Making Connections Between Upwelling and El Niño
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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 to enlarge.) |
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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 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. Roll your cursor over the diagram of a western coastline to see how upwelling is tied to alongshore winds. 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.)
Additional Resources:
- Is upwelling always good for marine life? Learn how upwelling can be a "mixed blessing to coastal ecosystems" from NOAA Ocean Explorations: Sanctuary Quest
- Sanctuary Integrated Monitoring Network (SIMoN)
- About National Marine Sanctuaries
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Last updated: Feb. 17, 2009