Southern Ocean soaks up carbon dioxide

Manmade carbon dioxide in the ocean makes the water more acidic. The acidity is corrosive to calcium carbonate, an essential ingredient of shells and coral reefs.

January 28, 2000
Web posted at: 1:59 p.m. EST (1859 GMT)

By Environmental News Network staff

Manmade carbon dioxide is being soaked up by the cold waters of the Southern Ocean and transported to the deep waters of the subtropical ocean, researchers report in today's issue of Science.

The thirst-quencher, it turns out, might not be kind to the marine environment. Manmade carbon dioxide makes the water more acidic. The acidity is corrosive to calcium carbonate, an essential ingredient of shells and coral reefs.

The new research is helping scientists solve an old mystery. Early computer models show carbon dioxide being soaked up by the Southern, or Antarctic, Ocean even though water samples from the ocean do not show the presence of carbon.

"Early results suggested that a lot of carbon was going in (the ocean) at 60 degrees (south latitude), but when people went there, they didn't see any," said Ken Caldeira, a climate scientist at Lawrence Livermore National Laboratory in Livermore, California. "But they saw lots at 40 degrees."

How did the carbon get there?

Ocean water is layered, with warm water on top of cold, denser water, Caldeira explained. When a balloon filled with cold, dense water is lifted up to warmer, less dense water, it sinks back down. Push down on the balloon and it will float back up.

Caldeira refers to this phenomenon as a "restoring force." "If you move (the balloon) sideways, there is no restoring force," he said.

Carbon, like a balloon, can easily slide along a layer of constant density. This mechanism, technically referred to as "isopycnal transport," is how carbon moves from the Southern Ocean to deep subtropical ocean waters, according to Caldeira.

Carbon, like a balloon, can easily slide along a layer of constant density. This mechanism, technically referred to as "isopycnal transport," is how carbon moves from the Southern Ocean to deep subtropical ocean waters.

Since carbon dioxide easily dissolves in cold water, pockets of the chilly Southern Ocean soak it up. This layer of cold water moves deeper and deeper as it runs north into the tropics, explaining why the carbon is found so deep in the subtropical ocean.

Some scientists predict that the Southern Ocean's ability to drink up carbon dioxide may be hindered by global warming. "The fear is that if you warm things up too much, more precipitation will make the surface of the Southern Ocean less dense. You may start shutting off the entrance of carbon dioxide into the ocean," said Caldeira.

However, other studies show that if the world continues to warm, more microscopic plants that use carbon dioxide will blossom and compensate, he added.

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