Purpose. Global changes in the ocean biogeochemical structure are mostly pronounced on a regional scale. They are caused by the increased carbon flux to the aquatic ecosystems that is a result of its growing emission from the atmosphere, coastal sinks as well as and the primary production and degradation processes taking place in marine environments. It seems reasonable to separate the enumerated sources to the natural climatic factors and the anthropogenic ones which are considered in the studies of a carbon cycle. To assess the quantitative characteristics of the factor leading to natural carbon cycle transformation, it is necessary to reconstruct its budget, which is governed by the carbon intake and removal, as well as by the processes resulting in its redistribution between various forms. Methods and Results. The carbon budget in the Sevastopol Bay ecosystem (the Black Sea) is assessed, and contribution of the anthropogenic component is analyzed based on the long-term research (2007-2018) of hydrochemical and geochemical characteristics. The following results of the sediment carbonate system studies, namely the vertical profile of dissolved inorganic carbon (DIC), total alkalinity (ТА) and pH, and the dissolved inorganic carbon and alkalinity ratio show that the organic matter oxidation occurs mainly under the anaerobic conditions. It has been also revealed that the dissolved inorganic carbon flux (J DIC ) at the "water -sediment" boundary is directed from sediments to the bottom waters and amounts 0.42-0.61 mol•m -2 •year -1 . Conclusions. Different components of the inorganic carbon budget showed that the anthropogenic sources were the most important: their contribution constituted not less than 75% of the total inorganic carbon inflow. Based on the value of the dissolved inorganic carbon total reserve and its removal to the open sea, the time of complete renewal of the Sevastopol Bay waters is assumed to be 2 years and 4 months.

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