Fossil leaves: Effective bioindicators of ancient CO 2 levels?

[1] Past variations in the concentration of the greenhouse gas CO2 are thought to have played a major role in controlling Earth’s climate on preQuaternary and Quaternary timescales. To identify the contribution of CO2 to past climatic change requires accurate quantification of its content in the ancient atmosphere, and a number of proxies have been developed for this purpose (for a review see Royer et al. [2001a]). For the Late Quaternary, there is the unique opportunity to measure directly the composition of fossil air samples trapped in bubbles preserved in the polar ice sheets. Results from Antarctic ice cores reveal that the glacialinterglacial changes characterizing Quaternary climate were accompanied by variations in the atmospheric concentration of CO2 [Petit et al., 1999]. Although detection of phase relations between isotope-derived temperature estimates and trace gas concentration values is hampered by the difference in age of ice and air from the same ice sample, it is believed that CO2 lags glacial-interglacial temperature change and has acted as an amplifier of orbitally forced changes in temperature [Petit et al., 1999; Shackleton, 2000; Mudelsee, 2001].