We provide an expert quality assessment of the data for 1932 1993 and used these data to perform the numerical analysis of the carbonate system of the aerobic zone in the Black Sea. The intraannual and long-term variations of the carbonate system are studied in the abyssal part of the sea for 1960-1993. We propose explanations of the intraannual variations of the analyzed system for various layers of the aerobic zone and reveal long-term variations of the pH values, total alkalinity, and the ratios of the components of the carbonate system. We discover and explain the observed increase in the concentrations of 2 and 2 and the partial pressure of carbon dioxide 2 , as well as a decrease in values and the concentration of 3 2-in waters of the aerobic zone of the Black Sea.The carbonate system is the sum of all inorganic forms of carbon and represents the most important component of the total budget and turnover of carbon in marine media, i.e., of one of the main cycles of the turnover of substances in nature. In seawater, the inorganic carbon has three different forms, namely, carbon dioxide CO 2 (aq) dissolved in seawater, bicarbonate HCO 3 , and carbonate-ions CO 3 2 .The carbonate system is probably the most complicated biogeochemical system of the sea. It is described by the following equations of chemical equilibrium [1, 2]: CO 2 (g) + nH 2 O CO 2 nH 2 O(H 2 CO 3 , CO 2 (aq))where the concentration of CO 2 is determined according to the Henry law [CO 2 ] = K 0 (T , S)pCO 2 (2) and K 0 is the coefficient of solubility of CO 2 in seawater, CO 2 (aq)
UDC 551. 465(262.5) We analyze the components of the carbon system of the Sevastopol bay waters and the balance of main sediment-forming substances using the data of field investigations in 1998-2008. The interannual variations of total inorganic carbon and the equilibrium partial pressure of carbon dioxide in the bay water are noted. An increase in the flux of carbon dioxide into the bay and in the content of organic carbon in bottom sediments is revealed, and an explanation of this phenomenon is given. The priority accumulation of organic carbon in the sediments of the bay is established. We assess the interannual variation in the relative abundances of organic and inorganic carbon as an index of the carbon cycle stability.Keywords: carbon cycle, components of the carbon system, Sevastopol bay.Coastal water areas are the zones of interaction of land, sea, and atmosphere. This is exactly the place where the main biogeochemical processes (the formation of primary production, respiration, transformation of organic carbon into inorganic carbon, deposition and burial of carbon, and interaction and substance exchange with the land and atmosphere) run most intensively.The biogeochemical cycles of coastal ecosystems are subject, first of all, to increasing anthropogenic pressure, especially due to the huge amount of organic carbon and nutrients coming from the land. As compared with preindustrial times, the amount of nitrogen coming to the water as a result of human activity has increased by a factor of five [1]. It was shown in [2, 3] that the inflow of phosphorus to the ocean is approximately twice as high as in preindustrial times. The increase in the concentration of carbon dioxide in atmosphere by more than 20% for the last 200 years [4] caused a transformation of the carbon cycle in coastal water areas: in coastal regions, a decrease in pH was recorded and a significant increase in the content of dissolved carbon dioxide was observed [3,[5][6][7][8].The Sevastopol bay, which was chosen as the object of investigation, is a notable example of a coastal water area subject to permanently increasing anthropogenic pressure for the last two centuries. It is a semiclosed water area of the estuary type. Its length from the entry to the tip is ~7 km, the maximum width is ~1 km, and the mean depth is 12 m. The surface area of the bay is 7.96 km 2 . After the construction of a protective pier in 1977-1978, the entry width decreased from 940 to 550 m, which caused significant changes in the characteristics of water exchange. On the average per year, it decreased by 40-70%, and the duration of the "full" water exchange in the bay increased almost twice [9].The state of the carbon cycle and its components in the Sevastopol bay was studied earlier in a number of works [10][11][12][13][14], and the sinks and sources of carbon dioxide in the bay were discussed in our works [15][16][17].The purpose of the present work is to study the long-term dynamics of components of the carbon system of waters and the contents of organic and ...
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