AD 550–600 Collapse at Teotihuacan

We analyze a 2400-year rainfall reconstruction from an ultra-high-resolution absolutely-dated stalagmite (JX-6) from southwestern Mexico (Lachniet et al., 2012). Oxygen isotope variations correlate strongly to rainfall amount in the Mexico City area since 1870 CE, and for the wider southwestern Mexico region since 1948, allowing us to quantitatively reconstruct rainfall variability for the Basin of Mexico and Sierra Madre del Sur for the past 2400 years. Because oxygen isotopes integrate rainfall variations over broad geographic regions, our data suggest substantial variations in Mesoamerican monsoon strength over the past two millennia. As a result of low age uncertainties (≤ 11 yr), our stalagmite paleoclimate reconstruction allows us to place robust ages on past rainfall variations with a resolution an order of magnitude more precise than archeological dates associated with societal change. We relate our new rainfall reconstruction to the sequence of events at Teotihuacan (Millon, 1967; Cowgill, 2015a) and to other pre-Colombian civilizations in Mesoamerica. We observe a centuries long drying trend that culminated in peak drought conditions in ca. 750 CE related to a weakening monsoon, which may have been a stressor on Mesoamerican societies. Teotihuacan is an ideal location to test for links between climate change and society, because it was located in a semi-arid highland valley with limited permanent water sources, which relied upon spring fed irrigation to ensure a reliable maize harvest (Sanders, 1977). The city of Teotihuacan was one of the largest Mesoamerican cities, which apparently reached population sizes of 80,000 to 100,000 inhabitants by AD 300 (Cowgill, 1997; 2015a). Following the “Great Fire”, which dates approximately to AD 550, population decreased to lower levels and many buildings were abandoned (Cowgill, 2015). Because of the apparent reliance on rainwater capture (Linn é, 2003) and spring-fed agriculture in the Teotihuacan valley to ensure food security and drinking water, food production and domestic water supplies should have been sensitive to rainfall variations that recharge the surficial aquifer that sustained spring discharge prior recent groundwater extraction.