Coral Cores Reveal Secrets Of El Nino

Credit: Georgia Tech Photo: Jordan Watson
Credit: Georgia Tech Photo: Jordan Watson

By examining a set of fossil corals that are as much as 7,000 years old, scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a Pacific Ocean climate cycle that affects climate worldwide.

Showing that 20th century ENSO climate cycles are significantly stronger than ENSO variations captured in the fossil corals the new coral data nevertheless reveals large natural variations in past ENSO strength, making it difficult to attribute the 20th century intensification of ENSO to rising carbon dioxide levels.

By analyzing the ratio of specific oxygen isotopes in the coral skeletons, the scientists obtained information about ENSO-related temperature and rainfall variations during the periods of time in which the corals grew. The isotope ratio of the coral skeleton changes with the temperature and amount of rainfall, providing detailed information about environmental conditions during each period of the coral’s growth.

Using the new sequences to quantify the range of natural variability in ENSO strength, the researchers have detected a modest, but statistically-significant increase in 20th century ENSO strength that may be related to climate change.

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