Why the ocean's most fertile fishing grounds depend on rising deep-sea water

Nature · Published 3 October 2026 Swipe more like this →

In short: Upwelling is a vital oceanographic process where cold, nutrient-dense water rises from the depths to replace surface water pushed away by winds. This natural fertilization fuels massive blooms of phytoplankton, creating the foundation for the world's most productive marine ecosystems and supporting a significant portion of global commercial fisheries.

At its core, upwelling is driven by the interaction between wind, the Coriolis force, and Ekman transport. When winds blow parallel to a coastline, they push surface water offshore. Due to the Earth's rotation, the Coriolis effect deflects this movement, causing surface water to travel at an angle to the wind. This net movement, known as Ekman transport, creates a divergence that pulls deeper, colder, and nutrient-rich water toward the surface to fill the void.

These rising waters are essentially a cocktail of nitrate, phosphate, and silicic acid, generated by the decomposition of organic matter sinking from above. Once this nutrient-rich water reaches the sunlit surface, it triggers rapid photosynthesis by phytoplankton. This primary production cascades through the food chain, supporting zooplankton, predatory fish, marine mammals, and seabirds. While these upwelling regions cover only about one percent of the ocean's surface, they contribute roughly 50 percent of the world's total fishery landings.

However, upwelling is a double-edged sword. While it provides the essential nutrients for life, the offshore movement of surface water can also sweep away the microscopic larvae of nearshore species, potentially reducing their survival rates. Furthermore, the process is sensitive to atmospheric shifts; events like El Niño can disrupt the intensity and location of these currents, leading to devastating consequences for the ecosystems and human industries that rely on them. Understanding these dynamics is crucial, as the stability of these regions is directly tied to the health of global marine biodiversity.

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