Upwelling is a process in which deep, cold water rises towards the surface, replacing the warmer and usually nutrient-depleted surface water. This process is driven by winds blowing across the ocean surface, which push water away and cause deeper water to rise up and take its place. Upwelling can occur in the open ocean and along coastlines, and it is most closely related to human activities in the form of coastal upwelling, which supports some of the most productive fisheries in the world. Coastal upwelling occurs when the wind direction is parallel to the coastline and generates wind-driven currents. The wind-driven currents are diverted to the right of the winds in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Coriolis effect.

Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients "fertilize" surface waters, meaning that these surface waters often have high biological productivity. Therefore, good fishing grounds are typically found where upwelling is common. Coastal upwelling ecosystems, such as those along the west coast of the United States, are some of the most productive ecosystems in the world and support many of the worlds most important fisheries. Although coastal upwelling regions account for only one percent of the ocean surface, they contribute roughly 50 percent of the worlds fisheries landings.

Upwelling can also play an important role in the movement of marine animals. Most marine fish and invertebrates produce microscopic larvae which, depending on the species, may drift in the water for weeks or months as they develop. For adult marine creatures that live in shallow waters nearshore, upwelling that moves surface water offshore can potentially move drifting larvae long distances away from their natural habitat, thus reducing chances for survival.

In summary, upwelling is a process in which deep, cold water rises towards the surface, replacing the warmer and usually nutrient-depleted surface water. It is driven by winds blowing across the ocean surface and can occur in the open ocean and along coastlines. Upwelling is important for the productivity of marine ecosystems and supports many of the worlds most important fisheries.