Spatial and seasonal dynamics of biogenic silica in a eutrophic marginal sea, the East China Sea

Abstract

Biogenic silica (BSi) is a key component of the marine silicon cycle, which is mainly driven by diatom metabolism notably contributing to primary production and export of particulate organic carbon (POC), particularly in ocean margins. Based on a large data set collected in the East China Sea (ECS), including BSi, fucoxanthin (Fuco), POC, and total suspended matter (TSM), we systematically explored the distribution and control of BSi in a typical eutrophic marginal sea. Spatially, BSi concentrations generally decreased from the shelf to the slope during all seasons, because the former is largely fed by river plumes and/or coastal currents enriched in nutrients favoring diatom growth. Abundant BSi was also observed in nearshore bottom waters probably influenced by sediment resuspension indicated by high TSM concentrations. Seasonally, BSi concentrations were on average higher in summer and autumn than in spring and winter, which reflects elevated diatom productivity during warm seasons. The BSi standing stock in the shallow water column of the ECS was significantly correlated with that of Fuco demonstrating diatoms’ dominant control on BSi dynamics. In addition, significant relationships between BSi and POC standing stocks were observed in summer and autumn, indicating the major role of diatoms in C fixation. By comparing with the northern South China Sea (NSCS), we suggested relatively small seasonal variability of BSi on the ECS shelf but significant decrease during cold seasons in the ECS slope. In the latter case, diatoms are ecologically and biogeochemically more important and more sensitive to the changing physical and/or chemical conditions than in the oligotrophic NSCS slope.