Seasonal variability of CO₂ content in the surface layer of the Black Sea waters and the intensity of exchange with the atmosphere according to biogeochemical reanalysis data

Е. M. Lemeshko*, M. V. Tsyganova, Е. E. Lemeshko

Marine Hydrophysical Institute of RAS, Sevastopol, Russia

* e-mail: evgeny.lemeshko@mhi-ras.ru

Abstract

This article examines the seasonal and interannual spatial variability of the equilibrium partial pressure of carbon dioxide pCO₂ in the surface water layer and the carbon dioxide flux FCO₂ at the atmosphere-sea interface for the Black Sea based on biogeochemical reanalysis data. In situ measurements for 2015–2024 were used to validate the reanalysis data and compare the seasonal variations of pCO₂ and FCO₂. Additionally, pCO₂ from reanalysis data in the surface layer of the atmosphere was compared with instrumental measurements. Seasonal cycles of the polygon-averaged FCO₂ flux and the equilibrium partial pressure in the near-surface layer of the sea, based on instrumental observations and biogeochemical reanalysis data, coincide within 95% confidence intervals, with the exception of the summer season for pCO2. Statistically significant regression relationships (p<0.001) were established between the parameters under consideration. As a result, the reanalysis data provided new insights into the seasonal variability of pCO₂ and FCO₂ throughout the sea area. This is particularly relevant when observational data are lacking for the winter and spring periods and the expedition area is limited. Seasonal variability of pCO₂ and FCO₂ is primarily influenced by water temperature and the difference in partial CO₂ pressure between the sea and the atmosphere. The distribution of pCO₂ and FCO₂ on the shelf and in the coastal zone of the sea demonstrates the significant influence of upwellings near Crimea and river plumes on the seasonal dynamics of FCO₂.

Keywords

carbon dioxide partial pressure, pСО₂, carbon dioxide flux, FСО₂, seasonal cycle of pСО₂, seasonal cycle of FСО₂, water temperature, salinity, plume, upwelling, Black Sea, regional climate СО₂

Acknowledgments

This work was carried out under the state assignment of the Federal Research Center “Marine Hydrophysical Institute of the RAS” on topic FNNN-2024-0016 “Study of spatio-temporal variability of oceanological processes in the coastal, coastal and shelf zones of the Black Sea under the influence of natural and anthropogenic factors based on contact measurements and mathematical modeling” (code “Coastal Research”).

About the authors

Evgeny M. Lemeshko, Leading Researcher, Marine Hydrophysical Institute of RAS (2 Kapitanskaya St., Sevastopol, 299011, Russia), PhD (Phys.-Math.), ORCID ID: 0000-0003-4676-1940, ResearcherID: S-7815-2018, evgeny.lemeshko@mhi-ras.ru

Marina V. Tsyganova, Junior Researcher, Marine Hydrophysical Institute of RAS (2 Kapitanskaya St., Sevastopol, 299011, Russia), ORCID ID: 0000-0003-2398-1756, ResearcherID: S-5426-2018, m.tsyganova@mhi-ras.ru

Egor E. Lemeshko, Researcher, Marine Hydrophysical Institute of RAS (2 Kapitanskaya St., Sevastopol, 299011, Russia), PhD (Geogr.), ORCID ID: 0000-0001-5612-000X, ResearcherID: C-5691-2016, Scopus Author ID: 57205681264, e.lemeshko@mhi-ras.ru

For citation

Lemeshko, Е.M., Tsyganova, M.V. and Lemeshko, Е.E., 2026. Seasonal Variability of CO₂ Content in the Surface Layer of the Black Sea Waters and the Intensity of Exchange with the Atmosphere According to Biogeochemical Reanalysis Data. Ecological Safety of Coastal and Shelf Zones of Sea, (3), pp. 38–55.

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