Question

Explain the process of buffering that occurs in oceans.

Answer 1

bicarbonate can act as an acid or a base (i.e., donate or accept hydrogen ions) depending on conditions.

Under present-day conditions, these reactions buffer the pH of surface seawater at a slightly basic value of about 8.1 (above the neutral value around 7.0). At this pH, the total dissolved inorganic carbon (DIC ~ 2 mM) consists of approximately 1% CO2, 90% HCO3–, and 9% CO32– (Figure 2.1). The total boric acid concentration (B(OH)4– + B(OH)3)) is about 1/5 that of DIC. As discussed in section 2.2, increases in CO2 will increase the H+concentration, thus decreasing pH; the opposite occurs when CO2 decreases. We note that isotope fractionation between B(OH)3 and B(OH)4–is used for estimating past pH values

Answer 2

In simple chemical terms it plays out as follows:
When CO2 dissolves in seawater it combines with water to form hydrogen (H+) and bicarbonate (HCO3-) ions: 
CO2 + H2O -> H(+) + HCO3(-)
Some of the hydrogen ions combine with carbonate (CO3(2-)) ions to form additional bicarbonate ions resulting in a decrease in the former and an increase in the latter:
H(+) + CO3(2-) -> HCO3(-)
Therefore, the net effect when is added to seawater is for the concentrations of H+, CO2, and HCO3- to increase, and the concentration of CO32- to decrease.