Coastal Upwelling
Because of the Coriolis effect, seawater is moved to the right of wind direction in the north and to the left of wind direction in the south. For appropriately oriented coasts, this movement of surface water away from the shores allows deep water from below to move upward and take its place. This upward movement of cold deep ocean water near the shores of continents is called coastal upwelling.
Deep ocean water is rich in nutrients. Coastal upwelling brings nutrients to the shore and makes these areas rich in animal life. Some of the most productive fisheries in the world are areas of coastal upwelling. The rich diversity of life in these zones means that areas of ancient coastal upwelling are now important sources of organic materials that form oil, as well as some fertilizers, including phosphate.
The occurrences of coastal upwelling can be altered by El Niño events. El Niño is a periodic climate event that warms the surface waters of the Pacific. During El Niño years, an unusual build up of warm water takes place along the western shore of South America, which is one of the areas known for coastal upwelling. This build up of warm water off the coast puts a temporary halt to the upwelling and has a dramatic effect on fishing in the area. Because the upwelling ceases, nutrient-rich water from the deep does not make it to the surface, and many fish die. The diagrams below show how this works.
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During a normal year, winds represented by the white arrows blow water away from the shore of South America. As the surface water is moved to the left, cold water from below moves up to take its place. It brings nutrients that support diverse animal life. |
During an El Niño year, the winds blow differently and warm surface water pools close to the coast. The cold water does not move up from below. The nutrients that normally support rich fisheries in the area are absent and many fish die. |
