THURSDAY, JULY 12,
2001
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By
Laurent Belsie (belsiel@csps.com)
SAN DIEGO
Move over, El Niño.
Using coral from a tiny Pacific atoll, researchers have discovered a new tropical ocean temperature swing with worldwide implications, from droughts in Brazil to monsoons in India.
The finding suggests that temperature swings in the Pacific with time scales longer than El Niño affect regional climates. The existence of such cycles could potentially improve scientists' ability to make long-range climate forecasts with far more confidence than they do today.
The new research shows that over the past 112 years, surface-water temperatures in the tropical Pacific have fluctuated every 12 to 13 years. This cycle correlates closely to similar cycles previously documented in the Atlantic and Indian oceans and may, in fact, cause them. "This provides convincing evidence that these three ocean basins are linked on time scales beyond El Niño, which is intriguing," says Kim Cobb, lead author of the new study from the Scripps Institution of Oceanography here at the University of California, San Diego.
The new cycle doesn't carry the punch of El Niño, which can change ocean temperatures by as much as 6 degrees C (43 degrees F.). But it may be far more predictable than El Niño, whose cycle varies anywhere from two to seven years. And their geographic footprints share many similarities.
Thus, just as El Niño triggers events worldwide, the newly discovered Pacific cycle may set off Atlantic and Indian Ocean phenomena.
Temperatures of the tropical Pacific have always proved difficult to catalog because instrumental records were so scarce.
But Ms. Cobb, a graduate student, along with her colleague, Christopher Charles, found rich deposits of coral on the tiny atoll of Palmyra, some 1,000 miles south-southwest of Hawaii.
They drilled samples from more than 70 of the coral heads to gather their climate records. She dated the samples and, comparing tiny differences in their ratio of oxygen isotopes, measured remarkably precise month-to-month changes in the seawater temperatures.
The living Palmyra coral dates back to around AD 1886. Cobb is using fossilized coral samples to construct a longer record.
According to a preliminary look at that data, it appears that El Niño operated fairly normally during both a warm period around AD 1000 and Europe's cold spell near AD 1700.
"The El Niño system doesn't seem to care what was happening," Cobb says. Perhaps "we don't need to be concerned about El Niño characteristics changing over the next 50 years. But that's highly speculative and controversial at this time." Cobb plans to finish her study this fall.
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