Upwelling

Animation of upwelling process

Upwelling is an oceanographic phenomenon that involves the rising of deep, cold, and nutrient-rich water to the ocean surface. This process is crucial for marine ecosystems and has significant impacts on global climate and fisheries.

Mechanism of Upwelling

Upwelling occurs when winds blow across the ocean surface, pushing water away. This movement allows deeper water to rise to the surface to replace the displaced water. The primary forces driving upwelling are the Coriolis effect and Ekman transport.

Diagram of upwelling

Coriolis Effect

The Coriolis effect, due to the Earth's rotation, causes moving water to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is crucial in the formation of upwelling zones.

Ekman Transport

Ekman transport refers to the net motion of fluid as a result of a balance between the Coriolis effect and turbulent drag forces. In the context of upwelling, it results in the movement of surface waters away from the coast, allowing deeper waters to rise.

Types of Upwelling

Coastal Upwelling

Coastal upwelling occurs along coastlines where winds blow parallel to the shore. The most notable regions include the western coasts of continents, such as the California Current and the Humboldt Current off the coast of Peru and Chile.

Equatorial Upwelling

Equatorial upwelling in the Pacific Ocean

Equatorial upwelling occurs when trade winds blow across the equator, causing surface waters to diverge and allowing deeper waters to rise. This is particularly prominent in the Pacific Ocean and contributes to the high productivity of equatorial regions.

Polar Upwelling

Polar upwelling is associated with the formation of Antarctic Bottom Water, where cold, dense water sinks and spreads across the ocean floor, displacing deeper waters upward.

Formation of Antarctic Bottom Water

Ecological and Climatic Importance

Upwelling zones are among the most productive ecosystems in the world. The nutrient-rich waters support large populations of phytoplankton, which form the base of the marine food web. This, in turn, supports diverse marine life, including fish, marine mammals, and seabirds.

Impact on Fisheries

Many of the world's major fisheries are located in upwelling regions due to the abundance of marine life. The Peruvian anchoveta fishery, for example, is one of the largest in the world and is heavily dependent on the Humboldt Current upwelling system.

Climate Influence

Upwelling can influence global climate patterns. For instance, changes in upwelling intensity can affect sea surface temperatures, which in turn can impact weather patterns and climate phenomena such as El Niño.

Sea surface temperature anomalies

Related Pages

• Ocean current
• Marine ecosystem
• El Niño–Southern Oscillation
• Phytoplankton