Carbon Isotope and Stomatal Data of Late Pliocene Betulaceae Leaves from SW China: Implications for Palaeoatmospheric CO2-levels


Abstract: The cuticular \delta^1^3C values and stomatal parameters (stomatal density and stomatal index: SD and SI) of two Betulaceae species, Betula mioluminifera Hu et Chaney and Carpinus miofangiana Nathorst, from a suite of superposed horizons in West Yunnan, southwestern China, were measured in order to recover Late Pliocene CO2 levels. Correlations are given for \delta^1^3C, SD, epidermal cell density (ECD), and SI. \delta^1^3C reveals a positive trend with the SD and SI in the two species, and such a positive correlation can also be observed between the \delta^1^3C and ECD in C. miofangiana. However, \delta^1^3C has a slightly negative correlation with the ECD in B. mioluminifera (R2= 0.06), possibly influenced by their different genotypes. Reflecting the changes through time, the \delta^1^3C values of B. mioluminifera and C. miofangiana significantly increase with high determination coefficients (R2= 0.67 and R2= 0.65, respectively), as do SD (R2= 0.66 and R2= 0.51, respectively) and SI (R2= 0.50 and R2= 0.79, respectively). Research on extant B. luminifera and C. fangiana shows that the SD and especially SI, exhibit a prominent negative correlation with CO_2 concentration. Pliocene CO_2 levels are reconstructed as 381.5-439.4 ppmv and 377.8-472.3 ppmv, respectively, based on comparisons of the two fossil species with their nearest living equivalent (NLE) species. The significant positive trends of the \delta^1^3C, SD and SI with ascending position of the fossils in the section indicate that the atmospheric CO_2 levels declined in the Late Pliocene (3.30-2.83 Ma). Furthermore, the calculated CO_2 levels are higher than in other studies and probably demonstrate that local CO_2 enrichment can be caused by frequent volcanic eruptions over a long time scale

Keywords: \delta^1^3C value, Betulaceae, stomatal parameters, atmospheric CO_2 concentration, Late Pliocene, Southwest China

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