Increase In CO₂ Threatens Oceans

Carbon dioxide from burning fossil fuels is dramatically altering ocean chemistry and threatening marine life, according to a report released on July 5 by government and independent scientists. It warns that marine organisms that secrete skeletal structures, such as corals and pteropods (marine snails), may be profoundly affected by the rising acidification of surface ocean waters.

Between 1800 and 1994, the report says, the oceans absorbed 118 billion metric tons of CO₂ measured as carbon. Now they are absorbing 2 billion metric tons per year, about 30% of the CO₂ emitted to the atmosphere from the combustion of fossil fuel.

This added CO₂ has already increased the hydrogen ion concentration of the surface ocean by 30% and is predicted to increase it 150% relative to the preindustrial level by 2100. As the acidity rises, the availability of carbonate in the ocean decreases. By 2100, the calcification rates for coral and other creatures that build skeletons from calcium carbonate will decrease by up to 60%, the report says.

"It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life," says Joan Kleypas, the report's lead author and a scientist at the National Center for Atmospheric Research. "It is vital to develop research strategies to better understand the long-term vulnerabilities of sensitive marine organisms to these changes."

The ocean pH remained fairly stable for 650,000 years but recently has changed rapidly, says Richard A. Feely, one of the report's authors and an oceanographer at the National Oceanic & Atmospheric Administration (NOAA).

Many lab studies show that coral calcification decreases as the oceans become more acidic, threatening reef structures. "This threat is hitting coral reefs at the same time that they are being hit by warming-induced mass bleaching events"???the bleaching caused by warmer ocean temperatures, says Chris Langdon of the University of Miami.

Lab studies confirm that marine plankton, such as pteropods, are affected by declining concentrations of carbonate ion. Shelled pteropods are an important food source for salmon, mackerel, and cod. "Decreased calcification in marine algae and animals is likely to impact marine food webs and has the potential to substantially alter the productivity of the ocean," says Victoria J. Fabry of California State University, San Marcos.

The report is the outgrowth of a workshop funded by the National Science Foundation, NOAA, and the U.S. Geological Survey. It calls for a broad research strategy that should be pursued over the next five to 10 years to determine what effect the changes in ocean chemistry will have on marine life and ecology.