The biological carbon pump (BCP) is a key mechanism for oceanic carbon sequestration, and thus significantly influencing atmospheric CO₂ concentrations. However, due to large spatial and temporal variations in biological communities and environmental gradients within marginal seas, key processes of the BCP were not well understood in these ecosystems. Here, we review BCP studies in the South China Sea, the largest marginal sea in the western Pacific, by using multiple approaches to study  plankton community dynamics, and various biologically-mediated carbon fluxes from the surface to the twilight zone. Results showed significant spatial variations in phytoplankton and zooplankton communities, with particulate organic carbon (POC) flux decreasing from shelf to slope and basin in the SCS. The composition of sinking particles also changed significantly, with the contribution of sinking phytoplankton cells (mainly diatoms) decreasing while zooplankton fecal pellets (mainly copepod-produced) increasing from shelf to slope and basin systems.

For the BCP in the twilight zone, we calculated small POC flux exported via the mixed layer pump (MLP) by biogeochemical Argo (BGC-Argo) floats, which are typically ignored in low-latitude regions. We further combined three independent approaches, including BGC-Argo observation, the cellular electron transport system (in vivo INT) and the synthesis of prokaryotic and zooplankton respiration (PR+ZR), to constrain the twilight zone remineralization in the SCS. Finally, we estimated the time-series POC flux at 1000 m by using the optical sediment trap equipped on a BGC-Argo float in the southwestern SCS, and investigate its relationship with upper ocean dynamics. Our study provides new insights of the BCP processes in the marginal sea and highlights the importance of inter-disciplinary and integrative process studies for constraining biogeochemical processes.
 

biological carbon pump,South China Sea