Carbon dioxide hampers ability of bottom of
food chain to thrive, federal report finds
- David Perlman, Chronicle Science Editor
Thursday, July 6, 2006
The major greenhouse gas that drives global warming also is rapidly raising the acidity of the world's oceans, threatening widespread destruction of the tiny shell-building organisms that form the base of the entire marine food web and create corral reefs, a team of government-sponsored scientists said Wednesday.
The culprit is carbon dioxide. As billions of tons of the carbon in the
gas pour from industrial emissions into the ocean, it is causing "the
most dramatic changes in marine chemistry in the past 650,000 years,"
said Richard Feely, a federal oceanographer in Seattle and one of the
team's leaders.
The landmark report by the research group, sponsored by the National Science Foundation, the National Oceanic and Atmospheric Administration and the U.S. Geological Survey, was released Wednesday, and the findings are indisputable, said one lead scientist.
"Unlike any possible controversy over global warming, as you increase carbon dioxide in the atmosphere, you're driving carbon into the oceans and increasing the ocean's acidity -- and this is not debatable," said Joan Kleypas, an ecologist and geologist in Boulder, Colo.
The 88-page report resulted from a workshop held last year in Florida, where more than 50 marine scientists from nine nations gathered to pool their research results and reached consensus on the problem.
The scientists noted that carbon changes the ocean's chemical nature from normally alkaline to abnormally acidic. That change, in turn, lowers the concentration of carbonate ions, which are the building blocks of the calcium carbonate that many of the most important marine organisms use to grow their shells and create the structures that form coral reefs that provide vital habitat for fish and other marine species, the scientists explained.
The pace of change from alkaline to acidic water, the report said, has increased rapidly over the past 200 years as industrial carbon dioxide in the atmosphere dumped more carbon into the world's oceans. For hundreds of thousands of years before that, the acidity of the world's oceans remained steady based on the study of ice cores, the scientists said.
Between 1800 and 1994, the oceans worldwide absorbed more than 118 billion metric tons of carbon, according to Feely of the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory. By now, he said, that total has increased to 142 billion tons, with more than 2 billion tons entering the oceans every year.
"The rate of change in the ocean's chemistry now is truly extraordinary," said Kleypas of the National Center for Atmospheric Research, the senior author of the report.
Organisms that build their shells of calcium carbonate are known as marine calcifiers, and they include the microscopic plankton creatures called coccolithophores and the foraminifera -- or forams, as they're known -- that exist in the seas by the millions at the base of the marine food chain.
"They are a major food source supporting fish like salmon, mackerel and cod, and the shells of the calcifiers are highly susceptible to dissolving in the increasingly corrosive acid waters," said Victoria Fabry, a biological oceanographer at Cal State San Marcos. "We don't yet know how those organisms will adapt to the chemical change, but their populations are sure to decline by the end of the century, or even in the next 50 years."
After years of laboratory experiments and research cruises analyzing chemical changes in ocean waters from the tropics to the Arctic, the scientists are unanimous both in their report's conclusions that the marine calcifiers are in danger and in their knowledge that many details of the threat are still uncertain.
The effects of large-scale changes in ocean chemistry on marine ecology are poorly understood, but the changes themselves are clear, and marine life is bound to change dramatically within coming decades, the scientists agreed.
"This is a call to arms," said Christopher Sabine, an engineer with the National Oceanic and Atmospheric Administration in Seattle. "It's a major issue, and we need to make it a major international focus of research."
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