Today's average ocean pH has dropped from 8.2 to about 8.1 as the ocean has taken up a large amount of CO2 from human activities since the industrial revolution. Many students are confused by the change in carbonate ion concentration in the ocean resulting from the increase in oceanic CO2 uptake. This model provides students with an established oceanic carbon system. Students may uncouple the three reactions involving the changes in three inorganic carbon species and recognize the long-term system dynamic to develop a deep understanding of these changes.