Study of the effects of Ekman dynamics in the bottom boundary layer on the Black Sea continental slope

A G Zatsepin; V V Kremenetskiy; O I Podymov; A G Ostrovskii

doi:doi:10.2205/2020ES000693

Study of the effects of Ekman dynamics in the bottom boundary layer on the Black Sea continental slope

Published в Russian Journal of Earth Sciences · Volume 20, Issue 1, 2020 · Pages 1–16 · Rubrics: ORIGINAL ARTICLES

DOI 10.2205/2020ES000693

Received: 25.02.2020 Accepted: 25.02.2020 Published: 25.02.2020 Language of publication: ENG

Authors

A G Zatsepin ¹ · V V Kremenetskiy ² · O I Podymov ³ · A G Ostrovskii ⁴

1 Shirshov Institute of Oceanology, Russian Academy of Sciences

2 Shirshov Institute of Oceanology, Russian Academy of Sciences

3 Shirshov Institute of Oceanology, Russian Academy of Sciences

4 Shirshov Institute of Oceanology, Russian Academy of Sciences

ABSTRACT

A possible ventilation mechanism of the aerobic zone in the Black Sea may exist, caused by a descent of oxygen-containing water down the bottom slope in the Ekman boundary layer. To study this theory three long-term (1.5-2 months) installations of automatic bottom stations were carried out in 2018-2019 on the Black Sea shelf/continental slope in the depth range from 80 to 243 m. The stations were placed on a coastal cross section on the beam of the Tolstyi Cape (the Gelendzhik Bay). They recorded the hydrophysical (temperature and salinity of water, pressure and flow rate) and hydrochemical (dissolved oxygen concentration) parameters at 0.5-2.5 m from the bottom. The acquired data were used to estimate the spatiotemporal scales of water transfer in the bottom layer along the slope. Our analysis had confirmed the existence of the bottom water transport normal to the shore. A downward flow was observed in the case of an intensive north-western alongshore current. This type of water movement corresponds to both the geostrophic adjustment and the dynamics of the bottom Ekman boundary layer. However, changes in water density in the bottom layer, which occur due to the water movement up and down the slope, were of the same range as those observed in the water column at the same depth. This fact casts doubt on the efficiency of the Ekman transport in the bottom layer as the ventilation mechanism for water of the upper continental slope of the Black Sea.

KEYWORDS

Black Sea shelf-slope zone northwestern current bottom boundary layer downward Ekmantransport water oxygen ventilation

Information References

Authors:

1. Shirshov Institute of Oceanology, Russian Academy of Sciences

2. Shirshov Institute of Oceanology, Russian Academy of Sciences

3. Shirshov Institute of Oceanology, Russian Academy of Sciences

4. Shirshov Institute of Oceanology, Russian Academy of Sciences

Type:

Article

Pages:

from 1 to 16

Status:

Published

Language:

English

Keywords:

Black Sea, shelf-slope zone, northwestern current, bottom boundary layer, downward Ekmantransport, water oxygen ventilation

Funding

The study was fulfilled within the framework of the Russian state program No. 0149-2019-0004, supported in part by the Russian Foundation for Basic Research (project No. 17-05-00381).

References

1. Dickey, T. D., J. C. Van Leer (1984) , Observations and simulation of a bottom Ekman Layer on a continental shelf, J. Geophys. Res., 89, no. C2, p. 1983-1988, https://doi.org/10.1029/JC089iC02p01983

2. Elkin, D. N., A. G. Zatsepin, A. G. Ostrovskii, et al. (2017) , Sinking of less dense water in the bottom Ekman layer formed by a coastal downwelling current over a sloping bottom, Oceanology, 57, no. 4, p. 531-537, https://doi.org/10.1134/S0001437017040051 DOI: https://doi.org/10.7868/S0030157417040025; EDN: https://elibrary.ru/ZCRXWP

3. Garrett, C., P. MacCready, P. B. Rhines (1993) , Boundary mixing and arrested Ekman layers: rotating stratified flows near a sloping boundary, Ann. Rev. Fluid Mech., 25, p. 291-323, https://doi.org/10.1146/annurev.fl.25.010193.001451

4. Kushnir, V. M. (2007) , Bottom boundary layer in the Black Sea: experimental data, turbulent diffusion, and fluxes, Oceanology, 47, no. 1, p. 33-41, https://doi.org/10.1134/S0001437007010067 EDN: https://elibrary.ru/XLNPTN

5. MacCready, P., P. B. Rhines (1993) , Slippery boundary bottom layers on a slope, Phys. Oceanography, 23, no. 1, p. 5-22, https://doi.org/10.1175/1520-0485(1993)023%3C0005:SBBLOA%3E2.0.CO;2

6. Ostrovskii, A. G., A. G. Zatsepin (2016) , Intense ventilation of the Black Sea pycnocline due to vertical turbulent exchange in the Rim Current area, Deep-Sea Res. I, 116, p. 1-13, https://doi.org/10.1016/j.dsr.2016.07.011 EDN: https://elibrary.ru/WVZLUZ

7. Perlin, A., J. N. Moum, J. M. Klymak, et al. (2005) , A modified law-of-the-wall applied to oceanic bottom boundary layers, J. Geophys. Res., 110, p. C10S10, https://doi.org/10.1029/2004JC002310

8. Perlin, A., J. N. Moum, J. M. Klymak, et al. (2007) , Organization of stratification, turbulence, and veering in bottom Ekman layers, J. Geophys. Res., 112, p. C05S90, https://doi.org/10.1029/2004JC002641

9. Plaksina, M. O., A. M. Pigolkina, D. N. Elkin, et al. (2015) , Gravity current at a sloping bottom in a lineary stratified fluid, Proceedings of the 18th International Conference "Fluxes and Structures in Fluids" A. Ishlinsky institute for problems in mechanics of the RAS, p. 172-175, Kaliningrad State Technical University, Kaliningrad

10. Pollard, R. T., P. B. Rhines, R. O. R. Y. Thompson (1973) , The deepening of the wind mixed layer, Geophys. Fluid Dyn., 3, p. 381-404, https://doi.org/10.1080/03091927208236105

11. Schaeffer, A., M. Roughan, B. D. Morris (2013) , Cross-shelf dynamics in a Western Boundary Current regime: implications for upwelling, J. Phys. Oceanography, 43, no. 5, p. 1042-1059, https://doi.org/10.1175/JPO-D-14-0091.1

12. Stunzhas, P. A., M. B. Gulin, E. A. Ivanova, et al. (2018) , Study of oxygen regime in the near-bottom water layer and reaction of zoobenthos to hypoxia/anoxia at the contact zone of the Black Sea chemocline with continental slope, Some Results of Integrated Coastal Expedition "The Black Sea" Carried out on RV "Ashamba", p. 141-145, Nauchnyi Mir, Moscow (In Russian) DOI: https://doi.org/10.29006/978-5-91522-472-7-2018.7; EDN: https://elibrary.ru/VLXTRV

13. Stunzhas, P. A., M. B. Gulin, A. G. Zatsepin, et al. (2019) , On the possible presence of oxygen in the upper sediment layer of the hydrogen sulfide zone in the Black Sea, Oceanology, 59, no. 1, p. 155-157, https://doi.org/10.1134/S0001437019010211 EDN: https://elibrary.ru/DRQMJA

14. Taylor, J. R., S. Sarkar (2008) , Stratification Effects in a Bottom Ekman Layer, J. Phys. Oceanogr., 38, p. 2535-2555, https://doi.org/10.1175/2008JPO3942.1 EDN: https://elibrary.ru/WNBXIH

15. Weatherly, G. L. (1972) , A study of the bottom boundary layer of the Florida current, J. of Phys. Oceanogr., 2, no. 1, p. 54-72, https://doi.org/10.1175/1520-0485-2.1.54

16. Weatherly, G. L., P. J. Martin (1978) , On the structure and dynamics of the oceanic boundary layer, J. of Physical Oceanography, 8, no. 4, p. 557-570, https://doi.org/10.1175/1520-0485(1978)008%3C0557:OTSADO%3E2.0.CO;2

17. Zatsepin, A. G., N. N. Golenko, A. O. Korzh, et al. (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, no. 3, p. 301-312, https://doi.org/10.1134/S0001437007030022 EDN: https://elibrary.ru/KHBUXG

18. Zatsepin, A. G., A. G. Ostrovskii, V. V. Kremenetskiy, et al. (2013) , On the nature of short-period oscillations of the main black sea pycnocline, submesoscale eddies, and response of the marine environment to the catastrophic shower of 2012, Izvestiya. Atmospheric and oceanic physics, 49, no. 6, p. 659-673, https://doi.org/10.1134/S0001433813060145 EDN: https://elibrary.ru/SLHDMN

19. Zhurbas, V. M., I. S. Oh, T. Park (2006) , Role of the beta-effect in the decay of the alongshore baroclinic jet associated with transient coastal upwelling and downwelling: numerical experiments, Oceanology, 46, no. 2, p. 170-177, https://doi.org/10.1134/S0001437006020032 EDN: https://elibrary.ru/LJRTDP

Study of the effects of Ekman dynamics in the bottom boundary layer on the Black Sea continental slope

Confirmation

Регистрация