PROCESSES THAT DETERMINE THE pH OF SEAWATER
The pH of seawater is dependent on shifts in the autoprolysis of hydrogen carbonate
2 HCO3-= CO2 + H2O + CO32-
caused by the production and decomposition of planktonic maiter. Using stoichiometric relationships and mean concentrations of nitrate and phosphate it is shown that surface seawater will have a pH close to 8 at 15°C on the seawater medium scale. A figure shows the dependence of the in situ pH on the difference between the titration alkalinity (At) and total inorganic carbonate (Ct). Another figure shows Ct in surface seawater as a function of the partial pressure of carbon dioxide in the atmosphere. Minor protolytes adjust themselves to the carbonate system and seawater medium. In the case of boric acid-borate in surface seawater it is shown that B(OH)4- accounts for 5 % of At.