Ocean Surface Currents
As you learned earlier, the ocean is divided into two general layers based on temperature—the relatively warm surface and the cold deep. While motion of the cold deep water is driven by density differences, the movement of the surface waters is driven mainly by wind. In turn, the winds are caused by uneven heating of Earth’s surface, which demonstrates one more way the oceans and the atmosphere are connected. You will learn first about the motions of the ocean surface waters.
Like movement of the atmosphere, the ocean surface waters move in predictable patterns around the globe. The map shows the major ocean surface currents. One of these currents, named the Agulhas Current, was a major obstacle to early shipping exploration from the west to the east around Africa. It would drive ships back westward and prevented Portugal from being able to establish a shipping route to India in the early centuries of shipping exploration. Click through the tabs below to learn about the ocean surface currents.
Gyres and Eddies
The ocean surface currents move in response to the winds, but they are also impacted by barriers to flow, like the continents and the Coriolis effect. The wind, in combination with Earth’s rotation, creates circular patterns of surface water flow called gyres. A gyre is a large circular flow of ocean surface water, and most of the water in the top 400 meters of the oceans flows in this fashion. Sometimes currents collide and create eddies, which are swirling rings of water. They can be only a few centimeters to hundreds of kilometers in diameter.
Eddy Formation
Watch the circular flow of water just under the southern tip of Africa—this is the formation of an eddy. Eddies like this one are characterized by turbulent water and are of special concern to sailors because they can be quite hard to get around. Think back to the warm-up activity of this section. You may have drawn a route from Portugal to India that included going around the southern end of Africa. This swirling eddy of water there was a major obstacle to early explorers from western Europe trying to get around Africa toward the east.
Click on the image above to watch Ocean Surface Temperature
The Coriolis Effect
Because of the Coriolis effect, surface currents in the ocean are deflected much like air masses in the atmosphere. The Coriolis effect results in five major ocean gyres, or patterns of surface water flow, and they are shown here. Water flows clockwise in the north and counterclockwise in the south.
Question for Thought
