Atlantic-Pacific Gradients Drive Last Millennium Hydroclimate Variability in Mesoamerica

The paleoclimatic record from Mexico and Central America, or Mesoamerica, documents dramatic swings in hydroclimate over the past few millennia. However, the dynamics underlying these past changes remain obscure. We use proxy indicators of hydroclimate to show that last millennium hydroclimate variability was dominated by opposite-signed moisture anomalies in northern and southern Mesoamerica. This pattern results from changes in moisture convergence driven by Atlantic-Pacific interbasin temperature gradients. While this pattern is reproduced by several models and multiple experiments with a single model, models appear to disagree about the underlying dynamics of this interbasin gradient. Moreover, disagreement about the interbasin gradient, and associated hydroclimate pattern, dominates spread in 21st century regional hydroclimate projections. These results emphasize the role of interbasin asymmetries in governing past and future regional climate change. They also demonstrate that paleoclimate studies can elucidate mechanisms directly relevant to projecting future hydroclimate in climate change hot spots like Mesoamerica.