Thursday, July 17, 2003
New Pacific Ocean Record Gives Fresh Insight Into Recent Climate Warming, El Niño Patterns
Scripps researchers use coral fossils to track climate change over the last millennium Images available upon request.
Scripps Institution of Oceanography / University of California, San DiegoBy stitching together valuable sea temperature information from an obscure Pacific Ocean island, researchers at Scripps Institution of Oceanography at the University of California, San Diego, have constructed an important new record of climate change over the last 1,100 years.
Using coral fossils from tiny Palmyra atoll, a remote central Pacific island, and several laboratory analysis techniques, Kim Cobb and Christopher Charles developed a unique window into climate variability over the last millennium. Their results are published in the July 17 issue of the journal Nature.
Among its most striking revelations, the fossil-coral record shows a clear trend of increasingly warmer and wetter climate in the central tropical Pacific in the late 20th century, particularly since 1976, a change unprecedented in the last millennium. The record also depicts a range of new information about the El Niño phenomenon, including the first glimpses of El Niños in the 17th century that matched or exceeded recent powerful El Niños in the 1980s and 1990s.
"The first thing that leapt out at us was the trend towards a warmer, wetter climate in the 20th century," said Cobb, who received a doctoral degree from Scripps Institution last year. "You don't need a microscope to see the dramatic changes in recent decades."
Charles, an associate professor in the Geosciences Research Division at Scripps, says the records are the first direct evidence for the behavior of El Niño in the pre-industrial period. He believes the results will be important for future studies investigating
human activities and their influence on El Niño events. Some have speculated that El Niños have become stronger as a result of such activities.
"To the contrary," said Charles. "These results show that there were episodes during the height of the little ice age when El Niño was just as strong, if not stronger, than the 1997 and 1982 El Niño events. The study also found episodes when El Niño activity jumped abruptly from one regime to another-a strong suggestion that El Niño is essentially a chaotic phenomenon, as opposed to one that responds regularly to some external forcing."
The coral-fossil record indicates wide fluctuations of El Niño activity, revealing the most intense events during the mid-17th century. More than five years ago, Cobb and Charles identified Palmyra and other parts of the Pacific's Long Island chain as potential sources of new climate change information. In 1998 and 2000, Cobb led expeditions there and used portable drills to extract well-preserved core samples from a variety of coral heads above and below sea level.
Laboratory analyses, including mass spectrometry and uranium and thorium geochemistry, were used to determine precise sea surface temperature and climate fluctuations at the atoll. These were carefully spliced together month by month over several centuries of the last 1,100 years.
"This study provides one of the most direct reconstructions of tropical Pacific climate over the last millennium," said Cobb, currently a post-doctoral researcher at the California Institute of Technology in Pasadena, Calif. "Such data from the tropical oceans never existed so it gives us a new baseline of where we have been and where we might be going."
The clear warming trend seen during the late 20th century, the paper notes, in all probability relates to the rise in greenhouse gases. The paper concludes that the Palmyra
corals could provide critical tests of climate models charged with predicting future
Coauthors of the study were Hai Cheng and R. Lawrence Edwards of the University of Minnesota.
The research was supported by the Khaled bin Sultan Living Ocean Foundation, the Nature Conservancy, the National Science Foundation, and the National Oceanic and Atmospheric Administration.
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Scripps Institution of Oceanography at the University of California, San Diego, is one of the oldest, largest, and most important centers for global science research and graduate training in the world. The scientific scope of the institution has grown since its founding in 1903. A century of Scripps science has had an invaluable impact on oceanography, on understanding of the earth, and on society. More than 300 research programs are under way today in a wide range of scientific areas. Scripps operates one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration. Now plunging boldly into the 21st century, Scripps is celebrating its centennial in 2003.
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Scripps Institution of Oceanography, at University of California, San Diego, is one of the oldest, largest and most important centers for global science research and education in the world. The National Research Council has ranked Scripps first in faculty quality among oceanography programs nationwide Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today in 65 countries. The institution has a staff of about 1,300, and annual expenditures of approximately $155 million from federal, state and private sources. Scripps operates one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration.
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