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On the Role of Turbulent Mixing Produced by Vertical Shear Between the Brazil Current and the Intermediate Western Boundary Current
Author(s) -
Lazaneo Cauê Z.,
Napolitano Dante C.,
Silveira Ilson C. A.,
Tandon Amit,
MacDonald Daniel G.,
Ávila Rafael A.,
Calil Paulo H. R.
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc015338
Subject(s) - turbulence , turbulence kinetic energy , dissipation , boundary layer , stratification (seeds) , mechanics , microscale chemistry , shear (geology) , turbulent diffusion , kinetic energy , atmospheric sciences , geology , physics , thermodynamics , classical mechanics , mathematics , petrology , seed dormancy , germination , botany , mathematics education , dormancy , biology
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 (O(10− 8 ) W/kg) 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.