Patterns of Circulation. Vertical Structure. Wind-Driven Currents and Ekman Transport. Wind-Driven Surface Currents. Western Boundary Currents.
Ocean Conveyer Belt. Where Ekman transport moves surface waters away from the coast, surface waters are replaced by water that wells up from below in the process known as upwelling. This example is from the Northern Hemisphere. In some coastal areas of the ocean and large lakes such as the North American Great Lakes , the combination of persistent winds, Earth's rotation the Coriolis effect , and restrictions on lateral movements of water caused by shorelines and shallow bottoms induces upward and downward water movements.
As explained above, the Coriolis effect plus the frictional coupling of wind and water Ekman transport cause net movement of surface water at about 90 degrees to the right of the wind direction in the Northern Hemisphere and to the left of the wind direction in the Southern Hemisphere.
Coastal upwelling occurs where Ekman transport moves surface waters away from the coast; surface waters are replaced by water that wells up from below. Where Ekman transport moves surface waters toward the coast, the water piles up and sinks in the process known as downwelling. This high level of productivity can be seen by looking at levels of chlorophyll in the ocean.
The abundance of phytoplankton surrounding the Galapagos Islands provides food for many species of fish, birds and mammals and creates some of the richest fishing grounds in the world. Previous: Oceanography — The Humboldt Current.
Next: Oceanography — Oceanography Quiz. Back Close. At this time, a strong easterly Trade wind blows , and low SSTs prevail along the equator. Fig 1. Ekman pumping along the equator. Upwelling is a process in which current s bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth. The Earth rotates on its axis from west to east.
Because of this rotation, winds tend to veer right in the northern hemisphere and left in the southern hemisphere.
This is known as the Coriolis effect and is largely responsible for upwelling in coast al regions. The Coriolis effect also causes upwelling in the open ocean near the Equator. Trade wind s at the Equator blow surface water both north and south, allowing upwelling of deeper water.
The wind patterns generated during slow-moving cyclone s can also blow surface water aside, causing upwelling directly beneath the eye of the cyclone. The colder water eventually helps to weaken the cyclone. Effects of Upwelling Biodiversity and productivity Because the deep water brought to the surface is often rich in nutrient s, coastal upwelling supports the growth of seaweed and plankton. These, in turn, provide food for fish, marine mammal s, and birds.
A 25,square-kilometer 10,square-mile region off the west coast of Peru, for example, undergoes continual coastal upwelling and is among the richest fishing grounds in the world. The transition zone between warm surface water and cold deep water deepens.
The combination of weak winds and deeper water limits upwelling. The reduction in nutrient-rich water leads to a lower fish population in the area, and therefore to a smaller fish crop. Animal movement Upwelling affects the movement of animal life in the area.
Tiny larva e—the developing forms of many fish and invertebrates—can drift around in ocean currents for long periods of time. A strong upwelling event can wash the larvae far offshore, endangering their survival. Coastal climate The cold water welling up to the surface cools the air in the region.
This promotes the development of sea fog.
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