The thinning of the earth's UV umbrella (the hole in the ozone) over Antarctica has sparked fears that it may be impairing the Southern Ocean's ability to absorb carbon dioxide (CO2) from Earth's atmosphere.
Earth's oceans are the largest sink of carbon dioxide, with the Southern Ocean accounting for more than 40 percent of the annual uptake of the greenhouse gas, Andrew Lenton, a marine biochemist at the Pierre and Marie Curie University in Paris, told Nature News.
AdvertisementIn theory, seas should soak up more carbon dioxide as levels of the gas in the atmosphere rise.
But, recent measurements have showed that the Southern Ocean's surface waters have higher carbon levels than expected, which also makes them more acidic. As a result, the amount of CO2 that the ocean absorbs each year has also flattened out.
What was missing from the models, according to Lenton, was stratospheric ozone damage - which, along with the climatic effects of greenhouse-gas emissions, is thought to be behind the observed strengthening of southern winds.
According to Lenton, these winds may be causing ocean currents that stir up carbon stored in the deep ocean and bring it up to the surface.
Lenton and his colleagues built Southern Ocean simulations that coupled the ozone's effects on winds to ocean currents and marine carbon levels.
By running the models both with and without ozone depletion since 1975, the researchers "isolated the signal from ozone depletion", said Lenton's co-worker Francis Codron, an atmospheric scientist at the Dynamic Meteorology Laboratory in Paris.
Including the ozone hole reproduced the carbon sink that has observed by oceanographers.
"These sound like very different parts of the system, and yet one affects the other," said Codron.
The signal from ozone, the researchers found, drove a drop in Southern Ocean surface pH of 0.01 units from 1994 to 2004 - half the total pH decline in that period, and one-tenth of the change since the pre-industrial era.
Although the Antarctic ozone hole has stabilized in recent years and is expected to heal in the latter half of this century, climate models that don't include its effects may show an overly optimistic future, said Lenton.
According to Julie Arblaster of the Bureau of Meteorology Research Centre in Melbourne, Australia, "Understanding recent trends in the Southern Ocean carbon sink is key to understanding future projections of atmospheric CO2."
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