Onset of Convective Rainfall During Gradual Late Miocene Rise of the Central Andes

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Science  01 Apr 2010:
DOI: 10.1126/science.1185078


A decrease in sedimentary carbonate δ18O from the Bolivian Altiplano has been interpreted to indicate rapid late Miocene Andean plateau (AP) surface uplift. Here, we report on paleoclimate simulations of Andean surface uplift with an atmospheric general circulation model (GCM) that tracks oxygen isotopes in vapor. The GCM predicts changes in atmospheric circulation and rainfall that influence AP isotopic source and amount effects. On eastern AP slopes, summer convective precipitation increases by up to 6 mm day-1 (>500%) for plateau elevations >~2000 m. High precipitation rates enhance the isotope amount effect, leading to a decrease in precipitation δ18O at high elevations and an increase in δ18O lapse rate. Our results indicate that late Miocene δ18O depletion reflects initiation and intensification of convective rainfall.