TEAM GE-C
HOW OCEAN ACIDIFICATION OCCURS
Generally, the exchange of carbon dioxide between air and ocean is relatively fast, and take place on a time scale of months to a year. So, the concentration of carbon dioxide in surface seawater is approximately at equilibrium, because the marine carbonate buffer system allows the ocean to uptake carbon dioxide exceed from its capacity based on solubility. This solubility controls the pH of the ocean. This control is achieved by the change the form of inorganic carbon.
First, when carbon dioxide is dissolved, it react with water to form carbonic acid. And carbonic acid dissociates into a hydrogen ion (H+) and bicarbonate ion (HCO3-). Also, some of hydrogen ion (H+) react with carbonate to form another bicarbonate ion.
CO2 + H2O -> H+ + HCO3- -> 2H+ + CO32-
CO2 + H2O + CO32- -> HCO3- + H+ + CO32- -> 2HCO3-
The increase in dissolved carbon dioxide concentration decreases the pH and shifts the equilibrium of inorganic carbon species in seawater, resulting in an increase in carbon dioxide and carbonic acid.
In other words, when the amount carbon dioxide of ocean absorption increased, because of anthropogenic sources such as fossil fuel emission, cement production and deforest, there can be increase in H+ and HCO3- but reduction in CO32-.
Typical concentrations of the major weak acids and weak bases in seawater as a function of pH. This diagram is calculated for constant dissolved inorganic carbon (DIC) and constant total boric acid using constants from Dickson et al. (2007) and Lueker et al. (2000).
As you can see in the graph, at the lower level of pH, about 6 to 7, there exist low concentration of carbonate. This decrease in bicarbonate ion reduces the overall buffering capacity as CO2 increase.
Eventually, this results in proportionally more H+ ions to remain in solution and increase acidity. Also, it means that ocean’s buffering capacity would decrease along with pH.