Oceanological Studies of the Russian Sectors of the Baltic Sea in 2023

Environmental monitoring of the Russian sectors of the Baltic Sea was continued through three expeditions in 2023: cruise 55 of the R/V Akademik Sergei Vavilov (April) and cruises 54 and 55 of the R/V Akademik Boris Petrov (November and December, respectively). Seasonal quantitative estimates of hydrological–hydrochemical and hydrobiological parameters and carbon dioxide fluxes at the water–air interface were obtained, and the geological and geomorphological conditions of the study areas were refined. The influence of the Neva River on the eastern Gulf of Finland was stable in all seasons and could be traced at a distance of up to 30 nautical miles from Neva Bay. The Southeastern Baltic bottom layer experienced extensive hypoxia and mosaic euxinia. Significant aeration of bottom waters occurred in December due to the combined influence of seasonal convection and downwelling resulting from a series of storms. In both study areas, high values of integral primary production were obtained in April, which were two orders of magnitude higher than the December values. The concentration of chlorophyll a, accordingly, differed by an order of magnitude. The Gulf of Finland was an emitter of carbon dioxide into the atmosphere, especially in April, while the Southeastern Baltic absorbed carbon dioxide in April and was a zone of weak emissions in November and December.