What Is Upwelling?

Upwelling drives cooler, denser water from the lower surface of the ocean to the upper surface.
Upwelling drives cooler, denser water from the lower surface of the ocean to the upper surface.

Upwelling is a phenomenon that occurs in the ocean when the strong wind drives cooler, denser water from a lower surface in the ocean to the upper surface. In the process, the warmer water which is on the surface is moved to the bottom and is replaced by the cooler waters. The cooler, dense water that is moved during the upwelling process is usually rich in nutrients, unlike the water on the surface whose nutrients are usually exhausted by marine life. The intensity of the process depends on how strong the wind is. In some regions, the upwelling process is seasonal. In these regions, the marine productivity is also seasonal.

Mechanisms Behind Upwelling

The three mechanisms behind the upwelling process include the winds, the Ekman transport, and the Coriolis effects. The three mechanisms are important in the occurrences of different forms of upwelling. Generally, the wind blows across the water surface, leading to the water mixing with the wind, and eventually leading to the upwelling process. The wind results in the transportation of water at a rate of 90 degrees away from the wind’s direction, a phenomenon brought about by Coriolis effects and Ekman transport. The Ekman transport is responsible for the approximately 45 degrees movement of water layer on the surface from the direction of the wind. The movement of water causes friction between the topmost layer and the layer below. This friction causes the subsequent layers to move in the similar direction as the topmost layer, resulting in a spiral-like movement of water. The Coriolis forces are responsible for the direction to which the water moves. If the upwelling is occurring in the northern hemisphere, the Coriolis force moves the water to the right-hand side of the wind while in the southern hemisphere the water is moved to the left-hand side of the direction of the wind

Types of Upwelling

There are several types of upwelling including the coastal upwelling, broad-diffusive upwelling, topographically-associated upwelling, eddies-associated upwelling, and wind-driven upwelling on a large scale.

Eddies occur when waters in a water body move in a circular motion, causing an upwelling. This phenomenon, is, however, not common like the other types of upwelling. The most popular of the types of upwelling are as discussed below.

1. Coastal Upwelling

The most popular upwelling is the coastal upwelling. It also directly affects human activities in the marine environment. Most of the popular fishing grounds in the oceans are dependent on coastal upwelling. This type of upwelling is also indirectly affected by the rotation of the earth. Water currents are pushed by strong intensity winds. The Coriolis effect forces the waters to divert rightwards from the direction of the wind in the northern hemisphere and leftwards in the southern hemisphere. Ekman forces are responsible for the movement of waters at 90 degrees. The rate at which the entire upwelling process occurs is usually 5 to 10 meters per day. The rate entirely depends on the intensity of the wind.

The most popular upwelling coastal regions include the Canary Current which influences upwelling in the coastal region of North Africa, the Benguela Current of South Africa, the California Current which influences upwelling off the Californian and the Oregonian coastlines, and the Humboldt Current off coastlines of Peru, Chile, and the Ecuador. The presence of dense phytoplankton on the coast may signify the occurrence of coastal upwelling in the region.

2. Equatorial Upwelling

The occurrence of the upwelling at the equator is different from its occurrence at other regions. The process at the equator is influenced by Intertropical Convergence Zone. There are usually no Coriolis forces at the equator. If at all the forces responsible for the upwelling process are present at the equator, there are usually very minimal. Upwelling still occurs despite the absence of Coriolis forces. Upwelling at the equator pushes water to different directions in the two hemispheres. In the northern hemisphere, the waters are pushed rightwards from the direction of wind whereas in the southern hemisphere they are pushed leftward from the direction of the wind. Upwelling at the equator has only been observed in the Pacific and Atlantic oceans. In the equatorial region of the Pacific Ocean, there is usually a high concentration of phytoplankton. This is evidence enough that upwelling occurs at the equator.

3. Large Scale Upwelling

When the westerly winds with high intensity blow in the area surrounding Antarctica, it increases the water flow on the northern side of Antarctica. The water from this upwelling is drawn from greater depths because there are no masses of land between the tip of the Antarctic Peninsula and South America. This type of upwelling is usually popular in the western coasts of the continents of North and South America, South Australia, Southwest Africa, and Northwest Africa. These regions are all associated with the circulation of the oceanic subtropical high-pressure.

Significance Of The Upwelling Process

As earlier stated, the water which is upwelled is usually rich in nutrients. Among the most popular nutrients in the upwelled waters are nitrates, phosphates, and silicic acid. These nutrients are usually generated from decomposition of dead decaying organic matter. The nutrients are responsible for the development of marine plant life. The primary producers, such as the phytoplankton, are the sole beneficiaries of the upwelling process. These nutrients, together with absorbed CO2, are used to hasten the process of photosynthesis. Primary productivity is increased with the increasing upwelling regions. Increase in primary productivity directly translates to increased viable fishing grounds. Upwelling regions constitute approximately half of the most viable land in the marine regions. Upwelling is also responsible for the movement of marine animals. This is more applicable to marine animals that are mostly invertebrates. It helps the animals discover new viable breeding grounds and calmer dwelling places.

Negative Effect Of Upwelling

While the upwelling regions are important for marine productivity, the process has been known to reduce chances of survival for some marine species. The upwelling regions attract more commercial fishers who may exhaust and significantly reduce the marine life of the region. The overfishing in the upwelling region will lead to a depletion of one or a variety of species of marine animals, subsequently leading to an ecosystem collapse. Also, if the water is moved, it occasionally moves with larvae or eggs of the egg-laying species. Scattering the eggs and larvae to different locations from the breeding regions disrupt the breeding process.


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