International Journal of Marine Science, 2025, Vol.15, No.5, 255-267 http://www.aquapublisher.com/index.php/ijms 259 optimizing phosphorus acquisition strategies. Research data at a global scale show that functional genes related to phosphorus circulation in the ocean have a hierarchical distribution in different regions and depths: for example, the surface is rich in AP genes and the deep layer is rich in genes related to organic phosphine degradation (Lidbury et al., 2022). 4 Phosphorus Transport and Circulation Mechanism 4.1 Physical process: redistribution of phosphorus by ocean currents, upstreams and mixing Large-scale ocean currents and vertical mixing play a fundamental role in the spatial redistribution of ocean phosphorus. The hot salt circulation and surface circulation of seawater transport water mass containing phosphorus nutrient salts globally. The deep water in the Atlantic Ocean is rich in phosphorus produced by remineralization, and gradually spreads to the Indian Ocean and the Pacific Ocean through the ocean, making the Pacific deep water a "high stock area" of phosphorus (Teng et al., 2014). These deep high phosphorus water masses are brought back to the surface in the upflow area, becoming an important source of phosphorus for primary production of the surface. In typical upwelling systems such as Peru-Humboldt upwelling, continuous interannual coastal upwellings inject large amounts of deep phosphorus-rich water into the true light layer, supporting one of the world's highest fish yields. Observations show that the surface phosphate concentration in the upwelling area is significantly higher than that in the surrounding sea area. Compared with the oligotrophic area in the central Pacific, the phosphorus concentration in the oligotrophic area is often less than 0.1 μmol/L. The surface phosphorus caused by the upwelling along the coast of Peru can reach more than 1 μmol/L (Glock et al., 2020). This sufficient supply of phosphorus greatly promotes local phytoplankton growth and forms highly productive waters. 4.2 Biological processes: recycling of phytoplankton, bacteria and zooplankton Biological processes circulate phosphorus in the biosphere through growth-death and predation-metabolism, which is the link between inorganic and organic phosphorus banks. As primary producers, phytoplankton absorbs inorganic phosphorus from the environment to build biological tissues, a process that converts inorganic phosphorus into organic phosphorus and passes it in the food web. About hundreds of millions of tons of phosphorus are fixed to organic matter by global primary marine production every year. Some of these organic phosphorus enter a higher trophic level through the food chain (such as zooplankton and fish), achieving the flow and amplification of phosphorus in the food network, while the other part sinks into the true light layer with phytoplankton or feces particles. During the feeding and metabolism of zooplankton, some of the intake of organic phosphorus will be rapidly remineralized. The excretion and release of zooplankton converts the organophosphorus partly into dissolved inorganic phosphorus (such as phosphate) and dissolved organic phosphorus (Popendorf and Duhamel, 2015), and returns to the water body. Research points out that in eutrophied nearshore areas such as estuaries, the regenerated phosphorus contribution of microzooplankton can account for a certain proportion of the phosphorus demand of phytoplankton, thus playing an important regulatory role in the phosphorus cycle. 4.3 Deposition and resuspension process When the phosphorus in the ocean settles to the seabed in particles, it enters the sediment reservoir and may undergo burial or re-release. Under normal oxidative environments, most iron-bound phosphorus (Fe-P) exists stably in the sediment, and only a small amount is released through pore water; while organic phosphorus is buried with organic matter or is decomposed and reused by benthic organisms. In an oxidative environment, sediments tend to be a sink of phosphorus; however, in an oxygen-deficient environment, the reduction and dissolution of iron oxides releases its bound phosphorus, thus making the sediment a source of phosphorus (Yang et al., 2020). The study found that in the hypoxic sediments in the northern outer Yangtze River estuary and southern near-shore Zhejiang, the iron-bound phosphorus content was significantly lower than the surrounding aerobic zone, while the proportion of weakly adsorbed inorganic phosphorus was higher, indicating that hypoxia enabled Fe-P to be activated and converted into easily released inorganic phosphate (Liu et al., 2020). On the other hand, the resuspension process also affects the fate of sediment phosphorus. When disturbances such as
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