Phosphorus Cycling in the Northern South China Sea

Phosphorus was considered one of the major nutrients regulating marine primary productivity, however, the cycling of phosphorus in the ocean, particularly in the marginal sea, is not well-understood. We analyzed phosphorus concentration in sinking particulate matter collected by sediment traps moored at 2,000- and 3,500-m in the northern South China Sea (i.e., SEATS station). Aerosol, seawater dissolved and suspended particulate P are also compared, including the measured and modeled data. Results showing that phosphorus in the deep-sea sinking particles is readily reactive, averagely 17% in calcium carbonate and 50% in organic matter. In contrast to the particle sedimentation flux showing distinct seasonal variation, the proportion of phosphorus in whether the labile or refractory fractions remains relatively constant. The ratios of particulate organic carbon or nitrogen to phosphorus ratios are significantly larger than Redfield stoichiometry, implying preferential regeneration of phosphorus relative to carbon or nitrogen. The regional budget and biogeochemical cycling of phosphorus are constructed.