East Asian monsoon evolution since the late Miocene from the South China Sea

The South China Sea (SCS) has become a global focus for paleoclimatic and paleoceanographic studies due to its location, which makes it highly sensitive to the East Asian monsoon and to Pacific Ocean changes. We present here a refined magnetostratigraphy for the last 6.5 Ma for Hole U1431D, which was recovered during IODP Expedition 349 in the central SCS. Magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite-bearing layer at 130.5-132.0 meters below sea floor. The greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event. Environmental magnetic results indicate that the East Asian summer and winter monsoon were stable from 6.5 to 5 Ma. The summer monsoon intensified at 5 Ma, and then weakened gradually since 3.8 Ma. In contrast, the winter monsoon weakened at 5 Ma, and has then been enhanced since 3.8 Ma and more stable from 0.6 Ma. Spectral analysis indicates that the East Asian summer monsoon was driven directly by low-latitude insolation changes before ∼3.2 Ma, and that it has been affected by both low-latitude insolation and high-latitude ice volume changes since ∼3.2 Ma.Samples and/or data provided by the International Ocean Discovery Program (IODP) were used in this research, which was supported by the National Key Research and Development Program of China (2016YFA0601903), the National Natural Science Foundation of China (41430962, 41506075, 41674069, 91528302, and 91858108), the National Natural Science Foundation of China - Shandong Province People’s Government Joint Fund for Marine Geological Process and Environment (U1606401), the National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-03), the U.S. National Science Foundation (EAR-1250444), and the Australian Research Council (grant DP160100805). Congcong Gai was further supported by the China Scholarship Council ([2017]3109)