Sea Change: Carbon Dioxide Imperils Marine Ecosystems

Article excerpt

Almost half the carbon dioxide produced by human activity in the past 2 centuries is now dissolved in the oceans. It's wreaking chemical changes there that, if unchecked, could threaten the capacity of corals and other marine organisms to make their hard shells and skeletons, scientists say.

From 1800 to 1994, fossil fuel use and industrial processes such as cement production generated some 900 billion metric tons of carbon dioxide. Atmospheric concentrations of the planet-warming greenhouse gas rose during that period from about 280 parts per million to around 360 ppm, says Christopher L. Sabine, an oceanographer at the National Oceanic and Atmospheric Administration (NOAA) in Seattle. He reports that data garnered during more than 95 recent transoceanic research cruises suggest that much carbon dioxide ended up in the oceans as well.

Between 1989 and 1998, seagoing researchers measured the oceans' temperature, pH, salinity, and other aspects of marine chemistry from the water's surface to the seafloor. In a report in the July 16 Science, Sabine and his colleagues estimate that between 1800 and 1994, the world's oceans absorbed about 433 billion metric tons of industrial carbon dioxide.

The threat to shell-making marine life follows from the carbonic acid ([H.sub.2]C[O.sub.3]) that forms when carbon dioxide dissolves in water. In the ocean, much of that acid reacts with carbonate ions in the water to form nonacidic compounds (SN: 8/17/02, p. 104).

Carbonate ions are abundant in most surface waters, and corals and some free-swimming organisms use the material to form their calcium carbonate skeletons or shells, says Richard A. Feely, a marine chemist also at NOAA in Seattle. As ocean chemistry has slowly changed over the past 2 centuries, however, there's been a decrease in the range of depths at which the two most common forms of biomineralized calcium carbonate--aragonite and calcite--can dissolve. …