60 / 2023-07-24 15:15:10

Biological carbon pump in the contrast ecosystems of South China Sea

POC flux,phytoplankton composition,zooplankton,fecal pellets,floating sediment trap,South China Sea

Floating sediment traps were deployed at the marginal sea of the South China Sea in the western Pacific to studied POC flux and composition of sinking particle in contrast shelf, slope and basin ecosystems, in the 4 summers during 2014 and 2018. Results showed that average integrated euphotic POC flux decreased, while the composition of sinking particles changed significantly from the shelf to slope and basin systems. Contribution of sinking phytoplankton cell decreased while zooplankton fecal pellets increased from the shelf to slope and basin systems. Diatoms was main contributor in the sinking phytoplankton in the three contrast ecosystems although diatoms-Prochlorococcus dominated in the shelf while Prochlorococcus-Haptophytes (T8) in the slope and basin water column systems. The cylindrical fecal pellets, which were produced by the dominant zooplankton group copepods, were the main contributor of zooplankton fecal pellets POC fluxes in the shelf, slope and basin systems. For the different layers of composition of sinking particles, contribution of diatoms increased from upper to depth layers. Phytoplankton regulated POC flux by aggregation and repackaging, while influencing aggregates and zooplankton fecal pellets production and sinking export. Therefore, although phytoplankton cell sinking POC flux contributed less to POC flux, it was the ultimate regulator of POC flux in the marginal seas.