Vertical Mixing in the Black Sea Active Layer from Small-Scale Measurement Data

A. N. Morozov*, E. V. Mankovskaya

Marine Hydrophysical Institute of RAS, Sevastopol, Russia

* e-mail: anmorozov@mhi-ras.ru

Abstract

The paper considers the methodological issues of using the G03 parameterization to estimate the vertical turbulent diffusion coefficient from current velocity and density stratification data collected with a depth increment of 4 m. Based on the expedition materials obtained during the 87th cruise of the R/V Professor Vodyanitsky (30 June to 18 July 2016) in the central sector of the northern Black Sea, this coefficient was estimated at the upper boundary of the cold intermediate layer and the depth layer of 350–390 m. The results of measurements in the acoustic Doppler current profiler exposure mode near the sea surface and at the lower sounding point were used as input data on the current velocity. In the upper sea layer at a potential density of 14.2 kg/m3, the coefficient value was 7.26×10-6 m2/s, which is close to its value of 6×10-6 m2/s in the core of the cold intermediate layer estimated from the thermal conductivity equation from the 2017 expedition measurements. The corresponding heat flux into the cold intermediate layer is 1.79 W/m2. An indirect estimate of the coefficient in the seasonal thermocline was 2.26×10-7 m2/s. This value is comparable to the molecular heat diffusion coefficient. Salt flux at a potential density value of 14.2 kg/m3 is 2,977 g/(m2·year), the corresponding salt transport through the isopycnal surface is 1.1·1015 g/year, or about 22 % of the mass of salt brought into the Black Sea by the lower Bosphorus current per year. In the layer of 350–390 m depth at a potential density value of about 16.9 kg/m3, the estimated vertical turbulent diffusion coefficient was 2.66·10-6 m2/s. The corresponding heat flux was 3.9×10-3 W/m2, or about 10 % of the geothermal flux. Salt flux of 4.110-6 g/(m2/s) corresponds to its transport of 3.9·1013 g/year through the isopycnal surface and represents 0.75 % of the mass of salt brought by the lower Bosphorus current per year. The ratio of the kinetic energy of small-scale processes to their potential energy was found to be 1.53 for the near-surface layer and 11 for the lower sounding point. This variability determines an almost threefold enhancement of vertical mixing at the upper measurement point according to the G03 parameterization.

Keywords

Black Sea, vertical mixing, shear, strain, current velocity, heat flux, salt flux

Acknowledgments

The work was performed under state assignment no. 0555-2021-0003 on topics “Operational oceanology”, no. 0555-2021-0005 “Coastal studies”.

For citation

Morozov, A.N. and Mankovskaya, E.V., 2022. Vertical Mixing in the Black Sea Active Layer from Small-Scale Measurement Data. Ecological Safety of Coastal and Shelf Zones of Sea, (4), pp. 25–38. doi:10.22449/2413-5577-2022-4-25-38

DOI

10.22449/2413-5577-2022-4-25-38

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