Biosphere 2 studies reflect real world changes

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BIOSPHERE 2 STUDIES REFLECT REAL WORLD CHANGES UniSci Science News University Science 19-Apr-1999 Levels of carbon dioxide, a greenhouse gas found in the earth's atmosphere, have increased since pre-industrialized times, primarily due to the combustion of fossil fuels. Scientific studies have suggested this trend will continue, resulting in a projected doubling of atmospheric carbon dioxide levels from preindustrial levels by the year 2065. This projected atmospheric change brings with it other potential and uncertain changes to the earth's atmosphere, biosphere and hydrosphere. Data collected from large-scale ocean surveys, for example, have indicated that surface waters of temperate and tropical oceans are taking up carbon dioxide in proportion to the earth's atmosphere.

Inside Columbia University's Biosphere 2 Center in Oracle, Ariz., Lamont-Doherty Earth Observatory Associate Research Scientist Chris Langdon directly tested and assessed the impact of elevated atmospheric carbon dioxide on coral reef building and maintenance. The ocean biome, one of six ecosystems located inside the Biosphere 2 Center, provided an ideal site to study these effects. Langdon's findings contributed, along with research conducted by other scientists, to a paper recently published in the journal Science , titled, "Geochemical consequences of increased atmospheric CO2 on coral reefs." The paper suggests that atmospheric changes in carbon dioxide levels could lead logically to negative changes in reef structure, coral reproduction, and overall function of

coral reef communities. "Chris' work at Biosphere 2 was invaluable to our analysis," said Joan A. Kleypas, a researcher at the National Center for Atmospheric Research in Boulder, Colo., who was the paper's primary author. "When we put this paper together, his results were the only 'ecosystem' results available. I think [the ocean biome at Biosphere 2] is presently the best available system for studies of reef response to ocean chemistry changes." Coral reefs serve many important functions, explains Langdon, as barriers protecting low-lying islands from erosion, habitats for diverse ecosystems, and aesthetically attractive areas that support a large tourism industry. A reef forms when corals and other marine organisms produce calcium carbonate, the solid

substance found in limestone, bones and sea shells, primarily as the mineral aragonite. In temperate and tropical shallow ocean areas with dense coral populations, this aragonite can accumulate to form reefs. For a reef community to build and maintain itself, the rate at which organisms deposit calcium carbonate must exceed the combined rates of physical, biological and chemical erosion of the reef. The reef-building process can be influenced by the level of carbon dioxide in the water, through a chemical process that weakens bonds of the calcium carbonate molecules that form reefs. Currently, surface ocean water is predominantly supersaturated with calcium carbonate, but the research reported in Science suggests the saturation state will decrease as atmospheric carbon dioxide

levels increase. This lowered saturation state can result in decreased rates of calcification, the process by which many coral species build reefs. In addition to its negative effects on reef building rates, a decreased saturation state may also reduce the strength of a reef's cementation processes, resulting in a weaker structure more susceptible to erosion. Langdon likens this structural weakening to osteoporosis, and explains that rising sea levels, which may result as increased temperatures caused by increased atmospheric carbon dioxide levels melt the polar ice caps, can further enhance erosion processes. To help draw a clear picture of the potential effects of atmospheric carbon dioxide levels on coral reef building and maintenance, Langdon raised the carbon dioxide level