Records of Paleo-Monsoon of Core BAR9427 in Northeastern Indian Ocean during Last Glaciation

The climate was obviously instable in the last glacial cycle, especially in the Marine Oxygen Isotope Stage 3. The South Asian monsoon activities conflict with the glaciation and interglaciation rule. The paleo ceanographic study of the core BAR9427 from the south of the Andaman Sea, the Great Strait at the northwest terminal of the Sumatra Island in the northeast Indian Ocean, and its comparison with that of the nearby cores MD77181 and MD81349 in the Bay of Bengal, reach the following conclusions: the northeastern monsoon was strong in intensity with the active upwelling and the relatively high paleoproductivity over the studied area in the MIS 2 of the last glaciation. Meanwhile, the sea surface salinity increased due to the strong evaporation near the shore region. The southwestern monsoon was strong over the studied area in the early and late MIS 3. The easterly southwestern monsoon current increased the salinity in the middle of the Bay of Bengal. However, the salinity decreased greatly in the north of the Bay of Bengal because of both the monsoon rain and the influx of a mass of fresh water. In addition, the salinity was lower in August than in February. The southwestern monsoon activities follow the 23 ka precession cycle, a phenomenon also discovered in the Tibetan plateau, the loess and desert fields of China, and the Arabian Sea.