1999-10 BOULDER--Tropical coral reefs could be directly threatened by the buildup of atmospheric carbon dioxide (CO2) entering the oceans, and some reefs may already be declining, say six scientists in a paper published in the April 2 issue of the journal Science. Writes lead author Joan Kleypas of the National Center for Atmospheric Research (NCAR), "We believe that these findings represent some of the first evidence of a direct negative impact of increased CO2 on a marine ecosystem." NCAR's primary sponsor is the National Science Foundation.
The team's findings apply primarily to coral reefs located in surface waters between 35 degrees north and 35 degrees south of the equator. However, the authors predict that reefs in greatest danger are those where the production and destruction of calcium carbonate are closely balanced. These include some higher-latitude reefs, such as those off Bermuda; those in areas where colder, deeper waters rise to the surface, such as those off the Galapagos Islands; and many reefs already stressed by human activity.
A coral reef is the accumulation of calcium carbonate produced by the corals and other calcium-secreting organisms, such as coralline algae. If calcium production declines, coral and algal skeletons will weaken and reef building may slow or stop. The reef then becomes more vulnerable to erosion. Ongoing calcium production depends on the saturation state of calcium carbonate in surrounding surface waters. This saturation state declines as CO2 enters tropical surface waters.
Carbon dioxide is an important greenhouse gas produced by fossil-fuel
use. For their study, the authors used future scenarios in which the
preindustrial level of CO2 doubles by the year 2065--considered a
moderate projection by the Intergovernmental Panel on Climate Change, an
international group of 2,500 scientists. As the gas builds up in the
atmosphere, the tropical sea s
National Center for Atmospheric Research/University Corporation for Atmospheric Research