Now researchers have found that the carbon dioxide actually ends up deep in the subtropical ocean and will report their findings in the Jan. 28 issue of the journal Science. When scientists first started using computer models to see what happens to carbon dioxide added to the atmosphere by humans, the models showed that lots of the greenhouse gas was sponged up from the atmosphere and stored in the cold Southern Ocean, said Kenneth Caldeira, a climate scientist from Lawrence Livermore National Laboratory. But when scientists tested the water in the Southern Ocean, they didn't find the massive stockpile that would have accumulated if the ocean was storing man-made carbon dioxide. If the ocean didn't soak up carbon dioxide, the amount in the atmosphere would increase a lot faster. Caldeira and Philip Duffy, also from Lawrence Livermore, added factors to their computer model that made the global oceans more realistic.
Warm water sits on the top with colder, dense water below.
When the water is very cold, like it is in the Southern Ocean in wintertime, the cold layer of water is very close to the surface and it grabs carbon dioxide out of the atmosphere. There is a boundary dividing warm surface water and colder waters below. That boundary is very close to the surface in the Southern Ocean, but it becomes deeper and deeper as it runs north into the tropics, where the interface between warm and cold water is as much as a mile deep. Using their new model, Caldeira and Duffy found that the carbon dioxide that gets absorbed by the Southern Ocean actually ends up in the subtropical latitudes as it slides along base of the cold, dense water layer and sinks into the deep subtropical ocean. Some scientists expect that global warming will make the Southern Ocean less able to take carbon dioxide out of the air.