Abstract
Carbonic acid formed by the dissolution of CO2 in seawater dissociates to yield hydrogen carbonate, carbonate, and hydrogen ions, which are linked to each other by dissociation constants and constitute the marine CO2 system. To determine the composition of the CO2 system, requires that the values of two of four measurable variables are known: total CO2 (sum of the CO2 species), alkalinity (excess of base equivalents over hydrogen ions), pH (log of the hydrogen ion concentration), and the CO2 partial pressure (pCO2 in air at equilibrium with the respective water). Alkalinity plays a central role because it controls the status of the CO2 system in case that the sea is at equilibrium with CO2 in the atmosphere. In the Baltic Sea, alkalinity inputs via river water are subject to strong regional differences. Together with the alkalinity input by inflowing North Sea water different alkalinity regimes are formed which lead to characteristic regional distributions of the total CO2 and pH. Alkalinity also affects the relationships between the variables of the CO2 system. The magnitude of the change in pCO2 in response to a change in total CO2 increases with decreasing alkalinity. This effect is important when pCO2 measurements are used to estimate biological production, but it also influences CO2 gas exchange with the atmosphere, by increasing the equilibration time at high alkalinities.
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Schneider, B., Müller, J.D. (2018). The Marine CO2 System and Its Peculiarities in the Baltic Sea. In: Biogeochemical Transformations in the Baltic Sea. Springer Oceanography. Springer, Cham. https://doi.org/10.1007/978-3-319-61699-5_2
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DOI: https://doi.org/10.1007/978-3-319-61699-5_2
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