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Columns::March 4, 2002
Former U.N. commissioner wins Delta Prize for Global Understanding
Office of Institutional Diversity holds open house
Setting priorities: Annual management conference focuses on budget, partnerships
McBee, emeritus vice president, will receive state humanities award
Limited hiring freeze goes into effect
Campus Closeup
Head of food services department wins Silver Plate Award
Kudos
Visions of Middle-earth
Workshop for two-year colleges
UGA vs. Oxford Union
Campus News
There are bones about it
By Phil Williams
phil@franklin.uga.edu
New evidence from two Peruvian archeological sites--excavated by researchers from the University of Maine and analyzed by
UGA scientists--supports the theory that a climate shift about 5,000 years ago led to modern weather patterns that include El Niño. The details were presented in an article in the journal Science in February.
The lead author of the article is C. Fred Andrus, a postdoctoral associate in UGA’s geology department. Co-authors include UGA faculty members Douglas E. Crowe (geology), Elizabeth J. Reitz (Georgia Museum of Natural History) and Christopher S. Romanek (Savannah River Ecology Laboratory) and Daniel H. Sandweiss of the University of Maine. The paper presents the results of chemical analyses of fish bones known as otoliths from a species of sea catfish living along the Peruvian coast.
“Our data strengthens the argument that El Niño, as we know it, began relatively recently--since 5,000 years ago,” says Andrus. (El Niño is, in large part, warming of the ocean waters off Peru at irregular intervals.) “This is more evidence that climate change is the norm, and climate stability is the exception in the earth’s history, even in relatively recent times.”
Andrus says that otoliths from sea catfish are a good candidate for this kind of analysis because the fish do not migrate. They tend to stay near shore in relatively small areas away from river mouths where fresh water can complicate the oxygen results.
“Otoliths act like miniature temperature-recording devices,” says Crowe. “Throughout the life of a fish, they grow concentrically larger, and the ratio of oxygen isotopes in each individual growth band allows us to determine the temperature of the water at that time. By looking at the entire otolith, we can reconstruct the water temperature history throughout the life of the fish, from season to season and year to year.”
In 1996, Sandweiss, Reitz and three other scientists co-authored a paper in Science presenting new evidence of conditions indicating the onset of El Niño about 5,000 years ago. Their conclusions were based on the identification of mollusk and fish remains from archaeological sites. Some critics of that paper suggested that the mollusks might have lived in warm water embayments that would not accurately reflect temperatures in the open ocean.
“The evidence in this paper, based on fish that live off shore, strongly supports the conclusions that we reached in 1996,” says Sandweiss.
The current paper in Science is allied to two other papers by Andrus and Crowe, now in press at the Journal of Archaeological Sciences and the journal Paleoceanography. The JAS paper shows that cooking and subsequent burial for 5,000 to 8,000 years didn’t alter the oxygen isotope signatures. The research to be published soon in Paleoceanography establishes the use of otoliths as proxies for temperature, using modern fish to show the technique works. The new Science paper, in a sense, brings this research together.
Andrus has participated in archaeological studies led by Sandweiss in Peru, analyzing oxygen isotopes on otoliths from modern fish as well as from seven sea catfish otoliths from the archaeological site at Ostra in 1991 and five from the site at Siches in 1995. Siches is located in far northern Peru, near the border with Ecuador; Ostra is about midway between Siches and Lima. The results at Ostra showed that, prior to 5,000 years ago, winter water temperatures were similar to those of today but summer temperatures were much warmer. Thus, the average annual temperature was about three degrees Celsius warmer than at present. At Siches, although there was little seasonal variation, temperatures were also about three to four degrees warmer than they are today.
“A change in El Niño frequency and the related increase in upwelling about 5,000 years ago may be related to changes in fishing resources and increased cultural complexity,” says Reitz. Sandweiss and his colleagues published a paper in Geology in 2001 suggesting that cultural changes such as the construction of cities and large monuments may have been related to the onset of El Niño 5,000 years ago and later to changes in its frequency and intensity.
“Our research shows that the current El Niño cycle is significantly different from what it was 5,000 to 8,000 years ago,” says Andrus. “Our hope is that our data can be used to build accurate predictive models of future El Niño events.”
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