Newswise — Over 400 meters of sediment core collected beneath the Arctic Ocean by an international team of scientists have revealed a 56-million-year record of climate changes that could help clarify present and future climate trends.
Results of the 2004 research expedition, led by scientists from the University of Rhode Island and Stockholm University, are reported in the June 1 issue of the journal Nature.
"Little direct evidence about the environmental history of the Arctic Ocean existed before our cruise, partly because of the enormous technological challenges of collecting the samples," said Kate Moran, professor of oceanography and ocean engineering at URI and co-chief scientist on the expedition. "Our analysis of the core sample suggests that 55 million years ago the Arctic was much warmer than today. We anticipate that our data will be used by climate modelers to give us better information about how climate change occurs and where global climate might be heading.
"Today's warming of the Arctic can, in all likelihood, be attributed to mankind's impact on the planet," she added, "but as our data suggest, natural processes operating in the past have also resulted in a significant warming and cooling of the Arctic."
The sediment cores provide a surprising Cenozoic Era record of a climate transition from a warm "greenhouse" world in the late Palaeocene and early Eocene epochs to a colder "icehouse" world influenced by sea ice and icebergs from the middle Eocene to the present.
The researchers discovered that 55 million years ago, during a period called the Palaeocene Eocene Thermal Maximum, which was similar in climate to today, the surface temperature of the Arctic Ocean was much warmer than previously believed " perhaps as much as 20 degrees Celsius higher than today. The team was also surprised to find the remains of a large quantity of freshwater ferns, dated to 49.5 million years ago, which suggests that the ocean had considerably lower salinity levels and conditions amenable to the formation of sea ice.
Pebbles and sand in the sediment cores " debris that fell out of floating ice " is evidence of climate cooling 45 million years ago, about 35 million years earlier than previously believed. The revised timing of this Arctic cooling coincides with similar events in Antarctica, supporting the belief that global climate changed symmetrically at both poles.
"One striking feature of the overall sediment record is the average sedimentation rate ranging from 1-2 centimeters per thousand years, which is an order of magnitude higher than estimates made by previous investigators who interpreted the Arctic as 'sediment-starved,'" wrote the authors.
This Arctic Coring Expedition was undertaken by the National Science Foundation-sponsored Integrated Ocean Drilling Program, an international research effort that explores the history and structure of the Earth as recorded in seafloor sediments and rocks. Because of the constantly moving sea ice in the area, the expedition used three icebreakers " two as a protective shield around the third, which served as the coring vessel.
"The drillship maintained a fixed location and cored into the seafloor while the other two vessels protected this ship by breaking up the moving sea ice and pushing the pieces away," Moran said in an interview with Nature. "This prevented the drillship from being knocked off its location. It's a technique that had never been attempted"¦and it worked wonderfully. We were able to maintain location in one drill hole for as long as nine days."
The drilling was done at four sites on the Lomonosov Ridge, approximately 1,000 meters under the sea-surface and 250 kilometers from the North Pole.
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