Recent studies show that the steady increase in atmospheric CO 2 parallels observed increase in air and sea surface temperature over the past 10 years. In order to assess changes in climate over time, a detailed record of both past and present climate conditions is needed. Historical instrumental data extend only as far back as 100 years, at best. Recent research, however, indicates that the stable isotopic record in scleractinian coral skeletal can be used to reconstruct high resolution paleoclimatic records from tropical latitudes. Corals can live for several hundred years, depositing a calcium carbonate skeleton in distinct bands that reflect the isotopic composition of the surrounding environment.
Fractionation refers to the kenetics of isotopes.
The lighter 12 C is preferentially used in metabolic processes. As a result, the relative proportions of heavy and light carbon in the coral skeleton depend upon the physical properties of the surrounding seawater and physiological processes in the coral animal. In symbiotic corals photosynthetically-derived carbon contributes up to 90 percent of carbon pool. Since photosynthesis is dependent on light, and carbon is metabolically fractionated in corals, variation in light levels should be reflected in the coral skeleton d 13 C signature. Results were significantly different from controls at both depths with the exception of the combined reduced light and zooplankton treatment at 7m.