Oral

IAPSO

P02 - Physics and Biogeochemestry of Semi-Enclosed, Shelf Seas and Coastal Zones

Seasonal variability of carbon dioxide flux on the coastal zone of the Black Sea

The oceans are regarded as the primary natural reservoir capable of absorbing excess CO2 from the atmosphere, with estimates suggesting that since the onset of the industrial era, the oceans have already absorbed approximately one-third of anthropogenic carbon emissions. It is noteworthy that the ocean possesses not only the capacity to absorb carbon dioxide from the atmosphere, but also, under specific conditions, the potential to act as a source of carbon dioxide. The flux of CO2 between the ocean and the atmosphere can vary depending on the partial pressure of pCO2 in the atmosphere, season, time of day, biological and hydrophysical conditions. The hydrochemistry of coastal areas differs from that of deep-water (open/central) areas. This is due to rapid variability and a large number of factors influencing the formation of hydrochemical characteristics of coastal waters. Among the factors contributing to this phenomenon are high productivity, the presence of surface and underground freshwater runoff from the mainland, as well as vertical mixing (due to the shallow depth) and a significant increase in the anthropogenic load. Against this background, shifts in the equilibrium of the carbonate system of waters are already being observed in the coastal part of water areas, with an increase in pCO2 in water and, as a consequence, a decrease in pH value. Since 2022, continuous studies of carbon dioxide flux, carbonate system parameters and phytoplankton dynamics have been conducted in the Black Sea (Gelendzhik district, north-eastern part of the coast).The aim of the project is to assess the quantitative values and direction of carbon dioxide flux in different seasons and on an annual scale, as well as to identify the role of biotic and abiotic factors in this process. The research involves the daily collection and analysis of samples, including pH and total alkalinity, phytoplankton abundance, biomass and species composition. Additionally, surface water temperature and salinity, wind speed and direction, and atmospheric carbon dioxide concentration are measured. The obtained data facilitate the calculation of the carbon dioxide flux, as well as synchronous analyses with the primary factors contributing to its variability. The seasonal dynamics of the biological carbon pump demonstrated that, from February to August 2024, the organic pump was predominantly operational, with the carbonate pump exhibiting negligible activity during this period. Consequently, the water area of the polygon functioned as a source of CO2 emissions to the atmosphere in 2024. The primary factor contributing to this phenomenon was the substantial excess of pCO2 in the water relative to the atmospheric equilibrium, a consequence of the operation of the biological carbon pump. The research was carried out within the framework of the state assignment of the Institute of Oceanology FMWE-2023-0001.