The oceans are a very important carbon sink, as they absorb more carbon dioxide than they produce. This is due to the way in which gases naturally dissolve in seawater. As well, when waves break on the shore, atmospheric gases are introduced into the ocean. In addition to this, many marine organisms actively remove dissolved carbon dioxide (CO2) and calcium carbonate (CaCO3) from the water and incorporate these carbon species into their cellular and skeletal structures.
The Great Ocean Conveyor Belt circulates vast quantities of water all around the globe and transfers water that contains gigatonnes of carbon from surface layers down to greater depths, mixing water from different parts of the ocean. When carbon dioxide dissolves in water, it undergoes several equilibrium reactions. This shifts the speciation of carbon in the ocean, bringing more carbon dioxide into the water. As a result of these processes, more CO2 is dissolved in ocean water than would be possible otherwise. Nearly 40,000 Gt of carbon are stored in the ocean reservoir, whereas the atmosphere holds around 750 Gt carbon.