Upwelling Case Study – Background Information

Making Connections Between Upwelling and El Niño

Normally, strong trade winds blow from the east along the equator, pushing warm water westward. This induces upwelling off the coast of South America. (Click on diagram at left to enlarge.)

During El Niño, however, weakened trade winds allow warm water to flow toward South America. This prevents the nutrient-carrying cold water from upwelling and disrupts the food web off South America. (Click on diagram at right to enlarge.)

Away from the equator — including Monterey, California — the relationship between wind direction and coastal upwelling becomes more complicated but no less important for fisheries. Although currents in the upper ocean are driven by winds, they are also deflected away from the wind direction by the earth’s rotation. The tendency of moving objects to deflect in a rotating reference frame is called the Coriolis effect. Earth’s rotation causes ocean currents to deflect to the right in the northern hemisphere and to the left in the southern hemisphere. Which wind direction leads to upwelling in the northern hemisphere (e.g., California)? Southern hemisphere (e.g., Peru)?

Wind-driven upwelling brings cool, nutrient-rich water to the Monterey Bay Sanctuary, which spans hundreds of kilometers of California’s coastline. Because upwelling varies in time and intensity,MBARI scientists have deployed two moorings in Monterey Bay. (Click on diagram to enlarge.)

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Upwelling Case Study


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