Paleoenvironmental Changes In The Upwelling Area Of The Southwestern South China Sea During The Last 140,000 Years

The South China Sea located between Eurasia and the Pacific Ocean,and is the most important marginal sea in the western Pacific Ocean.The climate of the South China Sea is controlled by the Asian monsoon.In this paper,to reveal the marine environmental revolution in the southwestern South China Sea since the last interglacial period,we analyzed the main components,diatoms,and the isotopes of?15N,?13C and Sr-Nd of the sediment since 140 kaBP with a gravity core retrieved by SONNE 187 cruise in 2006 in the modern upwelling area in southwestern South China Sea.Main components,diatoms,Based on a comprehensive analysis of the above indexes,the sedimentary environment and paleoclimate of the South China Sea have been studied.The main results are shown as follows:The sedimentation rate of the core BIS-187-61 ranged from 4.1 cm·Ka-1 to 11.7 cm Ka-1.The mass percent of carbonate was generally high in interglacial period and low in glacial period showing typical "Atlantic carbonate type",indicating strong influence of the terrestrial input in the southwestern South China Sea.The Corg/N ratio of the core in the South China Sea was between 4 and 12,while it was less than 9 in most of the period.And the ? 15N and ?13C varied from 5.7‰ to 9.5‰ and from-23.5 ‰ to-20‰ respectively.These indicate that the organic matter was mainly from sea source and the organic matter of terrestrial sources was extremely rare.The opal in the core was mainly derived from the remaining diatom shells.The marine new productivity and primary productivity in the study area ranged from 20-80 g·m-2·yr-1 and 90-180 g m-2·yr-1,respectively.During the glacial period of MI S 2and MIS 4,the accumulation rates of organic carbon,biogenic opal and lithogenic deposition were relatively high,which were suggested to be related to the enhanced primary productivity as well as the enhanced ballast effect of lithogenic matters to sinking particles.And the enhancement was due to increasing terrestrial materials and nutrients input from the Mekong River and the Sunda shelf in East Aisa,as a result of strengthened winter monsoon and declined sea level during the ice age.During the last interglacial period MIS 5e,however,the peak accumulation rates of both biogenic and lithogenic sediments were owing to the stronger summer monsoon,which caused the strengthened upwelling off Vietnam and further increased primary productivity.