UC Berkeley

Proxy records from the last millennium in Mesoamerica suggest a widespread interval of drought at some point between the 7th and 13th centuries CE. In some records, this time period represents the driest proxy values in the last few millennia. There is currently no clear dynamical explanation for these droughts, nor consensus as to whether they were spatiotemporally coherent over the region. We perform several analyses to develop a novel hypothesis to explain these droughts that is consistent with our knowledge of the dynamics of the climate system. We use Bayesian age modeling techniques and a synthesis of regional proxy records to suggest that there is robust evidence of drying between 800 and 1050 CE, with the sites showing dry conditions clustered in southern central America. By studying control simulations of two general circulation models (GCMs), we suggest that this pattern may be diagnostic of hydroclimate changes associated with multidecadal variability in the Atlantic Basin. Models and instrumental data suggest that cooling of tropical Atlantic SSTs and strengthening of the North Atlantic Subtropical High drives a pattern of multidecadal drought with negative rainfall anomalies in southern central America and positive anomalies in northern Mexico. This process could have resulted in the droughts observed in the proxy record. Our work offers a novel hypothesis about the dynamics of multidecadal drought in Mesoamerica, and builds on previous efforts to synthesize proxy records from the region.