Reconstructing atmospheric CO2 during the Plio–Pleistocene transition by fossil Typha

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.