Distribution and fluxes of marine particles in the South China Sea continental slope: implications for carbon export

Abstract. Marine particles are key vectors in the ocean’s biological carbon pump, yet their distribution, contributions to particulate organic carbon (POC) flux, and the mechanisms controlling these processes remain poorly understood in marginal seas. In this study, we investigated the spatial distribution and carbon export potential of marine particles along the continental slope of the South China Sea (SCS), using in situ imaging data from an Underwater Vision Profiler (UVP 5) collected during a June 2015 cruise. Particle abundances ranged from 0 to 783 particles L^-1 (mean: 68 ± 69 particles L^-1), with small particles (ESD < 500 µm) dominating in number (>97 %) but contributing less to POC flux (mean = 23.8 % ± 11.5 %) than large particles (76.2 % ± 11.5 %). Particle abundance and volume concentration were significantly higher in waters shallower than 200 m than in deeper waters (p < 0.01), reflecting elevated surface particles production. Estimated POC fluxes ranged from 3.4 to 302.4 mg C m^-2 d^-1, with maxima in the upper 100 m and at stations influenced by cyclonic eddies. In contrast, anticyclonic eddies were associated with reduced particle concentrations and export, likely due to stratification and nutrient limitation. The relative contribution of small particles to total POC flux increased with depth, suggesting progressive disaggregation of large particles in the mesopelagic zone. These results reveal strong spatial and vertical variability in particle-mediated carbon export and underscore the role of mesoscale physical processes in regulating carbon flux along the SCS slope.