Spatial and Temporal Dynamics of pH and Total Alkalinity of the Sea of Azov Waters in 1950–2020

V. V. Sorokina✉, V. V. Kulygin

Federal Research Centre the Southern Scientific Centre of RAS, Rostov-on-Don, Russian Federation

✉ e-mail: v.sorok@mail.ru

Abstract

Purpose. The purpose of the study consists in analyzing the spatial-temporal dynamics of pH and total alkalinity of the Sea of Azov waters in 1950–2020.

Methods and Results. Statistical analysis of the data on the Sea of Azov for 1950–2020 derived from the oceanographic database of the Southern Scientific Center of RAS made it possible to determine the average long-term values of the parameters under consideration in the Taganrog Bay, the open part of the Sea of Azov and the Kerch Strait by seasons. For the first time, the long-term changes in pH and total alkalinity of the Sea of Azov waters, as well as the distribution features of these parameters in the regions affected by the river runoffs are shown.

Conclusions. Two zones of low Alk values of seawater with the salinity ranges of 2–4 and 11–13‰ were identified in the Taganrog Bay. In these regions, under significant supersaturation of water with calcium carbonate the processes of chemogenic calcite formation are potentially possible. One zone of the increased pH values with the salinity range 4–6‰ coincides with the area of maximum phytoplankton productivity. In the Taganrog Bay, a pH increase in summer and autumn was noted, which can be explained by the growing production of organic matter against the background of salinity decrease starting from the second half of the 1970s and by a rise of water temperature in the first decade of the 2000s. The open part of the sea and the Kerch Strait are characterized by a general trend towards a decrease in pH values, except for the period of an intensive river runoff. The general pattern of Alk distribution in the Sea of Azov consists in its relatively elevated values in the Taganrog Bay (especially in the regions with salinity range of 5–8‰) which decrease towards the open sea and then increase towards the Kerch Strait. The average Alk value in the Taganrog Bay tended to decrease during the low-water periods (1972–1978 and 2011–2020) against the background of its general increase over the past seventy years. A noticeable growth of the average Alk values was noted during the period of increasing average water temperature in the Sea of Azov at the beginning of the 21st century.

Keywords

pH, total alkalinity, spatial-temporal dynamics, Sea of Azov, Taganrog Bay, Kerch Strait

Acknowledgements

The publication was prepared within the framework of the state assignment of SSC, RAS (project state registration No. 123071900007-8), Agreement No. 169-15-2023-002 (dated 01.03.2023) of the Federal Service for Hydrometeorology and Environmental Monitoring according to Agreement No. 72-223/VIPGZ-23 (dated 03.04.2023) between the IO, RAS and SSC, RAS within the framework of Consortium-2. The authors are grateful to the reviewers for their useful comments.

Original russian text

Original Russian Text © V. V. Sorokina, V. V. Kulygin, 2024, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 40, Iss. 6, pp. 821–837 (2024)

For citation

Sorokina, V.V. and Kulygin, V.V., 2024. Spatial and Temporal Dynamics of pH and Total Alkalinity of the Sea of Azov Waters in 1950–2020. Physical Oceanography, 31(6), pp. 772-787.

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