In the present work, sinking particles collected in time-series sediment traps deployed in the northern SCS from June 2009 to May 2010 were analyzed to describe the continual changes of diatom abundances and species compositions through- out one year. Sea surface Chl a values were compared with diatom and biogenic opal fluxes in the sediment traps to reveal the possible relation between the diatom downward fluxes and the phytoplankton biomass at the sea surface