International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 294 amounts of phosphorus. In the upwelling area, due to the influx of deep phosphorus-rich seawater, the surface phosphorus is relatively abundant, maintaining high primary productivity. However, in some semi-enclosed sea areas with severe stratification (such as deep water anoxic basins), phosphorus accumulates in large quantities in the deep layers but cannot be replenished to the surface, resulting in a pattern of phosphorus-poor upper layers and phosphorus-rich deep layers (Zeng et al., 2022). Due to the differences in hydrological, topographic and biological factors, the phosphorus cycle in different ecological zones shows unique dynamics, which require separate studies for specific environments. 3 Major Sources of Marine Phosphorus 3.1 Terrestrial inputs: river runoff, agricultural, and industrial discharges Land-based input is an important exogenous source of Marine phosphorus, among which river runoff plays a key role. Phosphate released from the weathering of terrestrial rocks flows into the ocean via rivers. Meanwhile, a large amount of phosphorus-containing pollutants produced by human agricultural fertilization, animal husbandry and industrial life emissions are also carried into the coastal areas through rivers. The phosphorus output in modern river basins has significantly increased compared to the natural situation, resulting in a significant increase in the phosphorus load of estuarine and nearshore water bodies (Jin et al, 2024). A portion of the phosphorus transported by rivers exists in dissolved form and can be directly utilized by Marine organisms. Another part was adsorbed on the sediment and deposited in estuaries and continental shelves in the form of granular phosphorus (Wang et al., 2021). An appropriate amount of phosphorus input can support high primary productivity and fishery resources along the coast, but excessive phosphorus can cause environmental problems such as eutrophication, algal blooms and even hypoxia. Therefore, the input of land-based phosphorus plays a profound role in regulating the coastal ecosystem, and its control is crucial for maintaining the Marine ecological balance. 3.2 Atmospheric deposition and phosphorus transport via dust In the sea far from the shore, people often rely on things that fall from the sky to get some nourishment. The wind sweeps up dust from the arid continent, which contains phosphorus mineral particles. After transoceanic flight, it falls into the sea, adding a handful of phosphorus to the surface water (Dam et al., 2021). The example in the North Atlantic is quite intuitive: Sahara dust not only brings phosphorus but also iron, benefiting phytoplankton. However, not all the phosphorus that falls is effective. Most of the phosphorus in mineral dust is in insoluble inorganic form. However, during flight, acidic gases are encountered. Some of the phosphorus is "pre-treated" and becomes soluble, making it easier for organisms to utilize (Hu et al., 2025). In recent years, the climate has been changing, and so has the dust: drier continents and stronger winds may increase the output of dust. However, when the temporal and spatial distribution of rainfall changes, the rhythm of sedimentation also becomes disrupted. The result is that the way and intensity of phosphorus reception in the open sea areas have been rewritten, and primary productivity and carbon sink capacity may also fluctuate accordingly. 3.3 Contributions from seafloor geological processes and sediment release There are also mechanisms for the release of phosphorus through geological and sedimentary processes within the ocean. Submarine volcanic eruptions and hydrothermal activities release phosphorus-containing substances into seawater. Although this part of the flux is relatively small and localized, it may contribute to the surrounding phosphorus levels in areas with frequent volcanic activities (Liu et al., 2023). More commonly, there is the re-release of phosphorus from sediments: the ocean uses biological pumps to deposit large amounts of phosphorus on the seabed, and sediments become huge phosphorus reservoirs. When the bottom water body is hypoxic, phosphorus combined with oxides such as iron in the sediment is desorbed due to reduction and diffuses into the overfacing seawater (Guo et al., 2020); Phosphorus produced by the decomposition of organic matter can also be released into the water column from pore water. The disturbance of benthic organisms can also bring out some buried phosphorus and integrate it into the cycle. However, most of the phosphorus that enters the sediment is eventually fixed and buried in the geological layer in the form of minerals, so the seabed process is generally the "destination" of Marine phosphorus. Only a small amount of sedimentary phosphorus released under special conditions remains an indispensable part of the nutrient supply in some local sea areas.
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