East Asian monsoon variations during Oxygen Isotope Stage 5: evidence from the northwestern margin of the Chinese loess plateau |
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| Institution: | 1. Department of Geography, Lanzhou University, Lanzhou, Gansu 730000, People''s Republic of China;2. Department of Geography, University of Liverpool, Roxby Building, Liverpool, L69 3BX, UK;3. Department of Earth and Environmental Studies, Montclair State University, Upper Montclair, NJ 07043, USA;4. Beijing Institute of Geology, CAS, Beijing 100029, People''s Republic of China;1. Key Laboratory of Surficial Geochemistry, Ministry of Education, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210026, China;2. School of Geographic and Ocean Science, Nanjing University, Nanjing 210026, China;1. Ministry of Education Key Laboratory of Surficial Geochemistry, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;2. Department of Geography, University of Wisconsin Madison, 160 Science Hall, 550 N. Park St., Madison, WI 53706, USA;3. School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China;1. Key Laboratory of Salt Lake Geology and Environment of Qinghai Province, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China;2. SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi''an 710075, China;3. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;4. College of Biology and Geography, Qinghai Normal University, Xining 810008, China;5. College of Resources and Environment, Linyi University, Linyi 276000, China;6. University of Chinese Academy of Sciences, Beijing 100049, China;1. Key Laboratory of Western China’s Environment System (Ministry of Education), Lanzhou University, Lanzhou 730000, China;2. Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;3. Department of Geological Sciences, California State University, Northridge 91330-8266, USA;4. Department of Environmental Sciences, Rochester Institute of Technology, Rochester 14623, USA;5. Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence 02912, USA;6. Department of Chemistry, Lanzhou University, Lanzhou 730000, China;7. School of Geography, Geomatics and Planning, Jiangsu Normal University, Xuzhou 221116, China;8. Department of Geography and Environmental Sciences, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK;1. Key Laboratory of Western China’s Environment Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, Gansu 730000, China;2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, P. O. Box 17, Xi’an 710061, China;3. Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, USA |
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| Abstract: | We present the results of high-resolution multi-proxy climate studies of the S1 palaeosol, corresponding to oxygen isotope stage (OIS) 5, from the northwestern margin of the Chinese Loess Plateau area. Here, S1 is much thicker (ca. 6–8 m) than in the central Loess Plateau areas (ca. 2 m), where most previous studies have been conducted. Hence, much higher-resolution stratigraphic studies are possible, yielding more insight into the temporal variations of the East Asian monsoon during MIS 5. The frequency-dependent magnetic susceptibility, as well as the concentration of secondary carbonate, is used as an indicator of the summer monsoon intensity, and the median particle size as an indicator of the winter monsoon intensity. The results suggest that the northwestern margin of the Chinese Loess Plateau experienced the strongest summer monsoon intensity in sub-stage (OISS) 5e and the weakest in OISS 5a, among the three warmer periods during stage 5. The summer monsoon was weaker in OISS 5b than in OISS 5d. A dusty interval interrupted the second warmer period (5c) and a soil-forming event interrupted the first colder period (5d). The results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been proportionately opposite. For example, the weakest summer monsoon occurred in OISS 5a during which the winter monsoon was not the strongest. We further conclude that the winter monsoon during the last interglacial was probably driven by global ice volume fluctuations, while the summer monsoon was primarily controlled by the northern hemisphere solar insolation and was probably modified by a feedback mechanism. That is, the climatic buffering effect of low-latitudinal oceans may have distorted the response of the summer monsoon to insolation variations. Finally, our results do not show the degree of climatic instability comparable to that recorded in the GRIP ice core for the last interglacial (OISS 5e), even though the study area is situated in a region which has been sensitive to climatic changes. |
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