Features of seasonal variability of hydrological and hydrochemical characteristics of subsurface waters of the northwestern Black Sea

by

A.A. Valle, A.B. Polonsky

 Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28

E-mail: ogorodovaa.a@mail.ru

DOI: 10.33075/2220-5861-2021-2-7-15

UDC 551.465 (262.5)

Abstract:

   In our work, based on the archival data of observations carried out in 1955 – 2015,  hydrological and hydrochemical characteristics in the 10–30 m layer in the northwestern shelf (NWS) of the Black Sea, including the Danube estuary area are analyzed.  Intra-annual changes in dissolved oxygen and water temperature in the NWS and in the Danube estuary area are shown to have a well-pronounced seasonal character. Water temperature in the estuary area of the Danube is characterized by lower values in all seasons than in the NWS. Salinity at the horizons of 10 and 20 m in winter in the estuary area of the Danube is lower than in the NWS due to the freshening of the upper mixed layer by river runoff. In spring, resulting from increased river runoff, an increase in the stability of water stratification occurs, which prevents the spread of heat inland and vertical exchange of oxygen. The strongest freshening in the studied layer is established at the horizon of 10 m. In spring, the southerly winds “trap” river waters in the shallower part of the shelf, and westerly winds give rise to the spread of freshened waters to the east. The summer-autumn period is characterized by low intensity of vertical and horizontal water exchange, which reduces the flow of oxygen to the subsurface layers.

   Harmonic analysis shows that in the Danube estuary area and in the NWS,  the annual signal is dominant for temperature, salinity and oxygen, except for salinity at the 30 m horizon in the estuary area of the Danube. The semiannual harmonic of salinity at 30 m in the estuarine area of the Danube is most likely related to both limited data availability and their noisiness.

Keywords: temperature, salinity, oxygen regime, northwestern part of the Black Sea, near the mouth of the Danube.

To quote: Valle, A.A., and A.B. Polonsky. “Features of Seasonal Variability of Hydrological and Hydrochemical Characteristics of Subsurface Waters of the Northwestern Black Sea.” Monitoring Systems of Environment no. 2 (June 24, 2021): 07–15. doi:10.33075/2220-5861-2021-2-7-15.

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