July 15 (Bloomberg) -- Almost half the carbon emitted by the use of fossil fuel during the past 200 years has entered the world's oceans, threatening coral and shell-forming organisms, a study in the July 16 edition of the journal Science found.

The amount of carbon in the atmosphere has increased 36 percent in the last two centuries, the study said. During that time, oceans absorbed 119 billion metric tons of carbon dioxide, about one-third of its long-term potential.

The ocean has become a ``sink'' for carbon dioxide from fossil fuels such as coal and oil and from cement manufacturing, the study said. By absorbing the so-called greenhouse gas from the atmosphere, the oceans have blunted global warming, though the resulting increase in acid levels in the water puts marine animals at risk, the study said.

``The oceans provide a tremendous service to humankind,'' Christopher Sabine, an oceanographer at the National Oceanic and Atmospheric Administration, said in an interview from Washington.

The study warned that if fossil fuels are burned at projected rates, ocean organisms will have an increasingly difficult time forming their shells as the water becomes more acidic. Most of the research on carbon's effect on marine life has been conducted in a laboratory, and further study is needed, Sabine said.

The 10-year study of the Atlantic, Pacific and Indian oceans, sponsored by NOAA, the National Science Foundation and the U.S. Department of Energy, is the first global survey of the oceans since the 1970s. The study said it used 10 times the observations and is 10 times as accurate as the earlier research, the scientists said.

To contact the reporter on this story: Timothy W. Doyle in Washington at at tdoyle8@bloomberg.net.

Last Updated: July 15, 2004 14:07 EDT