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Sea coral offers climate clues for UA researchers

An old myth says if a man puts a sea shell to his ear, he can hear the ocean.

While that is not true, scientists are now listening to what sea coral have to say.

Using annual growth rings from sea coral found off the coast of Africa, a UA scientist and three colleagues from Kenya and California have reconstructed ocean climate variations of the western Indian Ocean.

University of Arizona geosciences assistant professor Julia Cole and her team - Rob Dunbar, Tim McClanahan, and Nyawira Muthiga - were able to reproduce climate histories dating back to the early 1800s.

When ocean temperatures rise, sea coral embody less oxygen into their annual rings than during cooler times.

"In this study, we used a coral that has exceptionally clear annual banding, and we developed the climate story using a geochemical measurement of the different isotopes of oxygen in the coral skeleton," Cole stated in an e-mail interview.

Using this information, the team of researchers examined the coral's growth rings and found the western Indian Ocean warms and cools on a 10-year cycle, which is linked to El NiÛo.

A small section of a 12-foot tall sea coral, located about 20 feet underwater, helped Cole's team create a temperature scale to coincide with varying amounts of oxygen molecules in sea coral skeletons.

Cole added that because of advancements in technology during the 1980s, scientists found that "corals incorporate oxygen from sea water into the skeletons they build out of calcium carbonate."

Cole said she is satisfied with results gathered from the sea coral off the Kenyan coast because another analysis done on a coral from the Seychelles, located about 900 miles away, yielded similar results.

She added that these results are important because "people often question whether recent increases in temperature are natural or caused by human activity."

"Our record shows that at this site, the warm temperatures of the past decade are definitely unusual in the context of the past 200 years," Cole said.

UA atmospheric physics research assistant professor Andrea Hahmann said it is important to know about past climate patterns.

"Our observed data doesn't go very far back," she said. "Also, we need to know about past climate patterns to determine whether changes in climate are natural or human caused."

Hahmann also pointed out there are few data stations in places like Australia, making the sea coral research all the more important.

Cole said the coast off of Kenya was a prime place for sea coral research because of the major impacts El NiÛo storms have had on the region in recent years.

"We first started in this region because we knew that ocean conditions there play a role in regional rainfall patterns," she said. "We also knew that the area was sensitive to El NiÛo fluctuations."

El NiÛo has greatly affected the people of Kenya, but the phenomenon impacts other parts of the world as well.

"Different areas of the world respond differently to El NiÛo. The challenge for us is to choose the right areas to examine for El NiÛo-related anomalies, and to choose the right techniques to expose those anomalies," Cole said.

"Corals everywhere record the local environmental conditions, but only corals in regions sensitive to El NiÛo would be able to give the kind of information we determined from this analysis," she said.