Superoxide, produced photochemically as well as microbially, is an important reactant present in seawater and a major source of hydrogen peroxide. Superoxide decay may occur through catalyzed or uncatalyzed dismutation forming H 2 O 2 and O 2 , through oxidation to O 2 , or through reduction into H 2 O 2. Under definite circumstances, the redox processes that are different from dismutation could produce or consume H + , thereby altering the pH of seawater. In order to alter the pH, these processes have to involve, together with O 2 , redox couples that exchange e and H + in a ratio other than 1:1. This potential pH modification is dependent on several factors, including the extent of H + imbalance, the rate of formation/transformation of superoxide (which reaches a steady-state concentration in seawater), and the alkalinity of seawater (which varies globally from 2.10 to 2.45 mmol L 1 and buffers the pH variations). In the present study, an estimate of the possible pH changes associated with photochemically-produced superoxide in the global ocean has been provided. Among the important approximations that were required to perform the calculations, one