Interpreting environmental and biological signals from the stable carbon isotope composition of fossilized organic and inorganic carbon

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Abstract
Stable carbon isotope studies on marine and terrestrial organic and inorganic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric CO 2 . Comparison between the CO 2 estimates reconstructed from carbon isotope studies for the past 150Ma show good agreement with the predictions of a long-term carbon-cycle model based on mass-balance studies. Further, the CO 2 estimates from these sources over the entire Phanerozoic show agreement with the fossil record of leaf stomatal density change—a feature inversely related to the concentration of atmospheric CO 2 . Isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the C 4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species. The long-term perspective offered by these studies provides critical information for assessing the responses of biological systems to future global environmental change.