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New analysis of sediment samples from the southern Caribbean indicate that severe droughts occurred at the same time as the known collapse of the Mayan civilization. In a study in the March 14 issue of the journal Science, lead author Gerald Haug of Geoforschungszentrum (GFZ) in Potsdam, Germany, together with Konrad Hughen of the Woods Hole Oceanographic Institution and colleagues report that sediments from the Cariaco Basin in northern Venezuela clearly show a dry spell across the Caribbean region starting in the seventh century and lasting for more than 200 years.

The study looked at titanium concentration in undisturbed sediments recovered by the Ocean Drilling Program. Titanium varies with input from rivers and rainfall patterns over northern tropical South America, with titanium decreasing with decreasing rainfall. The international team focused on sediments from 750 AD to 950 AD, the period when the Classic Maya civilization collapsed in the lowlands of the Yucatan Peninsula. The data show a clear link between the chronology of regional droughts and the demise of the culture.

Multi-year droughts in the region occurred at approximately 810, 860 and 910 AD and are believed to have placed enough strain on resources in the region to contribute to the demise of the civilization. The Maya flourished for about 1,000 years and had a peak population of more than one million. They built pyramids and elaborate cities with irrigation systems on the Yucatan, now part of Mexico. They depended on a seasonally consistent rainfall to support agriculture. Although some cities were repopulated at various times, many of the cities were abandoned in the 9th century AD.

"The resolution of many paleoclimate records has limited us in the past from documenting a clear link between climate change and the detailed, often complex evolution of some of the great cultures around the world.," Hughen says. "Evidence of long periods of drought had been found previously in sediments from lakes in Guatemala, but the resolution was not sufficient to identify the three phases of abandonment known from historical data. Our records have annual resolution so we can measure both the timing and the durations of the drought periods that caused each incremental collapse."

How this once great civilization collapsed has been the subject of continued debate. Paleoclimatologists have developed an increasingly accurate record of climate change for the past few thousand years, covering the same period in which human societies developed and flourished. Until recently, archaeologists and historians lacked information on short-term climate change, but now high-resolution records from ice cores, tree rings and some deep sea sediments provide evidence that climate shifts often coincided with sudden changes in human history.

Hughen, an assistant scientist in the Institution's Department of Marine Chemistry and Geochemistry, said the sediment records show a dry period beginning about 1,200 years ago that was punctuated by periods of three to nine years each when there was little or no rainfall. Each event placed more stress on the civilization, leading to a collapse of a portion of the population each time. The remaining population could not survive the last severe drought at about 910 AD.

Archeological data show that the Mayan communities in the southern and central lowlands collapsed first, while those in the northern highlands lasted for another century or so, possibly because they had access to more ground water resources. In the end, however, they couldn't survive the final dry period.

The study was conducted by Gerald Haug of Eidgenossiche Technische Hochschule (ETH) in Zürich, Switzerland, who is currently at Geoforschungszentrum (GFZ) in Potsdam, Germany, Detlef Gunther of ETH in Zürich, Switzerland, Larry Peterson of the University of Miami, Daniel Sigman of Princeton University, Konrad Hughen of Woods Hole Oceanographic Institution, and Beat Aeschlimann of ETH in Switzerland. Their work was supported by the Schweizer Nationalfonds (SNF) in Switzerland, the US National Science Foundation (NSF), and by British Petroleum and Ford Motor Company through the Princeton Carbon Mitigation Initiative.

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