Why does increasing the dissolved CO2 concentration in seawater affect shell building in marine organisms?
Dissolving CO2 in seawater causes a suite of changes in the carbonate system in seawater: the concentrations of dissolved CO2, total dissolved inorganic carbon, and the bicarbonate ion increase, while pH, carbonate ion concentration, and calcium carbonate saturation state decrease. One or several of these changes may affect shell building in marine organisms. The formation of skeletons or shells in most marine organisms is an internal process where most organisms appear to convert bicarbonate to carbonate to form calcium carbonate. But because this conversion creates protons (hydrogen ions), the organisms must exert energy to expel the hydrogen ions into the external environment (seawater). One hypothesis as to why ocean acidification can cause slower calcification rates (and there are several) is that as seawater pH decreases, the organisms must exert more energy to rid themselves of the protons produced by calcification — they are simply working against a steeper gradient. This exp
