Processes controlling carbon dioxide in seawater

Although the solution chemistry of carbon dioxide (CO₂) in seawater has been extensively studied during the past century, many questions still persist regarding the ecological understanding of the observed variability of the measured CO₂ parameters; pH, fugacity of CO₂ (fCO₂), dissolved inorganic carbon (DIC) and total alkalinity (TA). At equilibrium, these four measurable parameters combined with the proper apparent equilibrium constants for carbonic acid in seawater describe the speciation concentrations of dissolved aqueous CO₂ (CO₂*(aq)), bicarbonate (HCO₃−) and carbonate (CO ₃2−). The observed variability of the measured CO₂ parameters within the environment must be interpreted within the proper framework of assumptions relating the solution chemistry to the physical, chemical and biological processes that alter CO₂ concentrations. This requires a cross discipline understanding of the effects of biology and physics on the CO₂ solution chemistry in seawater.; Photosynthesis alters seawater CO₂ chemistry by reducing dissolved aqueous CO₂ to organic matter. This results in a decrease of fCO ₂ pressure and DIC concentration. Temperature alters seawater CO ₂ chemistry through changes of the equilibrium constants that determine the partitioning of the inorganic carbon species; dissolved aqueous CO ₂, bicarbonate and carbonate. The interaction of these two processes on timescales of seconds to years is a major theme of this dissertation. Additionally, the timescale of exchange for CO₂ across an atmosphere-seawater interface can greatly influence the interpretation of observations within natural settings.; The interaction of these processes was studied in three contrasting systems to illustrate the similarities and differences, and to reveal an unexpected complexity. For instance, the observed decrease of normalized DIC (to a salinity of 35) at Station ALOHA within the North Pacific Subtropical Gyre was the result of the thermodynamic control on the solution chemistry of CO₂ in seawater. In the region west of the Antarctic Peninsula, CO ₂ dynamics were a function of temperature changes and dilution due to ice melt, as well as net photosynthesis. Finally, CO₂ chemistry was studied in a temperature-controlled continuous culture. Many results from such studies are applied to open ocean process yet these studies may be flawed because of improper assumptions concerning gas-solution equilibrium and thermodynamic equilibrium.