Vertical Mixing in the Lower Part of Main Pycnocline in the Black Sea

A. N. Morozov

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

e-mail: anmorozov@mhi-ras.ru

Abstract

Purpose. This study aims to evaluate the vertical turbulent diffusion coefficient in the lower part of the main pycnocline in the areas of continental slope and deep waters of the Black Sea.

Methods and Results. Data were collected during the 87th cruise of R/V Professor Vodyanitsky in the central sector of the northern Black Sea from June 30 to July 18, 2016. Profiles of temperature, salinity, and current velocity were obtained using CTD/LADCP probes. A method applying the G03 parameterization to a layer ~ 200 m thick, spanning isopycnals with conditional densities between 15.5 and 16.8 kg/m3, is proposed. To suppress measurement noise, isopycnal averaging across the station ensemble and approximation of the resulting parameter profiles using power functions were employed. Differences in the transfer functions for CTD and LADCP data processing were accounted for when integrating the canonical spectrum of internal waves. Data from 20 deep-sea stations enabled the derivation of buoyancy frequency profile averaged over the isopycnals, revealing layers of its power and exponential dependences on depth. The methodological challenges of applying the G03 parameterization to the lower part of the Black Sea’s main pycnocline are discussed in detail, including graphical data presentation. The profiles of the vertical turbulent diffusion coefficient K</em>G03 indicate a nearly constant value of ~ 2·10-6 m2/s in the continental slope region, while in the deep waters of the sea, it increases linearly with depth from 1·10-6 m2/s to 2·10-6 m2/s. The maximum calculated heat flux reaches 12 mW/m2, confirming its negligible impact on the heating of the cold intermediate layer. The salt flux at the upper boundary of the layer is 6·10-5 g/(m2·s) in the continental slope region and ~ 3·10-5 g/(m2·s) in the deep waters. At the lower boundary of the layer, salt fluxes are nearly identical in both regions, approximately ~ 5·10-6 g/(m2·s). The shear-to-strain ratio exhibits a pronounced increase with depth, highlighting significant differences in the characteristics of small-scale processes at the boundaries of the lower part of the main pycnocline.

Conclusions. The vertical turbulent diffusion coefficient estimated using the G03 parameterization agrees well with the values obtained from the microstructural sounding in other marine regions. However, the comparability of these estimates remains unresolved and requires synchronous measurements using microstructural and CTD/LADCP probes.

Keywords

Black Sea, main pycnocline, vertical turbulent mixing, Rim Current, current velocity shear, strain

Acknowledgements

The study was conducted within the framework of the state assignment theme of FSBSI FRC MHI FNNN-2024-0012 “Operational Oceanology”.

Original russian text

Original Russian Text © A. N. Morozov, 2025, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 41, Iss. 5, pp. 586–598 (2025)

For citation

Morozov, A.N., 2025. Vertical Mixing in the Lower Part of Main Pycnocline in the Black Sea. Physical Oceanography, 32(5), pp. 601-612.

References

  1. Zatsepin, A.G., Golenko, N.N., Korzh, A.O., Kremenetskii, V.V., Paka, V.T., Poyarkov, S.G. and Stunzhas, P.A., 2007. Influence of the Dynamics of Currents on the Hydrophysical Structure of the Waters and the Vertical Exchange in the Active Layer of the Black Sea. Oceanology, 47(3), pp. 301-312. https://doi.org/10.1134/S0001437007030022
  2. Munk, W.H., 1966. Abyssal Recipes. Deep Sea Research and Oceanographic Abstracts, 13(4), pp. 707-730. https://doi.org/10.1016/0011-7471(66)90602-4
  3. Munk, W.H. and Anderson, E.R., 1948. Notes on the Theory of the Thermocline. Journal of Marine Research, 7(3), pp. 276-295.
  4. Polzin, K.L., Naveira Garabato, A.C., Huussen, T.N., Sloyan, B.M. and Waterman, S., 2014. Finescale Parameterizations of Turbulent Dissipation. Journal of Geophysical Research: Oceans, 119(2), pp. 1383-1419. https://doi.org/10.1002/2013JC008979
  5. Le Boyer, A., Couto, N., Alford, M.H., Drake, H.F., Bluteau, C.E., Hughes, K.G., Naveira Garabato, A.C., Moulin, A.J., Peacock, T. [et al.], 2023. Turbulent Diapycnal Fluxes as a Pilot Essential Ocean Variable. Frontier in Marine Science, 10, 1241023. https://doi.org/10.3389/fmars.2023.1241023
  6. Sasaki, Y., Yasuda, I., Katsumata, K., Kouketsu, S. and Uchida, H., 2024. Turbulence across the Antarctic Circumpolar Current in the Indian Southern Ocean: Micro-Temperature Measurements and Finescale Parameterizations. Journal of Geophysical Research: Oceans, 129(2), e2023JC019847. https://doi.org/10.1029/2023JC019847
  7. Takahashi, A. and Hibiya, T., 2018. Assessment of Finescale Parameterizations of Deep Ocean Mixing in the Presence of Geostrophic Current Shear: Results of Microstructure Measurements in the Antarctic Circumpolar Current Region. Journal of Geophysical Research: Oceans, 124(1), pp. 135-153. https://doi.org/10.1029/2018JC014030
  8. Gregg, M.C. and Yakushev, E., 2005. Surface Ventilation of the Black Sea’s Cold Intermediate Layer in the Middle of the Western Gyre. Geophysical Research Letters, 32(3), 2004GL021580. https://doi.org/10.1029/2004GL021580
  9. Samodurov, A.S., Chukharev, A.M., Kazakov, D.A., Pavlov, M.I. and Korzhuev, V.A., 2023. Vertical Turbulent Exchange in the Black Sea: Experimental Studies and Modeling. Physical Oceanography, 30(6), pp. 689-713.
  10. Zatsepin, A.G., Ostrovskii, A.G., Kremenetskiy, V.V., Nizov, S.S., Piotukh, V.B., Soloviev, V.A., Shvoev, D.A., Tsibul’sky, A.I., Kuklev, S.B. [et al.], 2014. Subsatellite Polygon for Studying Hydrophysical Processes in the Black Sea Shelf-Slope Zone. Izvestiya, Atmospheric and Oceanic Physics, 50(1), pp. 13-25. https://doi.org/10.1134/S0001433813060157
  11. Podymov, O.I., Zatsepin, A.G. and Ostrovsky, A.G., 2017. Vertical Turbulent Exchange in the Black Sea Pycnocline and Its Relation to Water Dynamics. Oceanology, 57(4), pp. 492-504. https://doi.org/10.1134/S0001437017040142
  12. Podymov, O.I., Zatsepin, A.G. and Ostrovskii, A.G., 2023. Fine Structure of Vertical Density Distribution in the Black Sea and Its Relationship with Vertical Turbulent Exchange. Journal of Marine Science and Engineering, 11(1), 170. https://doi.org/10.3390/jmse11010170
  13. Morozov, A.N. and Lemeshko, E.M., 2006. Methodical Aspects of the Application of Acoustic Doppler Current Profilers in the Black Sea. Physical Oceanography, 16(4), pp. 216-233. https://doi.org/10.1007/s11110-006-0027-8
  14. Gregg, M.C., Sanford, T.B. and Winkel, D.P., 2003. Reduced Mixing from the Breaking of Internal Waves in Equatorial Waters. Nature, 422, pp. 513-515. https://doi.org/10.1038/nature01507
  15. Ferron, B., Kokoszka, F., Mercier, H. and Lherminier, P., 2014. Dissipation Rate Estimates from Microstructure and Finescale Internal Wave Observations along the A25 Greenland–Portugal OVIDE Line. Journal of Atmospheric and Oceanic Technology, 31(11), pp. 2530-2543. https://doi.org/10.1175/JTECH-D-14-00036.1
  16. Fine, E.C., Alford, M.H., MacKinnon, J.A. and Mickett, J.B., 2021. Microstructure Mixing Observations and Finescale Parameterizations in the Beaufort Sea. Journal of Physical Oceanography, 51(1), pp. 19-35. https://doi.org/10.1175/JPO-D-19-0233.1
  17. Baumann, T.M., Fer, I., Schulz, K. and Mohrholz, V., 2023. Validating Finescale Parameterizations for the Eastern Arctic Ocean Internal Wave Field. Journal of Geophysical Research: Oceans, 128(11), e2022JC018668. https://doi.org/10.1029/2022JC018668
  18. Henyey, F.S., Wright, J. and Flatté, S.M., 1986. Energy and Action Flow through the Internal Wave Field: An Eikonal Approach. Journal of Geophysical Research: Oceans, 91(C7), pp. 8487-8495. https://doi.org/10.1029/JC091iC07p08487
  19. Polzin, K.L., Toole, J.M. and Smith, R.W., 1995. Finescale Parameterizations of Turbulent Dissipation. Journal of Physical Oceanography, 25(3), pp. 306-328. https://doi.org/10.1175/1520-0485(1995)025%3C0306:FPOTD%3E2.0.CO;2
  20. Morozov, A.N. and Mankovskaya, E.V., 2022. Characteristics of the Bottom Convective Layer of the Black Sea Based on in-situ Data (July, 2016). Physical Oceanography, 29(5), pp. 524-535. https://doi.org/10.22449/1573-160X-2022-5-524-535
  21. Ivanov, V.A. and Belokopytov, V.N., 2013. Oceanography of the Black Sea. Sevastopol: ECOSY-Gidrofizika, 210 p.
  22. Morozov, A.N. and Mankovskaya, E.V., 2021. Spatial Characteristics of the Black Sea Cold Intermediate Layer in Summer, 2017. Physical Oceanography, 28(4), pp. 404-413. https://doi.org/10.22449/1573-160X-2021-4-404-413
  23. Stanev, E.V., Chtirkova, B. and Peneva, E., 2021. Geothermal Convection and Double Diffusion Based on Profiling Floats in the Black Sea. Geophysical Research Letters, 48(2), e2020GL091788. https://doi.org/10.1029/2020GL091788
  24. Samodurov, A.S., 2016. Complimentarity of Different Approaches for Assessing Vertical Turbulent Exchange Intensity in Natural Stratified Basins. Physical Oceanography, (6), pp. 32-42. https://doi.org/10.22449/1573-160X-2016-6-32-42
  25. Garrett, C. and Munk, W., 1975. Space-Time Scales of Internal Waves: A Progress Report. Journal of Geophysical Research, 80(3), pp. 291-297. https://doi.org/10.1029/JC080i003p00291
  26. Cairns, J.L. and Williams, G.O., 1976. Internal Wave Observations from a Midwater Float, 2. Journal of Geophysical Research, 81(12), pp. 1943-1950. https://doi.org/10.1029/JC081i012p01943
  27. Morozov, A.N., 2025. Vertical Mixing in the Main Pycnocline of the Black Sea in Summer. Physical Oceanography, 32(3), pp. 271-282.
  28. Kunze, E., Firing, E., Hummon, J.M., Chereskin, T.K. and Thurnherr, A.M., 2006. Global Abyssal Mixing Inferred from Lowered ADCP Shear and CTD Strain Profiles. Journal of Physical Oceanography, 36(8), pp. 1553-1576. https://doi.org/10.1175/JPO2926.1
  29. Gregg, M.C., 1989. Scaling Turbulent Dissipation in the Thermocline. Journal of Geophysical Research: Oceans, 94(C7), pp. 9686-9698. https://doi.org/10.1029/JC094iC07p09686
  30. Fer, I., 2006. Scaling Turbulent Dissipation in an Arctic Fjord. Deep Sea Research Part II: Topical Studies in Oceanography, 53(1-2), pp. 77-95. https://doi.org/10.1016/j.dsr2.2006.01.003
  31. Chinn, B.S., Girton, J.B. and Alford, M.H., 2016. The Impact of Observed Variations in the Shear-to-Strain Ratio of Internal Waves on Inferred Turbulent Diffusivities. Journal of Physical Oceanography, 46(11), pp. 3299-3320. https://doi.org/10.1175/JPO-D-15-0161.1
  32. Zhurbas, V.M., Zatsepin, A.G., Grigor’eva, Yu.V., Poyarkov, S.G., Eremeev, V.N., Kremenetsky, V.V., Motyzhev, S.V., Stanichny, S.V., Soloviev, D.M. [et al.], 2004. Water Circulation and Characteristics of Currents of Different Scales in the Upper Layer of the Black Sea from Drifter Data. Oceanology, 44(1), pp. 30-43.
  33. Khimchenko, E., Ostrovskii, A., Klyuvitkin, A. and Piterbarg, L., 2022. Seasonal Variability of Near-Inertial Internal Waves in the Deep Central Part of the Black Sea. Journal of Marine Science and Engineering, 10(5), 557. https://doi.org/10.3390/jmse10050557
  34. Khimchenko, E. and Ostrovskii, A., 2024. Observations of Near-Inertial Internal Waves over the Continental Slope in the Northeastern Black Sea. Journal of Marine Science and Engineering, 12(3), 507. https://doi.org/10.3390/jmse12030507
  35. Morozov, A.N., Mankovskaya, E.V. and Fedorov, S.V., 2021. Inertial Oscillations in the Northern Part of the Black Sea Based on the Field Observations. Fundamental and Applied Hydrophysics, 14(1), pp. 43-53. https://doi.org/10.7868/S2073667321010044 (in Russian).

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