ocean: Surface Circulation

The surface circulation of the oceans is intimately tied to the prevailing wind circulation of the atmosphere (see wind). As the planetary winds flow across the water, frictional stresses are set up which push huge rivers of water in their path. The general pattern of these surface currents is a nearly closed system of currents, called gyres, which are approximately centered on the horse latitudes (about 30° latitude in both hemispheres). Major circulation of water in these gyres is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In the North Pacific and North Atlantic oceans, smaller counterclockwise gyres are developed partly due to the presence of the continents. These are centered on about 50°N lat. The most dominant current in the Southern Ocean is the West Wind Drift, which circles Antarctica in an easterly direction. The northern and southern hemispheric gyres are divided by an eastward flowing equatorial countercurrent, which essentially follows the belt of the doldrums. This countercurrent is caused by the return flow of water piled up along the eastward portion of the equatorial seas, and its return flow is uninhibited by the weak and erratic winds of the doldrums. Analysis of current records shows that a number of major currents, such as the Gulf Stream, have strong fast-moving currents beneath them trending in the opposite direction to the surface current. Such undercurrents, or countercurrents, appear to be as important and pervasive as the surface currents. In 1952 the Cromwell current was found flowing eastward beneath the south equatorial current of the Pacific. In 1961 a similar current was discovered in the Atlantic. See also tide.

Sections in this article:

• Introduction
• Importance of the Ocean
• The Pelagic Realm
• The Benthic Realm
• The Ocean as a Biological Environment
• Thermohaline Circulation
• Surface Circulation
• Relationship of the Ocean and the Atmosphere
• Trenches, Plains, and Ridges
• Continental Shelves, Slopes, and Rises
• The World Ocean
• Bibliography

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Geology and Oceanography