Thermohaline Structure and Salt Fingering in the Lomonosov Equatorial Undercurrent as Observed in April 2017

  • Tatiana A. Demidova
Part of the Springer Oceanography book series (SPRINGEROCEAN)


We analyze CTD casts accompanying ADCP velocity measurements along 33° W in the Atlantic in the region of the Lomonosov Equatorial Undercurrent (EUC) on April 14, 2017. Three CTD stations were located at the equator and 30 miles south and north of it in the core of the undercurrent. We focus on the study of the thermohaline stratification in the subsurface layer with intense development of the stepwise structures on the temperature, salinity, and density profiles at the depths below the salinity and velocity cores. The estimates of the water stratification types are based on the analysis of the profiles of temperature, salinity, and density together with the computed stability parameters such as the density ratio and vertical thermohaline stability. The high-gradient parts of steps (“sheets”) up to 15 m thick against the background of sharp negative T and S gradients were related to the small intervals of peaks of positive stable stratification E > 0 and low values of density ratio 1 < R < 2. Such intervals are statically unstable and meet the strict criteria of conditions favorable for double diffusion convection in the form of salt fingers. This provides evidence of the high probability of vertical mixing of this type. It implies that in the course of propagation of the high-salinity EUC, a convective salt fingering mechanism may provide vertical redistribution of salt and heat from the core of the EUC to the deeper layers. Variations in the intensity of the processes with latitude and indications of large horizontal scales of fingering processes are found.



The field works were supported by the Program of the Presidium of the Russian Academy of Sciences (project I3Π). Data analysis was supported by the Russian Science Foundation (project no. 14-50-00095).


  1. 1.
    Bourlès, B., et al. (2008). The PIRATA program: History, accomplishments, and future directions. Bulletin of the American Meteorological Society, 89, 1111–1125.CrossRefGoogle Scholar
  2. 2.
    Bubnov, V. A., Moroshkin, K. V., Egorikhin, V. D., & Matveeva, Z. N. (1976). Variability of currents in the equatorial Atlantic. Okeanologiya, 16, 408–414.Google Scholar
  3. 3.
    Carlin, L. N., Klyuykov, E. Y., Kutko, V. P. (1988). Small-scale structure of hydrophysical fields of the upper layer of the ocean (p. 162) Moscow: Gidrometeoizdat. (in Russian).Google Scholar
  4. 4.
    Claret, M., Rodríguez, R., & Pelegrí, J. L. (2012). Salinity intrusion and convective mixing in the Atlantic equatorial undercurrent. Scientia Marina, 76(S1), 117–129. Scholar
  5. 5.
    Demidova, T. A. (2017). Distribution of thermohaline parameters of the Lomonosov undercurrent as an evidence of its static instability. In The modern methods and means of oceanological research (MSOI-2017) Conference materials, Moscow (pp. 148–149). (in Russian).Google Scholar
  6. 6.
    Demidova, T. A., Frey, D. I. (2017). On the velocity field of the Lomonosov current as observed on the ship route. In The modern methods and means of oceanological research (MSOI-2017) Conference materials, Moscow (pp. 150–151). (in Russian).Google Scholar
  7. 7.
    Fedorov, K. N. (1976). Fine thermohaline structure of ocean water (p. 184). Leningrad:Gidrometeoizdat. (in Russian).Google Scholar
  8. 8.
    Fedorov, K. N. (1984). Conditions of stratification and convection in the form of salt fingers in the ocean. Doklady AN SSSR (Earth Science Sections), 275(3), 749–753.Google Scholar
  9. 9.
    Fedorov, K. N., & Pereskokov, A. I. (1986). Typification of thermohaline conditions of stratification in the World Ocean. Meteorology and Hydrology, 12, 71–77. (in Russian).Google Scholar
  10. 10.
    Gershuni, G. Z., & Zhukhovitsky, E. M. (1963). About a convective instability of two-component mixture in the gravitational field. Applied Mathematics and Mechanics, 27(2), 301–308. (in Russian).Google Scholar
  11. 11.
    Gershuni, G. Z., & Zhukhovitsky, E. M. (1972). Convective stability of incompressible liquid (p. 392). Moscow, Nauka. (in Russian).Google Scholar
  12. 12.
    Gregg, M. C. (1976). Temperature and salinity microstructure of the Pacific Equatorial Undercurrent. Journal of Geophysical Research, 81, 1180–1196.Google Scholar
  13. 13.
    Gregg, M. C., Peters, H., Wesson, J. C., Oakey, N. S., & Shay, T. J. (1985). Intensive measurements of turbulence and shear in the equatorial undercurrent. Nature, 318, 140–144.CrossRefGoogle Scholar
  14. 14.
    Jones, J. H. (1973). Vertical mixing in equatorial undercurrent. Journal of Physical Oceanography, 3, 286–296.CrossRefGoogle Scholar
  15. 15.
    Katz, E. J., Bruce, J. G., & Petrie, B. D. (1979). Salt and mass flux in the Atlantic equatorial undercurrent. Deep-Sea Research GATE Supplement II to V, 26, 137–160.Google Scholar
  16. 16.
    Knauss, J. A. (1960). Measurements of the Cromwell Current. Deep Sea Research, 6, 265–286.CrossRefGoogle Scholar
  17. 17.
    Knauss, J. A. (1960). Further measurements and observations on the Cromwell Current. Journal of Marine Research, 24, 204–240.Google Scholar
  18. 18.
    Kolesnikov, A. G., Boguslavsky, S. G., Grigoriev, G. N. (1968). Opening, the pilot study and development of the theory of the Lomonosov current. MGI, Academy of Sci of USSR, Sevastopol. (in Russian).Google Scholar
  19. 19.
    Kunze, E. (1990). The evolution of salt fingers in inertial wave shear. Journal of Marine Research, 48, 471–504.CrossRefGoogle Scholar
  20. 20.
    Kuzmina, N., Lee, J. H., & Zhurbas, V. (2004). Effects of turbulent mixing and horizontal shear on double-diffusive interleaving in the central and western equatorial Pacific. Journal of Physical Oceanography, 34(1), 122–141.CrossRefGoogle Scholar
  21. 21.
    Mercier, H., Arhan, M., & Lutjeharms, J. (2003). Upper-layer circulation in the eastern equatorial and South Atlantic Ocean in January–March 1995. Deep-Sea Research I, 50, 863–887.CrossRefGoogle Scholar
  22. 22.
    Metcalf, W. G., Voorhis, A. D., & Stalcup, M. C. (1962). The Atlantic equatorial undercurrent. Journal Geophysical Research, 67, 2499–2508.CrossRefGoogle Scholar
  23. 23.
    Moum, J. N., Osborn, T. R., & Paulson, C. A. (1989). Mixing in the equatorial surface layer. Journal of Geophysical Research, 94, 2005–2021. Scholar
  24. 24.
    Pacanowsky, R. C., & Philander, S. G. H. (1981). Parametrization of vertical mixing in numerical models of tropical oceans. Journal of Physical Oceanography, 11, 1443–1451.CrossRefGoogle Scholar
  25. 25.
    Rehman, F., Dhiman, M., & Singh, O. P. (2016). Effect of eigenvalue solution on the characteristics of double diffusive salt fingers. Journal of Mechanical Science and Technology, 30(6), 2557–2563.CrossRefGoogle Scholar
  26. 26.
    Schmitt, R. W. (1994). Double diffusion in oceanography. Annual Review of Fluid Mechanics, 26, 255–285.CrossRefGoogle Scholar
  27. 27.
    Schmitt, R. W., & Evans, D. L. (1978). An estimate of the vertical mixing due to salt fingers based on observations in the North Atlantic central water. Journal Geophysical Research, 83(C6), 2913–2919.CrossRefGoogle Scholar
  28. 28.
    Silva, A. C., Bourles, B., & Araujo, M. (2009). Circulation of the thermocline salinity maximum waters off the Northern Brazil as inferred from in situ measurements and numerical results. Annales Geophysicae, 27, 1861–1873.CrossRefGoogle Scholar
  29. 29.
    Stern, M. E. (1960). The salt-fountain and thermohaline convection. Tellus, 12, 172–175.Google Scholar
  30. 30.
    Stramma, L., & Schott, F. (1999). The mean flow field of the tropical Atlantic Ocean. Deep-Sea Research II, 46, 279–303.CrossRefGoogle Scholar
  31. 31.
    Turner, J. S. (1973). Buoyancy effects in fluids. Cambridge University Press:Cambridge.

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© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Shirshov Institute of OceanologyRussian Academy of SciencesMoscowRussia

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