Increased moisture availability in the Central Andes during the Miocene Climatic Optimum

The Miocene Climatic Optimum (MCO; ∼17–14 Ma) is one of Earth's most recent protracted warming events and serves as an analog to anthropogenic climate change. Constraining the land surface response to the MCO is critical for paleoclimate model validation and for predictions of future climatic response. However, nonmarine records across the MCO interval are limited. The hinterland and foreland basins of the southern Central Andes in Argentina preserve stratigraphic records across the MCO. These continental deposits record the onset of dune fields at >30 Ma to ∼19 Ma, with widespread eolian deposition at ∼22–17 Ma. We document a regional change from eolian dune fields to fluvial and lacustrine conditions at ∼18–15 Ma, broadly coincident with the MCO, over ∼1000 km along-strike, in localities that would have occupied both high and low elevation positions and from different tectono-morphic settings. These paleoenvironmental changes are corroborated by new climate model simulations which show increased seasonality and precipitation along the eastern flank of the southern Central Andes during the MCO. Our results support a shift from arid to more humid and seasonal conditions during the MCO in the southern Central Andes, likely driven by intensification of the South American monsoon.