Carbon Isotope and Stomatal Data of Late Pliocene Betulaceae Leaves from SW China: Implications for Palaeoatmospheric CO2 -levels
by Sun B.-N., Ding S.-T., Wu J.-Y., Dong C., Xie S., Lin Z.-C. ( 2012)
BAI-NIAN SUN 1 , SU-TING DING 1 , JING-YU WU 2 , CHONG DONG 3 , SANPING XIE 3 & ZHI-CHENG LIN 3
1 Lanzhou University, College of Earth and Environmental Sciences, Key Laboratory of Western China’s Environmental Systems of the Ministry of Education, Lanzhou 730000, China; State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing 210008, China
2 Lanzhou University, College of Earth and Environmental Sciences, Lanzhou 730000, China; State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing 210008, China
3 Lanzhou University, College of Earth and Environmental Sciences, Lanzhou 730000, China
in Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), 21: 237–250 – doi:10.3906/yer-1003-42 –
The cuticular δ13C 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 δ13C, SD, epidermal cell density (ECD), and SI. δ13C reveals a positive trend with the SD and SI in the two species, and such a positive correlation can also be observed between the δ13C and ECD in C. miofangiana. However, δ13C 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 δ13C 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 CO2 concentration. Pliocene CO2 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 δ13C, SD and SI with ascending position of the fossils in the section indicate that the atmospheric CO2 levels declined in the Late Pliocene (3.30–2.83 Ma). Furthermore, the calculated CO2 levels are higher than in other studies and probably demonstrate that local CO2 enrichment can be caused by frequent volcanic eruptions over a long time scale.