[djf]

I'm not sure, but I think most of the CO2 in the oceans isn't dissolved gasses, but is Calcium Carbonate. Clamshells, limestone, various diatoms.

[kabar]

CO2 is a gas. CACO3 is a solid. Most of the CO2 in sea water is in the form of bicarbonate HCO3. Some of the important atmospheric gases found in seawater include: nitrogen, oxygen, carbon dioxide (in the form of bicarbonate HCO3), argon, helium, and neon. Compared to the other atmospheric gases, the amount of carbon dioxide dissolved in saturated seawater is unusually large.

There is an exchange of carbon dioxide between the atmosphere and the ocean’s surface. Carbon dioxide dissolves in the ocean and provides the source of carbon dioxide that plants and plankton living in the ocean rely on for photosynthesis. The amount of carbon dioxide the ocean can contain depends on the temperature of the water and on its saltiness (whether it is sea water or fresh water). Cold water can hold more carbon dioxide in solution than warm water. When carbon dioxide dissolves in water, it forms carbonic acid which makes the water acidic. In the lab we can test for the acidity caused by the presence of dissolved carbon dioxide using Universal Indicator, which turns yellow when the solution is acidic. This activity tests whether sea water or fresh water absorbs more carbon dioxide. Sea water can absorb more carbon dioxide than fresh water without having major environmental effects.