Carbon Dioxide's Effects on the Oceans Described by Science Researchers

As our vehicles, power plants and factories pump carbon dioxide into the atmosphere, nearly half of it enters the oceans, according to new findings in the 16 July 2004 issue of the journal Science. If this trend continues, it may harm some corals and shell-forming organisms, the researchers report.

The concentration of carbon dioxide in the atmosphere has been rising over the last two centuries. But only half of what's being released by fossil fuel burning and other human activities is actually staying in the atmosphere. For decades, researchers have been trying to find out what happens to the other half.

The oceans soak up major quantities of atmospheric carbon dioxide, but efforts to estimate exactly how much have been plagued by a large degree of uncertainty. More precise, reliable estimates will give researchers firmer footing as they study the implications of fossil fuel burning on global climate.

In order to get a better handle on the problem, two international ocean research programs collaborated on a survey of inorganic carbon distributions in the global oceans in the 1990s. Using these data, Science authors Richard Feely and Christopher Sabine of NOAA's Pacific Marine Environmental Laboratory have determined that the oceans absorbed 48 percent of the carbon dioxide emissions from fossil fuel burning and cement manufacturing between 1800 and 1994.

They estimated that the oceans took up approximately 118 billion metric tons of carbon dioxide during this period.

"For comparison, a small car weighs about one metric ton," Sabine said.

Feely and Sabine, along with Science editor Jesse Smith, discussed the research in a joint Science and NOAA news conference at AAAS on Thursday.

Although the oceans are effective at taking up carbon dioxide, "there is a price to pay," Feely said.

The increased carbon dioxide concentrations in the oceans have influenced ocean chemistry in a way that should make it difficult for some marine animals to form their shells, he explained.

Corals, pteropod mollusks and single-celled creatures called foraminifera and coccolithophorids pull carbonate ions from the seawater to produce their calcium carbonate shells. But, as the carbon dioxide concentrations increase in seawater, the carbonate ion concentrations decrease.

At depths where carbonate ion concentrations drop below a certain level, the calcium carbonate shells start to dissolve. Feely and Sabine estimated global calcium carbonate dissolution rates and predicted that if carbon dioxide emissions continue to increase, ocean areas where shell dissolution occurs should expand. This trend would likely begin with colder, high-latitude surface waters and proceed toward the equator.

The data gathered for the collaborative ocean survey had over 10 times the number of observations with ten times better accuracy than the last global survey, done in the 1970s, according to Sabine.

—Kathy Wren

16 July 2004