Antarctic Oceans Absorbing Less CO2, Experts Say

Kate Ravilious
for National Geographic News
May 17, 2007
The oceans surrounding Antarctica have lost some of their appetite for carbon dioxide, worrying scientists who are banking on the oceans to slow global warming, according to a new study.

They suspect stronger winds over these seas, which include parts of the Indian, Atlantic, and Pacific Oceans, are causing them to absorb less carbon dioxide, which is a greenhouse gas.

What's more, global warming and the ozone hole over the Southern Pole may be driving the fierce winds.

The oceans near Antarctica are thought to have one of the healthiest appetites for greenhouse gases.

Their surface waters can guzzle around 15 percent of all the carbon dioxide produced by people—which comes mostly from industry and automobile emissions.

The new study found the oceans are mopping up only about 10 percent of carbon dioxide—requiring projections for future levels of greenhouse gases to be bumped up accordingly.

Study lead author Corinne Le Quéré, of the Max Planck Institute for Biochemistry in Jena, Germany, and colleagues examined atmospheric carbon dioxide measurements taken from points around the world during the past 24 years.

The scientists calculated the rate of change of carbon dioxide concentrations at each of the measurement stations.

By doing so, the team was able to estimate where the main sources and "sinks"—spots such as oceans and forests that soak up large amounts of carbon dioxide—are, and how they have fluctuated over time.

(Related: "Oceans Found to Absorb Half of All Man-Made Carbon Dioxide" [July 15, 2004].)

A Modest Appetite

The researchers found carbon dioxide emissions have increased by 40 percent in the past few decades.

Le Quéré and colleagues had expected to see a corresponding increase in the levels of carbon dioxide mopped up by the oceans surrounding Antartica, but insted, they found it wasn't keeping pace.

"The carbon dioxide sink in the [oceans] remained completely flat," Le Quéré said.

Since the 1980s, the team estimated that the oceans carbon dioxide sink mechanism has weakened, and it is currently absorbing around one-third less than expected.

That means about 5 percent of human-caused greenhouse emissions are being left with nowhere to go.

Previous calculations have suggested that the oceans around Antarctica had capacity to absorb even more carbon dioxide, so the scientists were surprised to find the current low rate of uptake.

A Windy Predicament

Since 1958, there has been an increase in windiness over these oceans, according to a model produced by Le Quéré and colleagues.

The research, which will appear in tomorrow's issue in the journal Science, showed stronger gales cause more mixing of waters.

Deep, undisturbed ocean waters dissolve carbon dioxide more effectively. Surface waters have a higher concentration of carbon dioxide and cannot draw as much of it from the atmosphere.

The oceans near Antarctica are being churned up by the strong winds, hindering their ability to suck up carbon dioxide, the team concluded.

People to Blame

So what has made the winds blow?

It's likely an increase in greenhouse gases and less ozone, which have both changed how heat is distributed in the atmosphere, said Le Quéré.

These two phenomena work in concert to ramp up the wind shear, making the air whistle across the oceans faster than before.

Nicolas Gruber and Nicole Lovenduski, biochemists at the University of California, Los Angeles, recently carried out an independent study that backs up Le Quéré and colleagues' findings.

Gruber also developed a model that shows the carbon dioxide sink in the oceans near Antarctica has diminished since 1948. He presented his results in April at the European Geosciences Union General Assembly in Vienna, Austria.

A Vicious Cycle?

Gruber said he is concerned that the effect may get much worse.

"We could get into a positive feedback situation," he said.

For example, if the oceans absorb less carbon dioxide, then there is more of the gas in the atmosphere.

"This could make the wind strength increase even more, meaning the oceans absorb even less carbon dioxide, and so on," he said.

One small ray of hope is that the Southern ozone hole seems to be closing, which may help the winds to die down a little.

Nonetheless, the scientists say the public can't afford to be complacent.

"If the ocean is absorbing less carbon dioxide," said Gruber, "then we are going to have to work harder to reduce our emissions and stabilize greenhouse gases."

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