Pleistocene paleoceanography of the South China Sea: Progress over the past 20years

Abstract

Abstract The South China Sea (SCS) has become one of the foci in paleoceanographic research and hydrocarbon explorations over the last 20 years. Over the period, at least 16 international cruises including ODP (Ocean Drilling Program) Leg 184 have investigated the SCS, and more than 2000 exploratory wells have been drilled. The present paper attempts to synthesize progress in Pleistocene paleoceanography. Because of the high depositional rates and favorable carbonate preservation, the SCS keeps valuable paleoceanographic archives for the low latitude Pacific region, which have helped to uncover potential ties between the low-latitude oceanic biogeochemical evolution and step-wise development of the boreal ice sheet. It has been found that the 1.6 Ma event marked a reorganization of the oceanic carbon reservoir associated with the restructuring of the Southern and the tropical Pacific Ocean. The MPT (Mid-Pleistocene Transition) and MBE (Mid-Brunhes Event) centered at 0.9 Ma and 0.4 Ma, respectively, were preluded by carbon isotope maxima δ13Cmax-III and δ13Cmax-II, suggesting that major steps in the ice-sheet development were preceded by significant changes in oceanic biogeochemistry. The late Pleistocene records have demonstrated the amplifying role of the SCS in responding to glacial cycles, as the amplitudes of SST and δ18O variations have been significantly amplified in the SCS as compared with the open ocean at the same latitudes. The amplification is ascribed to its semi-enclosed morphology and the prevailing monsoon climate. The closure of the southern margin during glacial times led to stratification of the upper waters and specific faunal changes in the southern SCS. The seasonally reversing monsoon winds not only drive the surface circulation, but also the biological production, the N–S gradient in oceanography, and the sediment transport dynamics such as the asymmetric growth of the Mekong River delta. Because of its distinguished position in the low latitudes between the largest continent and the largest ocean, the SCS provides important insight into the mechanism of environmental evolution with regards to ocean–continent or high–low latitude interactions.