23 / 2023-07-24 15:07:49

Energetic Submesoscale Stirring in the Stratified Layer of a Cyclonic Eddy

Submesoscale stirring, cyclonic eddy, vertical transport, isopycnal mixing

Submesoscale dynamics are ubiquitous in the upper ocean and play a crucial role in vertical transport of tracers. Here, we use targeted high-resolution observations conducted during summer in the South China Sea to investigate the submesoscale stirring in the subsurface of a cyclonic eddy. Our results reveal energetic submesoscale stirring or mixing along isopycnals, resulting in along-isopycnal transport of tracers. The stirring along slantwise isopycnals disrupted the mesoscale coherence and drove significant vertical exchange of tracers, which was dynamically ascribed to ageostrophic instabilities. Compared to diapycnal mixing, the submesoscale isopycnal stirring serves as the primary driver of vertical flux, crucially resupplying the elevated phytoplankton biomass in the core of the coherent cyclonic eddy with nutrients. These findings provide a dynamical explanation for the formation and maintenance of local subsurface chlorophyll maxima within cyclonic eddies, highlighting the important role of submesoscale dynamics in structuring marine ecosystems.