title: Reconstructing atmospheric CO2 during the Plio-Pleistocene transition by fossil Typha.
abstract: The Earth has undergone a significant climate switch from greenhouse to icehouse during the Plio-Pleistocene transition (PPT) around 2.7-2.4 million years ago (Ma), marked by the intensification of the Northern Hemisphere glaciation (NHG) ~2.7 Ma. Evidence based on oceanic CO2 [(CO2)aq], supposed to be in close equilibrium with the atmospheric CO2 [(CO2)atm], suggests that the CO2 decline might drive such climate cooling. However, the rarity of direct evidence from [CO2]atm during the interval prevents determination of the atmospheric CO2 level and further assessment on the impact of its fluctuation. Here, we reconstruct the [CO2]atm level during 2.77-2.52 Ma based on a new developed proxy of stomatal index on Typha orientalis leaves from Shanxi, North China, and depict the first [CO2]atm curve over the past 5 Ma by using stomata-based [CO2]atm data. Comparisons of the terrestrial-based [CO2]atm and the existed marine-based [CO2]aq curves show a similar general trend but with different intensity of fluctuations. Our data reveal that the high peak of [CO2]atm occurred at 2.77-2.52 Ma with a lower [CO2]aq background. The subsequent sharp fall in [CO2]atm level might be responsible for the intensification of the NHG based on their general temporal synchronism. These findings shed a significant light for our understanding toward the [CO2]atm changes and its ecological impact since 5 Ma.
authors.affiliation: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Yun-Jun
authors.initials: YJ
authors.lastname: Bai
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Chen
authors.forename: Parminder S
authors.initials: PS
authors.lastname: Ranhotra
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
authors.forename: Yu-Fei
authors.initials: YF
authors.lastname: Wang
authors.forename: Cheng-Sen
authors.initials: CS
authors.lastname: Li
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002245:Carbon Dioxide / Q000032:analysis*; D002681:China; D057231:Climate Change; D005580:Fossils; D054046:Plant Stomata / Q000737:chemistry; D032401:Typhaceae / Q000737:chemistry*
chemical_list: D002245:Carbon Dioxide
keywords: North China; Northern Hemisphere glaciation; Paleo-CO2; Plio-Pleistocene transition; Typha orientalis; stomatal index