Evidence of continuous Asian summer monsoon weakening as a response to global cooling over the last 8 Ma |
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| Institution: | 1. Department of Geology and Geophysics, Louisiana State University, E-235 Howe-Russell, Baton Rouge, LA 70803, USA;2. Key Laboratory of Desert and Desertification, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China;3. Museum of Natural Science, Louisiana State University, 109 Foster Hall, Baton Rouge, LA 70803, USA;4. School of Geography Science, Nanjing Normal University, Nanjing 210023, China;1. Key Laboratory of Western China''s Environmental Systems (Ministry of Education), College of Earth and Environmental Science, Lanzhou University, Lanzhou 730000, China;2. School of Earth Sciences and Resources & Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Chang''an University, Xi''an 710054, China;3. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;1. Department of Geology and Geophysics, Louisiana State University, Baton Rouge 70803, USA;2. Department of Earth and Environment, Boston University, Boston, MA 02215, USA;3. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, USA;4. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;5. The Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;1. Institute of Earth Sciences, Heidelberg University, Heidelberg 69120, Germany;2. Department of Geography and Environmental Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, United Kingdom;3. Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam 1090 GE, the Netherlands;4. Department of Geosciences, University of Tübingen, Tübingen 72074, Germany;5. Department of Civil and Environmental Engineering & Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA;6. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China |
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| Abstract: | The Asian Summer Monsoon (ASM) is the dominant climate system of South and East Asia. However, the history of monsoon intensification and the driving forces behind it are controversial. Wind-blown sediments in mid-latitude East Asia and fluvial-derived sediments in the northern South China Sea imply contrasting ASM patterns during the late Cenozoic. Here we use pollen records from the southwest South China Sea (International Ocean Discovery Program (IODP) Site U1433) to reconstruct the ASM evolution in low-latitude Southeast Asia. A slow increase in herbaceous plants since 8 Ma indicates a persistent weakening of precipitation in Indochina, which is dominated by the ASM. This signal is closely associated with a consistent coniferous plant record, indicating a continuous cooling trend that correlates well with Sea Surface Temperature (SST) decrease in the west Pacific Ocean. We propose that the monsoon weakening resulted in as much as a ~ 25% reduction in precipitation over the past 8 Ma in response to the Northern Hemisphere glaciation/global cooling, with some of the increase in conifers being linked to uplift of the Vietnamese Central Highland and the SE flank of the Tibetan Plateau in Yunnan and northern Vietnam. |
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