Dissolved inorganic carbon has a nutrient-like vertical profile due to uptake by phytoplankton. Concentrations are lowest in the Atlantic, where deep water sinks into the ocean depth, and higher in the deep waters of the Pacific as POC sinks into the deep-sea and is remineralized to DIC.
The titration alkalinity values increase as deep water flows along the conveyor. The increase in TAlk is driven, primarily, by dissolution of calcium carbonate shells sinking through the water column. The changes in TCO2 and TAlk drive large changes in the concentrations of(CO2), (HCO3-) and (CO32-), which are all chemical species of inorganic carbon.
Carbon exists in seawater as dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) and particulate inorganic carbon (PIC). The DIC consists of carbon dioxide (CO2), bicarbonate (HCO3-) and carbonate (CO32-), which can interchange rapidly with each other to maintain chemical equilibrium (Johnson, 1982). The total amount of inorganic carbon is called TCO2. Seawater is slightly alkaline due to bases such as bicarbonate and carbonate. A measure of the basicity of seawater is the Titration Alkalinity (TAlk) = (HCO3-) + 2x(CO32-) + (B(OH)4-) + (OH-) - (H+). If TCO2 and TAlk are measured, then the concentration of the individual components can be calculated.