Proceedings of the National Academy of Sciences Proc. Natl. Acad. Sci. U.S.A. 0027-8424 1091-6490 02 10 2015 112 6 Cultural implications of late Holocene climate change in the Cuenca Oriental, Mexico Tripti Bhattacharya Departments of aGeography and Roger Byrne Departments of aGeography and Harald Böhnel Centro de Geociencias, Universidad Nacional Autónoma de México, Querétaro 76230, Mexico; Kurt Wogau Centro de Geociencias, Universidad Nacional Autónoma de México, Querétaro 76230, Mexico; Ulrike Kienel Climate Dynamics and Landscape Evolution, Helmholtz Centre Potsdam, German Research Centre for Geosciences, 14473 Potsdam, Germany; and B. Lynn Ingram Departments of aGeography and Earth and Planetary Science, University of California, Berkeley, CA 94720; Susan Zimmerman Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550 Significance

Researchers have long invoked drought to explain the demise of many pre-Columbian Mesoamerican sites. However, the climatic history of many regions of Mesoamerica remains poorly understood. This includes the region around Cantona, a large fortified city in highland Mexico that was abandoned between 900 CE and 1050 CE. We used stable isotopes and elemental concentrations from lake sediments to reconstruct past climate, and found evidence of regional aridity between 500 CE and 1150 CE. In the initial phase of drought, Cantona’s population grew, possibly as a result of regional political instability. However, by 1050 CE, long-term environmental stress likely contributed to the city’s abandonment. Our work highlights the interplay of environmental and political factors in past human responses to climate change.

There is currently no consensus on the importance of climate change in Mesoamerican prehistory. Some invoke drought as a causal factor in major cultural transitions, including the abandonment of many sites at 900 CE, while others conclude that cultural factors were more important. This lack of agreement reflects the fact that the history of climate change in many regions of Mesoamerica is poorly understood. We present paleolimnological evidence suggesting that climate change was important in the abandonment of Cantona between 900 CE and 1050 CE. At its peak, Cantona was one of the largest cities in pre-Columbian Mesoamerica, with a population of 90,000 inhabitants. The site is located in the Cuenca Oriental, a semiarid basin east of Mexico City. We developed a subcentennial reconstruction of regional climate from a nearby maar lake, Aljojuca. The modern climatology of the region suggests that sediments record changes in summer monsoonal precipitation. Elemental geochemistry (X-ray fluorescence) and δ 18 O from authigenic calcite indicate a centennial-scale arid interval between 500 CE and 1150 CE, overlaid on a long-term drying trend. Comparison of this record to Cantona’s chronology suggests that both the city’s peak population and its abandonment occurred during this arid period. The human response to climate change most likely resulted from the interplay of environmental and political factors. During earlier periods of Cantona’s history, increasing aridity and political unrest may have actually increased the city’s importance. However, by 1050 CE, this extended arid period, possibly combined with regional political change, contributed to the city’s abandonment.

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