Late Miocene-early Pliocene hydroclimate evolution of the western Altiplano, northern Chile: Implications for aridification trends under warming climate conditions

The Miocene-Pliocene boundary (∼5.3 million years ago, Ma) represents a climate transition, where global warming resulted in a rise in sea surface temperatures from near modern values in the late Miocene, to sustained, warmer than modern values in the early Pliocene. Estimated atmospheric CO2 concentrations were within the range of anthropogenic values. Thus, this transition provides an opportunity to evaluate hydroclimate responses to warming, when the Earth system was in equilibrium with near modern atmospheric CO2 levels. Here, we utilize lacustrine carbonate stable and clumped isotope methods, and palynology, to investigate hydroclimate trends within the western Altiplano of Chile during the late Miocene and early Pliocene. The results provide observational support for a warmer and wetter-than-modern climate over these timeframes. However, increasing aridity across the Miocene-Pliocene boundary suggests a hydroclimate response to global climate forcing. Given the sensitivity of the region's climate to disturbances in tropical Pacific, ocean-atmospheric processes, we speculate that this aridification may reflect progressive weakening of the Pacific Walker Circulation, in response to global warming.