How do trade winds cause upwelling

In winter, winds blow from the south to the north, resulting in downwelling. During the summer, winds blow from the north to the south, and water moves offshore, resulting in upwelling along the coast. This summer upwelling produces cold coastal waters in the San Francisco area, contributing to the frequent summer fogs. Duxbury, et al, Upwelling occurs where surface currents are diverging, or moving away from each other. As the surface waters diverge, deeper water must be brought to the surface to replace it, creating upwelling zones.

The upwelled water is cold and rich in nutrients, leading to high productivity. Many of the most productive regions on Earth are found in upwelling zones. In the equatorial Pacific, the trade winds blow the North and South Equatorial Currents towards the west, while Ekman transport causes the upper layers to move to the north and south in their respective hemispheres.

This creates a divergence zone, and a region of upwelling and high productivity Figure 9. A similar process occurs near the Antarctic continent, creating one of the most productive regions on Earth, the Antarctic divergence. With both currents occurring in the Southern Hemisphere, Ekman transport will be to the left, so the eastward-flowing West Wind Drift water will be transported to the north, and the westward-flowing East Wind Drift water will be transported to the south, creating a highly productive divergence zone Figure 9.

Ekman transport and the Coriolis Effect make the coastal waters move, on average, 90 degrees to the wind. This means the water near the coast is being pushed west, away from the coast. This, in turn, pulls deep water up to the surface to replace the original surface water. Horizontal movements are referred to as currents, while vertical changes are called upwellings or downwellings.

Explore how ocean currents are interconnected with other systems with these resources. The ocean is in constant motion, transporting nutrients through its layers and around the globe. A body of surface water can persist all year long or for only part of the year.

Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Upwelling usually results in rich fisheries. Photograph by Bates Littlehales. Coriolis effect. Northern Hemisphere. Southern Hemisphere. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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