THE ROLE OF TROPICAL OCEANS IN ICE-HOUSE WORLD CLIMATE: PHYSICAL AND BIOGEOCHEMICAL ASPECTS

The Western Pacific Warm Pool (WPWP), is the centre of energy flow, material flow and genetic flow in the modern world. With the most active air-sea exchanges, the WPWP gives rise to the strongest divergent atmospheric flows associated with the Asian-Australian monsoon system and El Nino / La Nina, at least since the collision between the Asian and Australian Plates. The WPWP has experienced remarkable changes since its formation probably in late Miocene, and the sea-land distribution pattern in the tropics is the main factor controlling its existence, size, and hence its role in the Earth system. Being the global heating center at sea level, the Warm Pool transfers its excessive solar energy to high-latitude regions through oceanic and atmospheric circulation, but the efficiency is highly dependent on polar-equatorial contrast and again on sea-land pattern, as seen from the marginal sea system of the Western Pacific. Meanwhile, growing attention is being paid to tropical precessional and semiprecessional forcing of climate cyclicity in the ice-house world. Biogeochemical aspects of the role of tropical ocean in the global climate system are much less understood, but are also important. Our recent studies on ODP Site 1143 (9°N), southern South China Sea, has revealed a 0.5 myr cyclicity in the d13C records since the last 3 million years, which is well correlated with those from all the oceans, and with carbonate dissolution cycles in the tropics as well. The beginning of each cycle leads to major changes in the global climate system, such as the "Mid-Pleistocene Revolution" and "Mid-Brunches Event". Judging from its covariance with lithological and micropaleontological curves, the 0.5 myr cycles record changes in the carbonate system and upper structure of the tropical ocean, providing evidence for tropical forcing of climate system through carbon cycles. Therefore, the glacial cycles are driven not only by insolation variations at 65°N, but also by changes in the tropical carbon system.