Features of interdecademy variability of the oxygen regime in the spring season in the Black Sea

by

A.A. Valle

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

E – mail: ogorodovaa.a@mail.ru

DOI: 10.33075/2220-5861-2022-3-5-11

UDC 551.465 (262.5)                                                      

Abstract:

   The article considers the oxygen regime of the Black Sea, which is an important indicator of the general state of the sea ecosystem. Based on archival observational data from 1923 to 2022, the interdecadal variability of dissolved oxygen is analyzed separately in the deep-water and northwestern parts of the Black Sea. The analysis was carried out only for the spring season (April–June) at the horizons of 0, 10, 20, 40 and 50 m on a multi-year scale with a characteristic time scale of several tens of years.

   Based on the results of this work, it is concluded that the photosynthetic activity of aquatic plants plays a significant role in the enrichment of water with oxygen. In spring, with increasing temperature, the intensity of turbulent mixing of the active layer decreases, and photosynthetic aeration becomes the main source of oxygen in the water column. This can be clearly seen on an interdecadal scale, with depth, the oxygen concentration in the deep part in the spring increases due to the photosynthetic enrichment of water with oxygen, and in the northwestern part, the highest oxygen concentrations are found on the surface, so the river runoff most likely has a great influence on the oxygen content. It is shown that from 1989 to 2009. there was a sharp decrease in the average ten-day content of dissolved oxygen (by more than 90 µM). Such a sharp decrease in oxygen content seem to be related to eutrophication in the deep part of the sea in the late 1980s and early 1900s.

Keywords: oxygen regime, northwestern part of the Black Sea, deep water part.

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