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Paleo Slide Set: Coral Paleoclimatology:Natural Record of Climate change for High School Student
South Pacific cross-section during El Niņo years.
During El Niño years, the trade winds weaken. Warm water is no longer pushed westward and cold nutrient-rich water is no longer upwelled to the surface along the South American coast. Interestingly, because there is more rainfall in the interior of Peru (a normally dry region) during an El Niño, the local agricultural industry fares well. However, fish catches decline markedly during these warm periods, producing economic hardships not only for individual fishermen, but also for entire nations such as Chile and Peru.

El Niño is a natural event that has been occurring for thousands of years, so Peruvians should expect its arrival. Unfortunately, no one knows exactly when the next El Niño will occur, how intense it will be, or how long it will last. We only know that the average occurrence is every 3-7 years and it lasts for an average of 1-2 years. Scientists are working to find ways to better predict when the next El Niño will come and how strong it will be. Buoys are set up along the equator of the central Pacific to take records of the sea surface temperatures (SSTs), wind speeds and barometric pressures. When the winds slow down an El Niño is on its way.

Scientists can also detect the past occurrences of El Niño by looking at the past sea-surface changes in corals. El Niño affects the growth and chemistry of the coral bands. Isotopes of oxygen locked in the coral skeleton record past water temperatures and can indicate an El Niño. The information recorded in the coral bands can tell us more about the frequency and duration of El Niños.

During the strongest ENSO of the century in 1982-83, the temperatures in the western Pacific increased by up to 5 degrees Celsius. The stress due to warmer than normal temperatures caused some of the coral polyps to bleach. Although bleaching after El Niño is normal, the amount of coral bleaching seems to be on the rise, and El Niño appears now to be affecting areas that have not been affected in the recent past.

Photo Credits:
Sarah H. Dawson
NOAA Paleoclimatology Program

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Last Modified: 12 October 2001

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