Cross‐Slope Buoyancy Fluxes Cause Intense Asymmetric Generation of Submesoscale Eddies on the Periphery of the Black Sea Mesoscale Anticyclones

Abstract

AbstractSubmesoscale dynamics significantly affect the turbulence regime and is characterized by pronounced time variability, the reasons of which are still poorly known. In our study, we use high‐resolution (1 km) numerical model NEMO and satellite data in the Black Sea to demonstrate that one of the main processes impacting on the intensity of submesoscale dynamics in the marginal seas is the cross‐slope advection by mesoscale anticyclones. Such large eddies entrain the brackish shelf waters into their orbital motion and cause the strong rise of vertical and horizontal gradients of buoyancy. The emergence of baroclinic instability causes the generation of periodic submesoscale structures, among which cyclonic eddies have the largest vorticity. Our analysis shows that the presented mechanism is one of the main reasons for the intraannual variability of submesoscale dynamics over the continental slope of the Black Sea. This process also causes a strong asymmetry in the vertical structure of the mesoscale anticyclones. The generation of the submesoscale eddies and related vertical and horizontal exchange are significantly more intense on that side of the anticyclone, where current is directed offshore. Intensification of submesoscale motions in the zone of the brackish water entrainment is one of the probable reasons for the rapid and effective mixing of the shelf and open sea waters, often observed in satellite data.