Santa Cruz, Calif. - After nine weeks in the Bering Sea on a research vessel, University of California-Santa Cruz professor Christina Ravelo and a team of scientists came back with sediment samples from below the sea floor that will help illuminate the Pliocene epoch, the last major warm period in Earth's history.

Preliminary analysis of the sediment cores, which Ravelo presented to a meeting of the American Geophysical Union in San Francisco earlier this month, indicates that the region was ice-free all year and that there was a high level of biological activity. Today, the Bering sea is only ice-free during the summer.

Scientists are interested in the period for what it may reveal about the effects of global warming.

Data from near the Arctic is especially pertinent, because current research shows temperatures are rising more rapidly around the Arctic than other places on Earth.

The Pliocene epoch started roughly 5 million years ago, and includes the last warm period before a series of ice ages. Analysis of the sediment showed that, while average global temperatures were about three degrees Celsius higher than today in most places, temperatures at the Bering Sea were at least 5 degrees warmer than today.

Ravelo and other scientists will now spend the next few years studying the samples and refining their conclusions.

"First we try and get a broad-brush view of what was going on, then we do more detailed analysis," said Ravelo, who has been at UC-Santa Cruz since 1992. "We do things at higher resolution, at a finer spatial and temporal scale. ... Also, the material is archived so it is open to other researchers that want samples."

Ravelo and co-chief scientist Kozo Takahashi of Japan's Kyushu University led the expedition to the Bering Sea this past summer as part of the Integrated Ocean Drilling Program.

The ship Ravelo was on, JOIDES Resolution, is the only U.S. ship that can do the type of drilling needed for this work. The deepest sediment samples were taken from 700 meters below the sea floor, and took several days to complete.

"It's an amazing ship," Ravelo said. "It can go out for two months and be completely independent from anything on shore. ... It's a 24 hours a day, seven days a week operation. The ship uses a dynamic positioning system which keeps the ship on target. You wait for the drill to hit the target depth and then move and do another one. It's a really unique operation."

The research also shows that the amount of sea ice in the region was much more variable than previously thought.

"Being able to detect changes in sea ice distribution was one of the most rewarding results," Ravelo said. "The role of sea ice in climate change is not understood very well. ... The fact that sea ice variations came and went so dramatically was surprising."

The Integrated Ocean Drilling Program is supported by the European Union, Japan and the United States, through the National Science Foundation. The program will end in 2013, and planning is underway for the next phase of ocean drilling.

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(c) 2010, Santa Cruz Sentinel (Santa Cruz, Calif.).

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AP-WF-01-01-11 0157GMT