How does rising atmospheric CO2 affect marine organisms?

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Effects of CO2 on a Tropical Rainforest Mesocosm
Lin, G., Marino, B.D.V., Wei, Y., Adams, J., Tubiello, F. and Berry, J.A.  1998.  An experimental and modeling study of responses in ecosystems carbon exchanges to increasing CO2 concentrations using a tropical rainforest mesocosm.  Australian Journal of Plant Physiology 25: 547-556.

What was done
The authors measured the ecosystem carbon exchange rate of a 1700-m2 synthetic rainforest mesocosm at atmospheric CO2 concentrations of approximately 430 and 740 ppm.  This enormous study site, currently managed by Columbia University, is located within the 1.25-ha naturally-lit Biosphere 2 research "dome," which contains several large synthetic ecosystems enclosed by stainless steel sheets and glass.  After the dome's air was stabilized at a treatment CO2 level for about one week, the rainforest mesocosm was isolated from the rest of the dome for one to three days so its carbon exchange rate could be measured.

What was learned
A 72% increase in atmospheric CO2 concentration increased the daytime net ecosystem carbon exchange rate of the synthetic rainforest by 79%, without affecting the amount of carbon respired from the soil.  This observation indicates that elevated CO2 enhanced ecosystem carbon uptake mainly by increasing canopy net photosynthesis, as atmospheric CO2 enrichment had no significant effect on soil respiration.

What it means
As the CO2 content of the air continues to rise, tropical rainforests will likely increase their photosynthetic capacity.  This phenomenon may apply a significant "biological brake" on the rising CO2 content of the atmosphere, as tropical rainforests are among the most productive ecosystems on earth, and a large stimulation of their photosynthetic capacity should result in the removal of tremendous amounts of carbon from the atmosphere.

Reviewed 15 October 1998