Different science overview
There are some good data presentations here:
http://www.appinsys.com/globalwarming/OceanAcidification.htm
A student definition???
Definition: Acidic: containing or having the properties of an acid, “Pertaining to substances that have a pH lower than 7” [http://www.biology-online.org/dictionary/Acidic]. While the term acidification refers to decreasing pH, the term acidic is only valid when the pH is less than 7.
The concern is that as the atmospheric CO2 increases, it increases the CO2 content of the ocean, resulting in increased carbonic acid (H2CO3). The following equation shows the basic equilibrium equation involved in the water (with <=> denoting equilibrium):
CO2 + H2O <=> H2CO3 <=> H+ + HCO3-