ES&T - Ozone Loss Increasing Southern Ocean Acidification, Cutting CO2 Absorption

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ublication Date (Web): July 8, 2009

In addition to weakening Earth’s natural shield against excessive radiation levels, ozone depletion above Antarctica has significantly dampened the Southern Ocean’s ability to absorb atmospheric CO2 and has accelerated acidification of southern polar waters, according to new research reported online June 20 in Geophysical Research Letters (2009, DOI 10.1029/2009GL038227).

Of the atmospheric CO2 generated by humans and absorbed by the world’s oceans, more than 40% is believed to be taken up by the Southern Ocean; this makes that body of water one of the planet’s major carbon sinks. Global climate models have predicted that southern polar waters would compensate for the steadily rising CO2 levels by soaking up the greenhouse gas. However, recent studies based on shipboard measurements have revealed declining CO2 uptake in those waters. Scientists have posited that intensified westerly winds caused by the ozone hole drive surface water to mix with deeper, CO2-rich water, thus limiting the ocean’s capacity to draw the gas down from the atmosphere.

To calculate the changes in ocean–atmosphere carbon balances for the period 1975–2004, Andrew Lenton and colleagues at the National Center for Scientific Research (France) used a model that included the impacts of changing ozone concentrations. The researchers compared two scenarios: one that accounted for ozone depletion and another in which no ozone alterations occurred. The results revealed that, during the period examined, the Southern Ocean absorbed about 9 billion tons less CO2 in the ozone-depletion scenario than it would have with an intact ozone layer. Furthermore, about 50% of the observed 0.02 unit decline in seawater pH during the study period could be attributed to the addition of CO2 in the upper ocean as a result of the ozone-hole-induced upwelling, the researchers found.

“This is a good study, and it confirms recent field observations on changes in surface winds and ocean carbon,” says atmospheric scientist David Battisti of the University of Washington. “The results indicate that ozone depletion reduced oceanic CO2 uptake by roughly 10% over the 17-year period—not an insignificant change,” he notes.

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http://pubs.acs.org/action/showStoryContent?doi=10.1021/on.2009.07.07.396592&cookieSet=1