Southern Ocean Sinks Carbon

Observations show that the Southern Ocean is still pulling CO₂ from the sky, but that may not last forever

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The oceans near Antarctica that absorb carbon and protect our planet from climate change have been working robustly in the past decade, finds a new study published yesterday in .

The study contradicts earlier inferences that the Southern Ocean’s carbon sink has been weak in the 21st century. The earlier studies were based on modeling, while the new study is based on observations.

The Southern Ocean encircles Antarctica and is home to a unique upwelling current that cycles carbon between the atmosphere and deep water. The upwelling is linked to the thermohaline circulation, which carries heat from pole to pole, and it is responsible for 40 percent of the total carbon that the global oceans take up.

Over the past decade, the capacity of the Southern Ocean to trap carbon has more than doubled, said Nicolas Gruber, a biogeochemist with the Eidgenössische Technische Hochschule, Zurich, and a co-author of the study.

If one were to assume that a ton of carbon is priced at $10, the Southern Ocean would be trapping more than $10 billion worth of carbon every year, he said.

“It is a significant ecosystem service that this ocean is doing,” he said.

This is not to say the sink will continue strengthening into the future. Carbon emissions have grown rapidly in the past decades, and humans emit about 10 petagrams of carbon per year. Only half of that enters the atmosphere, and the rest is absorbed by the land and oceans. The global oceans trap about a quarter (2.3 petagrams).

A weakening sink?

But wind systems may shift in the future and possibly reverse the sink, Gruber said.

“I would not say we should be relaxed,” he said.

The scientists used 2.6 million observations captured over 30 years to figure out the sink strength in the past.

Even more observations would be needed to simulate changes to the sink in the future, Sara Mikaloff-Fletcher, from the National Institute of Water and Atmospheric Research in New Zealand, wrote in an accompanying commentary.

“Although these studies represent an intriguing new picture of the Southern Ocean sink in the recent past, it is not yet clear how this region will respond to future changes in climate,” she wrote.

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