Hydrological factors of formation of oxygen regime of inland seas

Authors: N. Berlinsky

Year: 2018

Issue: 21

Pages: 91-97


Introduction. The regularities of the formation and dynamics of the oxygen regime in inland seas – the Black Sea and Caspian, under the influence of natural and anthropogenic factors are estimated.
Purpose. One of the features of the Black Sea is the absence of dissolved oxygen in the water below 200 meters depth. A comparison is made between the hydrological conditions of the Black Sea and the Caspian, where the depths are also quite large, but the intensity of vertical exchange is different. In addition, it is necessary to distinguish the reasons for the formation of oxygen deficient in the seas. They can be natural and human-made origin as well. The paper presents an analysis of the cause-and-effect patterns of the development of pelagial hypoxia as the examples of the Caspian and the Black Sea.
Methods. The work is the review of the problem literature that allows an assessment of the current state of gas exchange of pelagic and abyssal marine basins.
Results. Three main formation factors of the features of the hydrological structure and processes responsible for the intensity of gas exchange in the pelagic zone are identified. So, in the Black Sea, saline waters come with the Lower Bosporus Current and flow down the slope, filling the deep layers of the Black Sea basin, forming a stable vertical stratification density, that limiting vertical gas exchange. The second factor is contributing to oxygen saturation of the lower layers during the process of winter vertical circulation that is mainly expressed in the northwestern part.
The third factor is the regime shift of 1976-1978 in the Black Sea as a decrease of the winter temperature and salinity in the surface layer that led to increasing of static stability. According to actively developed convection processes, covering the entire body of the Caspian Sea, in contrast to the Black Sea, there is an intensive exchange between the upper and the deep layers and the intensity of convection depends on the temperature regime of the year. In the Caspian Sea, the regime shift of 1976-1978 led to a twofold increase in the static stability of water below 100 m, the almost complete cessation of the ventilation of the deep waters of the (the process the slope cascading) and the extreme decrease in the concentrations of dissolved oxygen.
Conclusion. In the Black Sea, the formation of a stable of the density vertical stratification is due to the intrusion of saline dense waters of the Lower Bosporus Current, and the winter vertical circulation is expressed only in the northwestern part of the sea, which generally limits vertical gas exchange with the deep water. In the Caspian Sea, convective mixing plays a main role in the formation of the hydrological structure of water and the ventilation of the bottom layers. In cold winters in the northern Caspian, strong cooling, as well as salinity during ice formation, creates the conditions for the formation of waters with a density that allows them to flow down the slopes of  the bottom along isopycnic surfaces and aerating the deep layers of the sea.

Tags: Black and Caspian Sea; hydrological structure; oxygen regime; pelagic; гідрологічна структура; Каспійське море; кисневий режим; пелагіаль; Чорне море


  1. Baydin, S.S., Kosarev, A.N. (Eds). (1986). Kaspiyskoe more. Gidrologiya i gidrokhimiya [The Caspian Sea. Hydrology and hydrochemistry]. Moscow : Nauka. (in Russ.)
  2. Berlinskiy, N.A. (2012). Dinamika tekhnogennogo vozdeystviya na prirodnye kompleksy ust’evoy oblasti Dunaya. [Dynamics of technogenic impact on natural complexes of the mouth area of the Danube]. Odessa. Astroprint. (in Russ.)
  3. Il’in, Yu.P. et al. (2012). Gidrometeorologicheskie usloviya morey Ukrainy T. 2. Chernoe more [Hydrometeorological conditions of the seas of Ukraine. Vol. 2. Black Sea]. Sevastopol. (in Russ.)
  4. Tuzhilkin, V.S. (2008). Sezonnaya i mnogoletnyaya izmenchivost’ termokhalinnoi struktury vod Chernogo i Kaspiyskogo morey i processy ee formirovaniya [Seasonal and long-term variability of the thermohaline structure of the waters of the Black and Caspian seas and the processes of its formation]. Abstract of Dr. Geogr. Sc. dissertation, Moscow State Un-ty, Moscow. (in Russ.)
  5. Berlinskiy, N.A. (1989). [Mechanism of formation of benthic hypoxia in shelf ecosystems]. Vodnye resursy [Water resources], 4, 112-121. (in Russ.)
  6. Berlinskiy, N.A., Dykhanov, Yu.M. (1991). [To the problem of formation of bottom hypoxia in the northwestern part of the Black Sea]. Ekologiya morya [Sea Ecology], 38, 11-15. (in Russ.)
  7. Berlinskiy, N.A., Kosarev, N.A., Bogatova, Yu.I., Garkavaya, G.P. (2004). [The influence of the Danube on the ecological conditions of the northwestern part of the Black Sea]. Vestnik MGU [Bulletin MSU], 5, 17-21 (in Russ.)
  8. Belevich, R.R., Orlova, I.G. (1996). [Features of the interannual variability of hydrological and hydrochemical characteristics of waters on the north-western shelf of the Black Sea in recent decades (60-90s)]. Morskoy gidrofizicheskiy zhurnal [Marine Hydrophysical journal], 02, 62-73. (in Russ.)
  9. Berlinskiy, N.A., Tuzhilkin, V.S., Kosarev, A.N., Nalbandov, Yu.R. (2006). [Variability of hydrophysical fields and benthic hypoxia]. In: Zaytsev, Yu.P., Aleksandrov, B.G., Minicheva, G.G. (Eds). Severo-zapadnaya chast’ Chernogo morya: biologiya i ekologiya [North-western part of the Black Sea: biology and ecology]. Kiev: Naukova dumka, ch. I (in Russ.)
  10. Berlinsky, N., Bogatova, Yu., Garkavaya, G. (2006). Estuary of the Danube. In: Wangersky, P.J. (Ed.). The Handbook of Environmental Chemistry. Berlin-Heidelberg: Springer-Verlag, vol.5, pp. 233-264.
  11. Skorohod, A.I. (1996). Osobennosti solevogo sostava vod Kaspiyskogo morya [Features of the salt composition of the waters of the Caspian Sea]. Abstract of Cand. Geogr. Sc. dissertation, Moscow State Un-ty, Moscow. (in Russ.)
  12. Belov, A.A. (2004). Issledovanie izmeneniy gidrohimicheskoy struktury Kaspiyskogo morya za poslednie 70 let [Research of changes in the hydrochemical structure of the Caspian Sea over the past 70 years]. Abstract of Cand. Geogr. Sc. dissertation, Moscow State Un-ty, Moscow. (in Russ.)
  13. Blatov, V.S., Bulgakov, N.P., Ivanov, V.A., Kosarev, A.N., Tuzhilkin, V.S. (1984). Izmenchivost’ gidrofizicheskikh poley Chernogo morya [Variability of the hydrophysical fields of the Black Sea]. Leningrad: Gidrometeoizdat.
Download full text (PDF)