Program

The particle fluxes obtained by sediment traps at 1000 m in the slope of northwestern South China Sea (SCS) from July 2012 to June 2013 show distinct seasonal variations. The total flux varies from 154.9 to 1244.8 mg/m2/d, while the ranges of Particulate Organic Carbon (POC), CaCO3 and Opal are 5.8-30.5 mg C/m2/d, 37.3-185.2 mg/m2/d, 18.5-152.7 mg/m2/d, respectively. Although 46-76% total flux is contributed by lithogenic matter, the percentage of terrigenous POC calculated from the two-end model based on C/N ratio only accounts for ~10%, showing marine material is the main source for mesopelagic POC. The temporal change of particle fluxes may be controlled by various physical processes in the upper ocean, such as: (1) Enhanced mixing process during the northeastern monsoon period which induced more nutrient injection to fuel primary production and thus high flux peak in winter. (2) Subsurface upwelling near Hainan island which may served as the main cause of particle flux peak in July. (3) Atmospheric deposition which may stimulate a large calcifier bloom, resulting in high particle fluxes in the mesoplegic ocean. In the perspective of export efficiency, ballast effect is considered to be one of the determining factors. The Eeff ratio (1000FPOC/NPP) and Rain Ratio (POC/PIC) indicated that the efficiency of the biological pump is higher during upwelling period than northeastern monsoon period.