SURFACE OCEAN AND MONSOON CLIMATE VARIABILITY IN THE SOUTH CHINA SEA SINCE THE LAST GLACIATION

Changes in the Southeast Asia monsoon winds and surface circulation pa tterns since the last glaciation are inferred using multiple paleocean ographic indicators including planktic foraminifer faunal abundances, fauna and alkenones sea-surface temperature (SST) estimates, oxygen an d carbon isotopes of planktic and benthic foraminifers, and sedimentar y fluxes of carbonates and organic carbon obtained from deep-sea core SCS90-36 from the South China Sea (SCS) (17 degrees 59.70'N, 111 degre es 29.64'E at water depth 2050 m). All these paleoceanographic evidenc es indicate marked changes in the SCS ocean system over the last glaci al toward the Holocene. Planktic foraminiferal faunal SST estimates sh ow stable warm-season SST of 28.6 degrees C, close to the modem value, throughout the glacial-interglacial cycle. In contrast, cold-season S ST increases gradually from 23.6 degrees C in the last glacial to a me an value of 26.4 degrees C in the Holocene with a fluctuation of about 3 degrees C during 13-16 ka. SST estimates by U-37(k') method reveal less variability and are in average 1-3 degrees C lower than the fauna -derived winter-season SST. These patterns reveal that the seasonality of the SST is not only higher by about 3-4 degrees C in the glacial, but also a function of the winter season SST Sedimentation rates decre ase from the last glacial-deglacial stage to the Holocene due to a red uction in supply of terrigenous components, which led to an increase o f carbonate contents. Total organic carbon (TOC) contents of primarily marine sources decrease from the last glacial-deglacial to the Holoce ne. The last deglaciation is also characterized by high surface produc tivity as indicated by increased ketones abundances and high mass accu mulation rates (MAR) of the TOC and carbonates. The gradient of plankt ic foraminifer oxygen and carbon isotopes of between surface dwellers and deep dwellers increases significantly toward Termination I and Hol ocene, and is indiscernibly small in the carbon isotope gradient of be tween 14 and 24 ka, revealing a deep-mixing condition in surface layer s prior to 10 ka. The glacial-interglacial fluctuation of the carbon i sotope value of a benthic foraminifer is 0.6 parts per thousand, which is significantly larger than a global mean value. The large carbon is otope fluctuation indicates an amplification of marginal-sea effects w hich is most likely resulted from an increase in surface productivity in the northern SCS during the last glacial-deglacial stage. The multi ple proxies consistently indicate that the last glacial-deglacial stag e winter monsoon in the Southeast Asia was probably strengthened in th e northern SCS, leading to a development of deep-mixing surface layer conditions and a more efficient nutrient cycling which supports more m arine organic carbon production.