibited higher surface chlorophyll concentrations than cyclonic eddies, with coastal eddies, regardless of their sense of rotation, displaying elevated surface chlorophyll levels attributed to the entrainment of coastal waters. Offshore eddies featured lower surface chlorophyll concentrations and a distinct subsurface chlorophyll maximum.