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The latest on the Southern Ocean sink

At a conference this week, marine scientist Andrew Lenton of the Université Pierre et Marie Curie presented a new model that sketches out a beautiful causal chain: from the ozone hole over Antarctica, to rising southern winds, to stronger Southern Ocean currents, to more deep-sea stored carbon arriving at the sea surface.

The simulation, which Lenton reported at a meeting of the CARBOOCEAN research consortium in Dourdan, France, is the first coupled carbon-climate model to account for what biogeochemists have recently seen in the Antarctic waters. As I noted last month, observations (Science, subscription required) suggest the Southern Ocean’s considerable carbon dioxide sink isn’t soaking up as much of the gas as climate modellers expected, perhaps because there’s already too much dissolved in surface waters. That means more climate-warming carbon accumulates in the atmosphere.

By bringing in stratospheric ozone damage, which earlier studies had excluded, the model of Lenton and his colleagues manages to reproduce the recent disappointing sink – a step toward resetting future projections.

I reported this story for Nature News this week, and it posed two problems. One, I didn’t get to go to France – I heard it all here at my desk. Two, an issue flagged up in my earlier post also dogs Lenton’s research. One of the links in the chain – between speedy winds and more powerful Southern Ocean circulation – isn’t supported by oceanographic data (Nature Geoscience, subscription required).

This contradiction left Corrine Le Quere, the University of East Anglia marine scientist who led the research revealing saturation of the Southern Ocean sink, at a bit of a loss. “We see [the saturation] in the data,” she says; but “I don’t have very much confidence in the explanation of the process.”

Lenton thinks more detailed modelling might show that other mechanisms besides the questionable current bring carbon to the Southern Ocean surface. For more details, read the story here.

Anna Barnett


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