Particulate nitrogen and phosphorus in the East China Sea and its adjacent Kuroshio waters and evaluation of budgets for the East China Sea Shelf

Nitrogen (N) and phosphorus (P) in suspended particles are important to the cycles of N and P in marine ecosystem. Suspended particles were collected from the East China Sea (ECS) and its adjacent Kuroshio waters to investigate the composing and distribution characteristics of particulate inorganic and organic nitrogen and phosphorus (PIN, PIP, PON and POP, respectively). The particulate N and P concentrations were fairly low in the Kuroshio water but much higher in the ECS water, especially in nearshore waters. PON and PIP were the dominant forms of particulate N and P, with an exception that POP was the major form of particulate P in the Kuroshio upper water. The regime of particulate N and Pin the ECS was strongly influenced by riverine input, oceanic input, ocean current and photosynthesis. Among them, PON and POP were mainly from biogenic source, while PIN and PIP were originated from biogenic and external sources. And sedimentation, remineralization and resuspension were important influencing factors for the vertical distributions of particulate N and P. The budgets of particulate N and P for the ECS Shelf during rainy season (May-October) were also evaluated. The total particulate N and P (TPN and TPP) fluxes from oceanic input are respectively 10.99 and 2.49 times of those from riverine input. And oceanic input contains more POP, which is liable to be decomposed into phosphate, than riverine input. Furthermore, particulate nutrients fluxes from photosynthesis are the overriding source of total influxes for the ECS Shelf, accounting for 90.93% of TPN and 89.37% of TPP influxes. As for the photosynthetic fixed N and P, only 6.17% and 7.60% of them can reach the seafloor, while up to 87.73% and 60.06% of them are likely to be remineralized. The POP-rich oceanic input and the intensive photosynthesis and remineralization processes play important roles in the biogeochemical cycles of N and P in the ECS.