One of the major components of the tropical climate system is the Asian monsoons, which result in a differential land-sea sensitive heating, inducing seasonal reversals in wind direction and producing intensive rainfall during the summer. Numerous paleoclimatic studies (Clemens and Prell, 1991; Wang et al., 1999), based on different proxies, have led to the reconstruction of the strength of the paleomonsoon intensity. Such reconstructions have shown that variations in summer monsoon intensity are mainly forced by the contrast in insolation between the Northern and Southern Hemispheres (Clemens et al., 1991). When the summer insolation in the Northern Hemisphere decreases relative to present-day conditions, the low-pressure surface cell over the Asian continent is weaker. This results in a reduced land-sea pressure gradient and a weak summer monsoon, whereas increased summer insolation strengthens the summer monsoon (Clemens and Prell, 1990; Emeis et al., 1995).
On a regional scale, the climate of the South China Sea (SCS) and the ambient land masses is dominated by the East Asian monsoon, which represents an important factor driving weathering and erosion of the eastern Asian region. On geological timescales, changes in the strength of the summer monsoon rainfall and the winter monsoon wind have led to a modification of the chemical and physical weathering intensity of the East Asian continent (e.g., the Pearl River Basin) and of the eolian dust transportation patterns. Therefore, SCS sediments as well as the loess plateau provide records of the variability of the intensity in the erosion of the Asian continent, which is in turn related to paleoclimatic and paleoenvironmental variations affecting southeast Asia. Past East Asian monsoon variations have been extensively studied from Chinese loess plateau deposits using several proxies, such as grain size, magnetic susceptibility, or mineral distribution (An et al., 1990; Xiao et al., 1995; Chen et al., 1997; Lu et al., 2000; Porter and An, 1995). Similar studies of deep-sea sediments of the SCS, however, have seldom been performed (Wang et al., 1999).
The main purpose of this pilot study is to reconstruct from deep-sea sediment the paleoenvironmental changes affecting the continent by (1) characterizing the mineralogy, the grain size distribution, and the geochemistry of major elements in the Pleistocene sediments from the northern part of the SCS over the last 1.1 Ma, (2) identifying the sources of these sediments, and (3) establishing the relationship between the variability of siliciclastic sediments and the climatic changes including monsoon and sea level changes during the Quaternary.