INTERPRETING ENVIRONMENTAL AND BIOLOGICAL SIGNALS FROM THE STABLE CARBON-ISOTOPE COMPOSITION OF FOSSILIZED ORGANIC AND INORGANIC CARBON

Stable carbon isotope studies on marine and terrestrial organic and in organic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric CO2. Comparison between the CO2 estimates reconstructed from carbon isotope studies f or the past 150 Ma 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 agreem ent with the fossil record of leaf stomatal density change-a feature i nversely related to the concentration of atmospheric CO2. Isotopic stu dies on temporal sequences of fossilized terrestrial organic matter ha ve contributed to palaeoecological studies on shifts in the dominance of plants with the C-4 photosynthetic pathway in ecosystems and histor ical changes in the metabolic processes of leaves of individual specie s. The long-term perspective offered by these studies provides critica l information for assessing the responses of biological systems to fut ure global environmental change.