Sedimentary Record and Monsoon Activity of Core BAR9442 in Sunda Strait during 30 kaBP

Core BAR9442 (6°04.56′S and 102°25.08′E; 2 542 m water depth) is obtained below the present South Java Current, offshore the southern portion of Sumatra in the eastern Indian Ocean. Based on analyses of δ¹⁸O, AMS¹⁴C ages, grain-size distribution of standard deviation stages and relative abundance of Globigerina bulloides which commonly encountered in upwelling areas, as well as the record of clay mineral in Gingele et al.(2002), we come to the following conclusion: during the last glacial period 30-17 kaBP, when sea level was lower, terrigenous sands supply increased. Even the austral summer insulations strengthened, though the southward shift of the ITCZ in the austral summer may have been considerably restricted, where the northwest monsoon did not operate, and this would create a situation analogous to the southeast monsoon operating throughout the year, because the trade winds would blow continually across the study area. The climate was cold and dry. Under the influence of Indian northeastern monsoon, the percentage content of illite was the highest, and upwelling activity was absent and induced a low productivity. Rapid rise of sea level at the deglaciation 17-8 kaBP, the shallow connections re-opened, Makassar Strait and Lombok Strait were wider, leading to intensified surface ITF, and clay mineral became the dominated terrigenous material. The SE monsoon and NW monsoon seem to be strengthened in Early Holocene, indicating that the biannual monsoonal system was mostly intense at this time. During the Holocene (about 8 kaBP), with the sea level rising, the throughflow enhanced, and the clay minerals of the terrigenous sediments have a maximum influx while intensified NW monsoon generated a warm and wet climate.