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Paper No. 269-5
Presentation Time: 9:00 AM-6:30 PM
SUBORBITAL-SCALE CO2 RECONSTRUCTIONS FROM THE EARLIEST MIOCENE BASED ON FOSSIL LEAVES
Determining the CO2 concentration of Earth’s atmosphere at different times in the past is important for understanding Earth’s climate sensitivity to this important greenhouse gas. Here we report estimates of atmospheric CO2 concentrations across a 100,000 year interval of the earliest Miocene (~23 million years ago), based on carbon isotopes (δ13C) and stomatal conductance measurements made on exquisitely preserved fossil leaves from the Foulden Maar Diatomite, a lacustrine sedimentary deposit located in central Otago, New Zealand. CO2 estimates previously developed from this archive were made using δ13C values of sedimentary leaf waxes and stomatal conductance values determined from fossil leaves, and indicated a large and transient CO2 rise associated with the termination of the Mi-1 Antarctic glaciation . We will present new CO2 estimates from the site, based on paired whole fossil leaf δ13C measurements and stomatal measurements made on the same fossil leaf specimens (n > 150). Leaves were identified to the family level and taxon-specific CO2 estimates across the 100,000 year interval were made based on different members of the ancient forest ecosystem. The results highlight the importance of the source and specificity of δ13C values and stomatal conductance measurements used for CO2 reconstructions based on stomatal gas diffusion models. This study represents the most comprehensive investigation to date of leaf-specific responses of different members of a forest ecosystem to environmental changes occurring at orbital and sub-orbital timescales.