Publications
Following publication has been announced by our department Submesoscale Dynamics. For further information please contact Dr Calil, co-author of the publication:
Lazaneo, C.Z., Napolitano, D.C., da Silveira, I.C.A., Tandon, A., MacDonald, D.G., Ávila, R.A., Calil, P.H.R. (2020): On the role of turbulent mixing produced by vertical shear between the Brazil Current and the Intermediate Western Boundary Current. Journal of Geophysical Research: Oceans, 125, e2019JC015338, doi:10.1029/2019JC015338
Abstract:
An intensification of the vertical shear is observed below the surface mixed layer at 21°S due to the mutually opposing flows of the Brazil Current and the Intermediate Western Boundary Current. The propensity to develop turbulence and mixing due to vertical shear over intense stabilizing density gradients is an important characteristic of such environments. For the first time, microscale measurements were made in the Brazil Current‐Intermediate Western Boundary Current system, providing direct quantitative values of the turbulent fluctuations. Peaks of relative strong dissipation rates of turbulent kinetic energy were observed close to the base of the surface mixed layer. On the other hand, prominent peaks of turbulent kinetic energy dissipation rates of up to 2 orders of magnitude higher than the background were observed at deeper levels, where stratification begins to lose intensity. Analyzing such peaks, caused by intense vertical shear or weak stratification—and sometimes both—, allows a characterization of the local mixing processes and the role played by vertical exchanges of biogeochemical properties. Based on the estimated nitrate gradient and the vertical diffusivity, we show that turbulent mixing driven by vertical shear plays an important role in the supply of nitrate to the upper layer.
Plain Language Summary:
Turbulent mixing across the density surfaces can bring nutrient‐rich waters from the subsurface to the upper sunlit layer of the ocean, therefore, modulating the primary productivity in an oligotrophic ocean. Based on measurements of small‐scale shear variance, we found that the interaction between the poleward‐flowing Brazil Current and the Intermediate Western Boundary Current flowing underneath in the opposite direction enhances the upper‐ocean mixing through shear instabilities. The destabilizing influence of the velocity shear overcomes the stabilizing effect of the stratification. The mixing on the interface between these two western boundary currents may provide an important route for local nutrient exchanges.
