Expansion of C4 plants in South China and evolution of East Asian monsoon since 35 Ma: Black carbon records in the northern South China Sea

The emergence and expansion of terrestrial C4 vegetation represent the most striking evolutionary adaptation of ecosystems to climate change during the Cenozoic. However, the long-term history of terrestrial C4 ecosystem expansion in East Asia remains poorly documented, and its links to tectonic and/or climate changes remain unclear due to the complexity of its forcing factors. Here, we reconstruct the long-term evolution of terrestrial C3–C4 plants biomass in South China since the late Eocene using continuous records of the stable carbon isotopic compositions (δ13C) of black carbon extracted from sediments at International Ocean Discovery Program (IODP) Site U1501 in the northern South China Sea (SCS). This study reveals remarkable stepwise expansions of C4 plants in South China at ∼20 Ma and 15 Ma with a gradual expansion trend at 7–4 Ma. We demonstrate that stepwise drying (long-term weakening of the East Asian summer monsoon and simultaneous strengthening of the East Asian winter monsoon), as well as the enhanced seasonality of precipitation, is responsible for the ecological evolution in South China since the early Miocene. Our black carbon records, combined with previous studies, indicate a coupled evolution of East Asian drying, vegetation shifts and global cooling. We suggest that the major Asian topography framework was established before the middle Miocene, and global cooling overwhelmed tectonic controls of the long-term evolution of the East Asian monsoon thereafter. This study highlights that both Tibetan uplift and global cooling have played a significant role in the long-term evolution of regional climate and vegetation.