At a coastal upwelling zone, wind blow parallel to a coast, water at the ocean surface moves away from the coast and deep water rises up to take its place.
Courtesy of NOAA
There are places in the ocean where water from the deep sea travels up to the surface. These are called areas of upwelling. The deep waters can have a large influence upon life in the ocean and the climate too.
Upwelling often happens where wind blows along a coastline. The wind causes the water at the ocean surface to move perpendicular to it, away from the coast, because of a process called Ekman transport. When surface water moves away from the coast, water from deeper in the ocean rises up and takes its place.
The water that is moved up to the surface is usually cold and rich in nutrients, which come from the rotting bodies of dead sea creatures that sunk into deep water. When the deep water gets to the surface, these extra nutrients are snatched up by plankton that floats in the ocean. The number of plankton grows where there is upwelling. Tiny animals gobble up the plankton and fish eat the tiny animals. This means that upwelling areas are full of marine life. About half the fish caught in the world comes from places where there is upwelling.
Upwelling also happens as a part of El Niño (ENSO) events in the Pacific Ocean off the coast of Ecuador and Peru. This has an impact on weather, changing the pattern of precipitation in many areas of the world.
Downwelling is the opposite of upwelling - surface waters pushing down into deeper areas of the ocean. This happens when winds cause Ekman transport to push water toward a coast and then deeper in the ocean.
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