Scientists from Lawrence Livermore National Laboratory (LLNL) used computer models to discover that the Southern Ocean absorbs about one-third of all man-made carbon dioxide, because the greenhouse gas dissolves easily in cold water. But, the scientists warn, increased precipitation would warm the surface of the oicean, preventing the entrance of carbon dioxide into the ocean and increasing the rate of warming.

After discovering the Southern Ocean’s ability to absorb carbon dioxide, the researchers tested the ocean’s carbon dioxide levels, but found far less of the greenhouse gas than they expected.. Thinking that some of the early model results were inaccurate, they added the fact that the water in the ocean is divided into layers at different temperatures to their model.

Using their revised model, Caldeira and Duffy found that the carbon dioxide that gets absorbed by the Southern Ocean actually sinks into the deep subtropical ocean as it slides along the base of a layer of cold, dense water .

“Warm water sits on the top with colder, dense water below,” says Kenneth Caldeira, a climate scientist at LLNL. “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 absorbs atmospheric carbon dioxide.”

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.

“The fear is that if you warm things up too much, more precipitation will make the surface of the Southern Ocean less dense,” says Caldeira. “You may start shutting off the entrance of carbon dioxide into the ocean, and things would warm up a lot faster,” he says. But Caldeira concedes that studies also show that if things warm up, more microscopic plants that use carbon dioxide could compensate for a Southern Ocean shutdown.

Although there is plenty of room in the deep tropical ocean to store carbon dioxide, the ocean may not take up as much of the greenhouse gas in the future, says Caldeira. As the ocean absorbs more and more carbon dioxide, it becomes less able to absorb additional carbon dioxide because the water becomes acidic, so oceans may become less efficient at carbon uptake.

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