The organic matter may then be consumed by animals. Either plants or animals may respire the organic carbon to produce energy, consuming O 2 . This mismatch results in an excess of oxygen and a deficit of CO 2 in surface waters, and the reverse in deep waters. In some surface waters oxygen can be supersaturated. At the pH of seawater, most of the total CO 2 in the ocean is present as bicarbonate.
Carbon dioxide is the most abundant greenhouse gas, meaning that it traps infrared radiation.
The concentration of CO 2 in the atmosphere has been increasing for at least the last few decades, and there is concern that this may result in global warming because the radiation of heat from the earth's surface is reduced. However, the increase in atmospheric CO 2 is much less than expected from the amount of fossil fuel burned, and part of the difference may be that some of this CO 2 has gone into the ocean. Thus, there is intense interest in the biogeochemistry of CO 2 in the ocean. The oceanic CO 2 cycle is difficult to understand because significant processes occur in all the world's oceans and the variability in these processes makes accurate long-term averages difficult to obtain. At present we do not know if the ocean is a net consumer of excess CO 2 or not.