Pollution is quickly making the world’s oceans more acidic, and if unchecked this could cause a mass extinction of marine life similar to one that occurred when the dinosaurs disappeared, a researcher says.

The researcher, Ken Caldeira of the Carnegie Institution of Washington, D.C., has developed computer models predicting a continuation of a trend other scientists have also noted: the oceans are slowly turning into mild acids.

Caldeira said he compared his computer models predicting how far this will go in the next century, with evidence from the fossil record, and has found some startling similarities.

The finding offers a glimpse of what the future might hold for ocean life if society does not drastically curb carbon dioxide emissions, he added.

“The geologic record tells us the chemical effects of ocean acidification would last tens of thousands of years,” Caldeira said. “But biological recovery could take millions of years. Ocean acidification has the potential to cause extinction of many marine species.”

When carbon dioxide from the burning of coal, oil, and gas dissolves in the ocean, some of it becomes carbonic acid. Over time, accumulation of this carbonic acid makes ocean water more acidic.

Previous estimates, Caldeira said, suggest that in less than a century, the pH of the oceans could drop by as much as half a unit from its natural value of 8.2 to about 7.7. On the pH scale, lower numbers are more acidic and higher numbers are more basic.

This trend would especially damage marine animals such as corals, that make shells out of a mineral called calcium carbonate, Caldeira added. Under normal conditions the ocean is full of this substance, making growth easy for such creatures. A more acidic ocean would more easily dissolve calcium carbonate, putting these species at severe risk, he added.

The last time the oceans endured such a drastic change in chemistry, he added, was 65 million years ago, when the dinosaurs went extinct.

Though researchers don’t yet know what caused this ancient acidification, it was related to the cataclysm that wiped out the giant beasts, he added. The extinction pattern in the ocean was consistent with ocean acidification, he explained: the fossil record reveals a plunge in the number of species with calcium carbonate shells in the upper ocean, especially corals and plankton.

During the same period, species with shells made from resistant silicate minerals were more likely to survive.

“Our energy system could make the oceans corrosive to coral reefs and many other marine organisms,” Caldeira cautioned. He presented the findings Monday in Honolulu at the Ocean Sciences Meeting of the American Geophysical Union and the American Society of Limnology and Oceanography.


- Courtesy the Carnegie Institution
and World Science staff

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