The Shipboard Scientific Party of Leg 184 sought to better understand the history and variability of the Asian monsoon system, which is a major component of the regional climate of Asia as well as of global climate. Evolution of monsoonal climates in southern Asia is linked to the growth of the Himalayan-Tibetan orogen, the opening and closing of marginal seas, and changes in global climate, including atmospheric CO2 levels. The South China Sea (SCS) experiences both summer and winter monsoons, and its sediments record the erosion and weathering of tectonic orogens as well as changes in global and regional climate. Hence, Leg 184 was designed to recover sediment sections in the southern and northern SCS to provide records capable of unraveling both the regional and global climate changes on a variety of time scales ranging from millennial to tectonic.

The circulation patterns of the Asian summer and winter monsoons dominate the seasonal patterns of winds, precipitation, and runoff and determine, in part, the character of land vegetation over southern and eastern Asia (Hastenrath, 1991; Hastenrath and Greischar, 1993; Webster, 1987; Webster, 1994; Webster et al., 1998, Lau and Yang, 1997). The winter monsoon is characterized by continental cooling and development of high pressure over northern Asia, northeast winds across the South China Sea (which intensify during cold surges), and increased rainfall in the Austral-Asian equatorial zone (Fig. 1A, 1C). Similarly, northwest winds are found in the Indian Ocean, although they are not accompanied by cold surges. The summer monsoon circulation is characterized by continental heating, the development of low pressure over Tibet, and southerly winds across all of southern Asia. In the South China Sea, the summer monsoon is marked by moderate (5 m/s) southerly winds, weak to moderate upwelling off Vietnam, and high precipitation over southern and eastern Asia (Fig. 1B, 1D). In contrast, the summer monsoon exhibits strong (10 m/s) southwesterly winds and intense upwelling in the Arabian Sea. The location of the South China Sea between East Asia and the maritime continent is ideal to record the paleoceanographic responses to both winter and summer monsoons (Figs. 1, 2).

Tectonic Framework of the South China Sea

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