Abstract
The Asian monsoon variations under global temperature changes during the Pliocene are still debated. Here we use a sedimentary record of phytoliths (plant silica) from the Weihe Basin, central China, to explore the history of C4 grasses and quantitatively reconstruct the Asian monsoon climate since the late Miocene. Our results show that C4 grasses have been a dominant grassland component since ~11.0 Ma. A subsequent marked decrease in warm- and humid-adapted C4 grasses and an increase in cool- and dry-adapted C3 grasses occurred in the Pliocene, ~4.0 Ma; the phytolith-based quantitative reconstruction of mean annual precipitation marked a decrease from 800~1673 mm to 443~900 mm, indicating a reduction in Asian monsoon rainfall in the Pliocene. Our newly obtained records conflict with the hypothesis that the growth of the Tibetan Plateau strengthened the Asian monsoon rainfall. Nevertheless, they emphasize the importance of global temperature as a determinant of Pliocene Asian monsoon variations.
Highlights
The Asian monsoon variations under global temperature changes during the Pliocene are still debated
A similar debate exists for the Chinese Loess Plateau (CLP), where δ13C profiles of pedogenic carbonate suggest that an expansion of C4 grasses occurred at ~4.0 Ma4,5, which has been interpreted as increased warm-season precipitation (WSP) in East Asia[5]
Our results reveal that C4 grasses were moderately abundant to very abundant in the study area at ~11.0 Ma, which is most likely the earliest fossil record of C4 grassland in East Asia
Summary
The Asian monsoon variations under global temperature changes during the Pliocene are still debated. If it was possible to evaluate the ecological role (from non-dominant to dominant) played by each clade of grasses during the expansion of C4 grasses, the corresponding environmental controls and driving mechanisms could be identified, which would eventually lead to a better understanding of the linkages between C4 grasses and late Neogene climate change. For this reason, the study of phytolith assemblages as a direct record of late Neogene plant communities has attracted increasing interest for understanding the origin of C4 expansion[11]. As an alternative to stable carbon isotope (δ13C) analysis, fossil phytoliths can provide detailed information on C3 (forests/shrubs/C3 grasslands) and C4 (Chloridoideae-dominated/Panicoideae-dominated grasslands) vegetation[12], providing detailed information on climate change
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