Variation of Diatoms in the Sinking Particles and the Paleoceanographic Implication in the northern South China Sea: One-year Sediment Trap Mooring Observation

Temporal and vertical variations of diatoms in the sinking particles collected by time-series sediment traps during 2009-2010 in the northern South China Sea were studied, and the environmental controls on the diatom distributions were discussed. The results showed that diatom productivity was apparently higher in winter than in summer in the northern South China Sea, attributed to a positive response of diatom growth to increased nutrient supply from the subsurface as a result of enhanced vertical mixing and monsoon induced upwelling off NW Luzon in winter. On the contrary, strong stratification and the southwest monsoon induced basin-scale anticyclonic circulation resulted in low productivity of diatoms in summer. In addition to seasonally changing oceanographic environment, short-term environmental changes, such as meso-scale eddy activity and heavy aerosol deposition from the Asian dust storms, were also able to rapidly and strongly influence the diatom growth. A smoothed variation of diatom and opal fluxes without abrupt changes due to short-term diatom bloom in the surface was found in the deep northern South China Sea, together with an increased disagreement of diatom cell abundance and opal flux. The present study on diatoms retrieved from time-series sediment traps suggested that diatoms produced in winter were the major contributor to the diatoms preserved in sediment in the northern South China Sea, and the paleocenographic reconstruction based on sediment diatoms and biogenic opal in the northern South China Sea was more likely to reflect the winter environmental changes in the past.