Atlantic and Pacific Ocean synergistic forcing of the Mesomerican monsoon over the last two millennia

Abstract:

We present a new replicated, high resolution (~2 yrs) and precisely-dated (± 4 yr) wet season hydroclimate reconstruction for the Mesoamerican sector of the North American Monsoon over the past 2250 years. Our new reconstruction is based on two aragonite stalagmites from southwestern Mexico which replicate oxygen isotope variations over the 950-1950 CE interval, and are calibrated to instrumental rainfall variations in the Basin of Mexico. Such data complement existing dendroclimatic reconstructions of early wet season and winter drought severity. Comparisons to indices of ocean-atmosphere circulation show a combined forcing by the North Atlantic Oscillation and the El Niño/Southern Oscillation. Monsoon strengthening coincided with synergistic forcing of a La Niña-like mode and a negative North Atlantic Oscillation, and vice versa for droughts. Although drought is commonly invoked as an stressor leading to societal change, the role of intensified monsoon onto cultural development is rarely explored. We observe that prominent transitions from drought to pluvial conditions are associated with population increases in three of the major highland Mexico civilizations of Teotihuacan, Tula Grande, and the Aztecs. These data suggest a role for ocean-atmosphere dynamics arising from the Atlantic and Pacific Oceans on Mesoamerican monsoon strength.