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Why do waters above continental shelves often contain more nutrients than open-ocean waters?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

Waters above continental shelves, known as the neritic zone, typically contain higher concentrations of nutrients compared to open-ocean waters primarily due to their proximity to land. This proximity allows for the significant input of dissolved materials through riverine runoff.

These land-derived inputs, which include various minerals and organic materials, enrich the coastal waters and support higher levels of biological productivity. In contrast, open-ocean environments lack this direct, consistent supply of terrestrial nutrients. Additionally, in specific coastal regions, the process of upwelling further enhances nutrient availability by bringing nutrient-rich waters from deeper layers toward the surface, which fuels the rapid reproduction of phytoplankton and sustains complex marine food webs.123