Alkalinity and dissolution of calcium carbonate particles in the ocean

　Here, the conditional equation for the dissolution of calcium carbonate particles in seawater is written out.

The supersaturated state is, 【Ca²⁺】×【CO₃^2-】/ K_sp  >  1

The saturated (equilibrium) state is, 【Ca²⁺】×【CO₃^2-】/ K_sp  =  1

Undersaturated state is, 【Ca²⁺】×【CO₃^2-】/ K_sp  <  1.

　Since Ca²⁺ ions in seawater are abundant, 【Ca²⁺】 can be considered unchanged. Therefore, as 【CO₃^2-】 in seawater becomes smaller, it becomes undersaturated with respect to calcium carbonate and CaCO₃ particles dissolve.

Conditions for small 【CO₃^2-】 in seawater　

　So what are the conditions under which 【CO₃^2-】 in seawater becomes smaller? As we have already learned, as the pH of seawater decreases, the dissociation equilibrium of carbonic acid substances shifts, and the ratio of CO₃^2- to DIC becomes smaller: at pH 8, CO₃^2-/DIC = 9%, but at pH 7, CO₃^2-/DIC = less than 1%.