Published on: 12/4/2020 12:31:20 AM

When the wind blows parallel to a coastline, surface waters are pushed offshore and water is drawn from below to replace the water that has been pushed away. The upward Movement of this deep, colder water is called upwelling.

The deeper water that rises to the surface during upwelling is rich in nutrients. These nutrients 'fertilize' surface waters encouraging the growth of sea weed and phytoplankton. These phytoplankton serve as the ultimate energy base for large animal populations higher in the food chain, providing food for fish, marine mammals, sea birds, and other critters. Because of this, coastal upwelling ecosystem, such as along the west coast of the U.S., are some of the most productive ecosystems in the world and support many of the world's most important fisheries. Although coastal upwelling regions account for only 1% of the ocean surface, they contribute roughly 50% of the world's fisheries landings.

Types of Upwelling

Upwelling is of two main types as follows

1. Divergence - dependent upwelling or equatorial upwelling

2. Ekman transport - dependent coastal upwelling


The divergence of surface ocean currents causes upwelling of cold deep water along the eastern margins of each ocean basins or along the western coasts in the equatorial region. The trade winds drive the equatorial currents (N and S equatorial currents) toward west in each ocean. The Ekman transport moves the water to the right of wind direction in the NH or to the north side of equator towards more northerly region, and to the left or towards more southerly areas in the SH. This cause deficit on the eastern sides of ocean basins, with the result cold deep water comes upward to compensate the loss of surface water. Such type of upwelling of cold deep water may be called divergence - dependent upwelling, which is also called equatorial upwelling because it occurs in the equatorial regions of the ocean.

The second type of upwelling is coastal upwelling caused by Ekman transport. such upwelling always occurs when the winds blow parallel to the coasts and coasts are placed to the left of wind direction in the NH, and to the right of wind direction in the SH. In fact, coastal upwelling occurs when coastal water is driven away from below moves upward vertically to fill up the void.

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 distance away from their natural habitat, thus reducing chances for survival.

In some ways, upwelling can be a mixed blessing to coastal ecosystems. It can infuse coastal waters with critical nutrients that fuel dramatic productivity, but it can also rob coastal ecosystem of offspring required to replenish coastal populations.