Ocean acidification worst for 300 million years

Posted by Emma Woollacott

The world's oceans appear to be acidifying faster than at any time in the last 300 million years, and sea life may well be unable to adapt.

The last time acidification took place anywhere near this fast was during the Paleocene-Eocene Thermal Maximum, or PETM.

In the last hundred years, rising carbon dioxide from human activities has lowered ocean pH by 0.1 unit, and the Intergovernmental Panel on Climate Change (IPCC) predicts that pH will fall another 0.2 units by 2100, raising the possibility that we may soon see the same sort of ocean changes as those observed during the PETM.


"We know that life during past ocean acidification events was not wiped out - new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about - coral reefs, oysters, salmon."

The oceans act like a sponge to draw down excess carbon dioxide from the air, which then reacts with seawater to form carbonic acid.


And in a review of hundreds of paleoceanographic studies, the researchers say, only the PETM is comparable.



As many as half of all species of benthic foraminifera, a group of one-celled organisms that live at the ocean bottom, went extinct, suggesting that deep-sea organisms higher on the food chain may have also disappeared, says Ellen Thomas, a paleoceanographer at Yale University.


Scientists estimate that ocean acidity may have fallen as much as 0.45 units as the planet vented stores of carbon into the air.

"The ocean acidification we're seeing today is unprecedented, even when viewed through the lens of the past 300 million years - a result of the very fast rates at which we're changing the chemistry of the atmosphere and oceans," says Candace Major, program officer in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research.