from 01.01.1988 until now
Sevastopol, Sevastopol, Russian Federation
Purpose. The purpose of the study is to assess the vertical turbulent diffusion coefficient in the lower part of main pycnocline in the areas of continental slope and deep part of the Black Sea. Methods and Results. The data collected during the 87th cruise of R/V “Professor Vodyanitsky” which was conducted in the central sector of the northern Black Sea from June 30 to July 18 in 2016, are used. The profiles of temperature, salinity and current velocity were measured by CTD/LADCP probes. A method for applying the G03 parameterization to the ~ 200 m thickness layer located between the iso-pycns with conditional density 15.5 and 16.8 kg/m3 is proposed. To suppress measurement noise, the isopycnal averaging over the station ensemble as well as the approximation of the resulting parameter profiles by power functions are applied. The difference between the transfer functions of CTD and LADCP data processing is taken into account when integrating the canonical spectrum of internal waves. The data from 20 deep-sea stations permitted to obtain the buoyancy frequency profile averaged over the isopycns, which demonstrated the layers of its power and exponential dependences on depth. The methodological problems in applying the G03 parameterization to the lower part of the Black Sea main pycnocline are discussed in detail including the graphic presentation of data. The profiles of verti-cal turbulent diffusion coefficient show its almost constant value of ~ 210-6 m2/s in the region of continental slope and its linear increase with depth from 110-6 m2/s to 210-6 m2/s in the deep part of the sea. The maximum value of calculated heat fluxes reaches 12 mW/m2 and confirms their insignificant effect on the heating of cold intermediate layer. The salt flux at the layer upper boundary in the area of continental slope is 610-5 g/(m2s) and in the deep part of the sea – ~ 310-5 g/(m2s). At the layer lower boundary, the salt fluxes are almost the same for both areas and constitute ~ 510-6 g/(m2s). As for the shear-to-strain ratio, its sharp increase with depth is evident, and a significant difference in the nature of small-scale processes at the boundaries of lower part of the main pycnocline is clearly pronounced. Conclusions. The estimate of vertical turbulent diffusion coefficient obtained using the G03 parameteri-zation is in good agreement with the values resulted from the microstructural sounding in other sea re-gions. However, the issue of comparability of the estimates remains open and requires synchronous measurements with microstructural and CTD/LADCP probes.
Black Sea, main pycnocline, vertical turbulent mixing, Rim Current, current velocity shear, strain
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