Development of the East Asian summer monsoon: Evidence from the sediment record in the South China Sea since 8.5 Ma Shiming Wan a,b , Anchun Li a, ⁎ , Peter D. Clift c , Hengyi Jiang a,b a Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China b Graduate school, Chinese Academy of Sciences, Beijing 100039, China c School of Geosciences, University of Aberdeen, Meston Building, Kings College, Aberdeen, AB24 3UE, United Kingdom Received 22 September 2004; accepted 26 June 2006 Abstract 128 samples from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea were analyzed for grain size, clay minerals, biogenic opal content and quartz in order to reconstruct changes in East Asian monsoon climate since 8.5 Ma. An abrupt change of terrigenous mass accumulation rate (MAR), clay mineral assemblage, median grain size and biogenic opal MAR about 5.2 Ma suggests that between 8.5–5.2 Ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern Vietnam. A simple model of East Asian summer monsoon evolution was based on the clay/feldspar ratio, kaolinite/chlorite ratio and biogenic opal MAR. The summer monsoon has two periods of maximum strength at 8.5–7.6 Ma and 7.1–6.2 Ma. Subsequently, there was a relatively stable period at 6.2–3.5 Ma, continued intensification about 3.5–2.5 Ma, and gradually weakening after 2.5 Ma. Since 1 Ma the monsoon has intensified, with remarkable high-frequency and amplitude variability. Simultaneous increase in sedimentation rates at ODP Sites 1143, 1146 and 1148, as well as in MAR of terrigenous materials, quartz, feldspar and clay minerals at ODP Site 1143 at 3.5–2.5 Ma, may be the erosional response to both global climatic deterioration and the strengthening of the East Asian summer monsoon after about 3–4 Ma. © 2006 Elsevier B.V. All rights reserved. Keywords: East Asian monsoon; South China Sea; Tibetan Plateau; Mineral composition; ODP Leg 184 1. Introduction Cenozoic uplift of the Himalayas and Tibetan Plateau has been proposed to profoundly affect the regional and global climate, and to have contributed to the inception of the Asian monsoon and Northern Hemisphere glaciation (Quade et al., 1989; Raymo and Ruddiman, 1992; Harrison et al., 1993; Kutzbach et al., 1993; Molnar et al., 1993; Raymo, 1994; Li, 1996; An et al., 2001). The Asian monsoon system is a major component of both regional and global climate (Webster et al., 1998). Past fluctuations of the East Asian summer and winter monsoons over long time scales (>1 m.y.) have been studied using the loess– paleosol sequences in the Chinese loess plateau (Porter et al., 1992; Ding et al., 1994, 1999; Vandenberghe et al., 1997; Liu and Ding, 1998; An, 2000; An et al., 2001; Qiang et al., 2001; Guo et al., 2002; Sun and An, 2002). By comparison, similar studies of deep-sea sediments from the South China Sea, which is the main sediment sink for fluvial materials from East Asia and Palaeogeography, Palaeoclimatology, Palaeoecology 241 (2006) 139 – 159 www.elsevier.com/locate/palaeo ⁎ Corresponding author. Fax: +86 532 8289 8526. E-mail address: acli@ms.qdio.ac.cn (A. Li). 0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.06.013