Mapping Change with Mollusks. (iOjo!)

Article excerpt

IN THE PAST DECADE the weather phenomenon known as El Nino has dramatically affected the Americas--causing the loss of lives, crop destruction, and devastation of fishing industries. To better understand this weather event, researchers are studying the history of El Nino and how it may have affected ancient Societies. Because northern Peru is a core region of El Nino activity, Associate Professor Dan Sandweiss of the University of Maine Department of Anthropology and Institute for Quaternary and Climate Studies is using mollusks from archaeological sites on the coast of Peru to shed light on the history of El Nino. His research has been able to determine the frequency of El Nino events thousands of years ago and how these weather patterns affected the rise and fall of early Peruvian societies.

"El Nino was absent or incredibly rare until about fifty-eight hundred years ago," Sandweiss says. "We found that there were changes in the frequency of El Nino events about fifty-eight hundred and three thousand years ago and that they correlate in time with cultural change."

For the past twenty years, Sandweiss has been studying ancient mollusk and fish remains. Because mollusks are sensitive to temperature shifts, they tell the story of climate changes throughout history. Sandweiss has combined his research that tells when and where specific groups of mollusks lived and died with the knowledge of the temperatures they live and die at, to construct a climate record of the ancient Peruvian coast.

He discovered that two species--Mesodesma donacium and Choromytilus chorus--were found in coastal Peruvian archaeological sites until about three thousand years ago. Both species are very sensitive to the uncharacteristically warm water an El Nino brings. "The rapid disappearance of these species from northern Peruvian archaeological sites probably reflects an increase in the frequency of strong El Nino events," Sandweiss wrote in the July 2001 issue of Geology. …