The Sulu Sea and the East Asian Winter Monsoon

The main feature governing the Sulu Sea climates is the East Asian monsoon. Although most of the rain falls into the Sulu Sea during the summer monsoon, the winter monsoon brings the strongest winds (Beaufort et al., 2003). The East Asian monsoon results from the difference in potential heating between the WPWP and the Asian continent. During the boreal winter, the main heating source is located in the ocean. The latent heat release associated with intense convective precipitation fuels meridional circulation. Tropical convection in the western equatorial Pacific is connected to the descending branch over the Siberian region, forming a strong local Hadley cell in the East Asian region (Zhang et al., 1997). The East Asian winter monsoon (EAWM) winds in the Sulu Sea result from the merging of the northerly East Asian monsoon with the Pacific trade winds over the South China Sea (McGregor and Nieuwolt, 1998).

Owing to those strong winds that are able to break the upper oceanic stratification, it is during the winter monsoon that the PP is highest, nowadays (de Garidel-Thoron et al., 2001). Past estimates of PP in core MD97-2141 show that PP follows closely the glacial/interglacial variation

MD90-0963

MD90-0963

Winter Monsoon Winds

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MD90-0949

MD90-0949

Winter Monsoon Winds

Figure 4: Variations of primary production estimates (solid line) in Core MD900963 (upper panel) and Core MD900949 (lower panel) compared with precession (Laskar, 1990) (doted line). Vertical lines represent Termination I and II.

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Figure 4: Variations of primary production estimates (solid line) in Core MD900963 (upper panel) and Core MD900949 (lower panel) compared with precession (Laskar, 1990) (doted line). Vertical lines represent Termination I and II.

MD97-2141

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MD97-2141

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Figure 5: Variations of primary production estimates in Core MD972141 (solid line) compared with precession (Laskar, 1990) (doted line). Vertical lines represent Termination I and II.

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Figure 5: Variations of primary production estimates in Core MD972141 (solid line) compared with precession (Laskar, 1990) (doted line). Vertical lines represent Termination I and II.

closely as evidenced by the strong 100- and 40-kyr cycles and the resemblance with S18O record obtained at the same location (de Garidel-Thoron et al., 2001). These cycles represent the influence of the high latitudes of Siberian area on EAWM. Precession cycles are also present. They are in phase with the precession and precede 818O by about 3,000 yr (Beaufort et al., 2001, 2003; Fig. 5). Therefore the precessional cycle observed in this core is again in phase with the Indian Ocean records described above, although other orbital frequencies (41 and 100 kyr) are also strongly influential here (Beaufort et al., 2003).

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