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The Honolulu Advertiser

Posted on: Monday, February 14, 2005

Corals tell of climate changes

By Jan TenBruggencate
Advertiser Science Writer

Researchers are collecting corals from ancient Hawai'i reefs to help determine what was going on in the world's climate thousands and millions of years ago.

"Corals are like trees. They lay down distinctive summer and winter bands," said Jody Webster, a geologist with the Monterey Bay Aquarium Research Institute. Webster was in Hawai'i last week for an American Geophysical Union conference entitled, "Tropical-Extratropical Climatic Teleconnections: A Long-Term Perspective," which was hosted by the University of Hawai'i's International Pacific Research Center.

Researchers are able to determine the age of coral bands by complex dating techniques that involve natural radioactive materials taken up by the corals, which decay at a known rate. By studying other components of the coral rings, scientists can determine things about the condition of the environment at the time those rings were created.

Conditions like the temperature of the ocean and the salinity — and perhaps much more — can be estimated based on the corals. Webster has studied corals from off the Big Island that are a few thousand years old and ones from off Ni'ihau that are 5 million to 6 million years old, as well as lots in between.

Webster said he and fellow scientists have been at the Hawai'i coral work only about two years, but they've found some interesting things. For instance, there was a distinctive cool period in Hawaiian waters about 8,100 years ago.

There was another, smaller cool event about 1,700 years ago. That fits the range of time estimates within which the first humans may have been arriving in the Hawaiian archipelago.

"That correlates with a cool period seen in other parts of the world," he said.

The scientists are just starting work on a fascinating period 4 million to 5 million years ago when carbon dioxide levels in the atmosphere were a little higher than they are now and temperatures were a little warmer.

"It's where we're going," he said, and suggested that studying corals from that period could shed light on what the climate will be like as the planet warms.

Webster said he hopes to determine, for instance, whether El Niņo events occurred in the mid-Pacific back then and whether they were more powerful or more frequent than they are now. Knowing that could help predict what will happen in the next few decades.

If you have a question or concern about the Hawai'i environment, contact Jan TenBruggencate, The Advertiser's Kaua'i Bureau chief and science and environment writer, at jant@honoluluadvertiser.com, (808) 245-3074 or P.O. Box 524, Lihu'e, HI 96766.