Prior evidence has indicated that droughts could have been key factors in the fates of major cultures in ancient Mexico and Central America (Mesoamerica). But there have been many gaps in the paleoclimate record, such as the exact timing and geographic extension of some seemingly influential dry spells.
The new, 1,238-year-long tree-ring chronology, the longest and most accurate of its kind for Mesoamerica, is the first to reconstruct the climate of pre-colonial Mexico on an annual basis for more than a millennium, pinning down four ancient megadroughts to their exact years.One large ancient drought previously confirmed for the Southwest of the United States is shown to have extended into central Mexico (1149-1167 AD) by the new dendrochronology, or tree- ring reconstruction. There it may have devastated the local maize crops, potentially giving a fatal blow to the declining Toltec culture, says David Stahle, a paleoclimatologist at the University of Arkansas at Fayetteville and lead author of the new study. Stahle and his colleagues present their new findings in a paper that has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
This far-reaching rainfall chronology also provides the first independent confirmation of the so- called Terminal Classic drought, a megadrought some anthropologists relate to the collapse of the Mayan civilization. This decades-long dry period had been previously determined by analysis of lake and basin sediments in other areas of Mexico and the Caribbean. But Stahle's team has narrowed the event's timing to 897-922 AD and confirmed that it had a wider geographical impact than previously thought, extending into the highlands of Central Mexico, where other classic period cultures were located.
"Certainly these cultural changes were very complicated -- probably not one single explanation can account for the collapse of the Mayan civilization," Stahle says. "[But] our study will allow other scientists to more thoroughly investigate and understand the impact of these droughts."
Stahle and his team used data from 74 core samples extracted from 30 specimens of millennium- old Montezuma baldcypress trees (Taxodium mucronatum) growing in the canyon of Amealco, Queretaro -- only 90 kilometers (56 miles) away from Tenochtitlan, capital of the Aztec empire, and 60 km (37 mi) northeast from Tula, the Toltec state's main city. Stahle says this tree species, related to North American sequoias, is the only plant in Central America that frequently lives up to one thousand years or more.
R. Acuna Soto: Departamento Microbiologia y Parasitologia, UNAM, Mexico, D.F., Mexico;
M.D. Therrell: Department of Geography, Southern Illinois University, Carbondale, Illinois, USA.Contact information for the author:
Maria-Jose Vinas | American Geophysical Union
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