Acid Buildup in Oceans Threatens Food Chain

Robert Roy Britt

Date: 30 June 2005 Time: 07:55 AM ET

Sponge, coral, and searod on a reef off the Florida coast. Image: NOAA/Florida Keys National Marine Sanctuary
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Industrial and auto pollution could turn Earth's oceans so acidic by the end of this century that the entire marine world will be threatened, a new report warns.

The study, issued today by the Royal Society in the U.K., documents the rise of carbon dioxide, or C02, which occurs naturally and is also emitted in the burning of fossil fuels like coal and gasoline.

"If CO2 from human activities continues to rise, the oceans will become so acidic by 2100 it could threaten marine life in ways we can't anticipate," said Ken Caldeira, co-author of the report.

"This report should sound the alarm bells around the world," said Chris Field, director of the Carnegie Department of Global Ecology. "It provides compelling evidence for the need for a thorough understanding of the implications of ocean acidification. It also strengthens the case for rapid progress on reducing CO2 emissions."

Caldeira is a staff scientist at the Carnegie Institution's Department of Global Ecology in Stanford, Calif. He did the research while at the federal government's Lawrence Livermore National Laboratory.

Marine plants soak up carbon dioxide and convert it to food during photosynthesis. The CO2 is also used to make skeletons and shells, which ultimately become sediment on the sea floor. In that way, the oceans act as a giant carbon sink.

Some scientists estimate that more than a third of all human-produced C02 has been absorbed by the oceans.

What could happen

Caldeira and his colleagues conclude that too much C02 in the sea could have adverse effects. When CO2 gas dissolves into the ocean it produces carbonic acid, which corrodes shells of marine organisms and can interfere with their ability to take in oxygen. If current pollution trends continue, increasingly acidic water could hamper shell and coral formation and negatively impact the lives of crucial organisms such as phytoplankton and zooplankton that form the bottom of the food chain, the scientists say.

Any significant die-off of small creatures would have a deadly ripple effect throughout the watery ecosystem.

But Caldeira is careful to point out that nobody knows how all this might play out.

"We can predict the magnitude of the acidification based on the evidence that has been collected from the ocean's surface, the geological and historical record, ocean circulation models, and what's known about ocean chemistry," Caldeira said. "What we can't predict is just what acidic oceans mean to ocean ecology and to Earth's climate. International and governmental bodies must focus on this area before it's too late."

Anyone with a swimming pool or hot tub is familiar with the terms involved.

Acidity is measured on a scale of pH (potential of Hydrogen). It runs from 1 to 14, with 7 being neutral. Anything that lowers pH makes the solution more acidic. Over the past 200 years, the pH of the surface seawater has declined by 0.1 units, which is a 30 percent increase in hydrogen ions, Caldeira's team determined.

Creating Ice Age effects

The decline is about what occurred as the last Ice Age ended.

"Humans have already had as big a chemical impact on the oceans as going from the ice ages to today," Caldeira told LiveScience. "That change from the ice ages occurred over thousands of years, whereas most of the changes we have produced have come over the last century."

This buildup of hydrogen ions comes with a reduction in carbonate ions, which are the building blocks of calcium carbonate that corals and other organisms use to grow skeletons, according to a separate report last year issued by the The Pew Center on Global Climate Change.

The Pew report, led by Joan Kleypas of the National Center for Atmospheric Research (NCAR), reached a similar conclusion. Kleypas also said that corals are being damaged by increases in water temperature at the surface, a side effect of the controversial global warming that most scientists say is being exacerbated by industrial emissions.

"Coral reef ecosystems are going to be significantly impacted by climate change," Kleypas says. "They're already being degraded by both climate change and by direct impacts such as overfishing and habitat loss, and the combination of these stresses can be devastating."

Another study in December found that as up to 20 percent world's coral reefs have been destroyed, largely by warmer water and increases carbon dioxide. Reefs serve as homes for other marine life and protect shorelines against erosion.

Kick 'em when they're down

Further, a report yesterday said the sea is becoming less salty due to extra fresh water flowing in as a result of a warmer climate.

Caldeira said this won't have much effect on pH, but it is "further evidence that continued CO2 emissions may be damaging the marine environment in several ways," he said. "Not only are marine organisms having to cope with an increasingly acidic ocean, but they must also deal with decreasing saltiness and possible slowing of the large-scale circulation of the ocean."

If emissions of CO2 continue to rise as predicted in one scenario by the Intergovernmental Panel on Climate Change, there will be another drop in pH by .5 units by 2100, a level that has not existed in the oceans for many millions of years, Caldeira's team says.

The results were reached by measuring historic atmospheric C02 from ice cores, Caldeira explained, and through lab experiments and chemical calculations. The findings match the predictions of separate computer models, he said.