Fossil pollen records indicate that Patagonian desertification was not solely a consequence of Andean uplift

Abstract

The Patagonian steppe - a massive rain-shadow on the lee side of the southern Andes - is assumed to have evolved ∼15-12ǎ €‰Myr as a consequence of the southern Andean uplift. However, fossil evidence supporting this assumption is limited. Here we quantitatively estimate climatic conditions and plant richness for the interval ∼10-6ǎ €‰Myr based on the study and bioclimatic analysis of terrestrially derived spore-pollen assemblages preserved in well-constrained Patagonian marine deposits. Our analyses indicate a mesothermal climate, with mean temperatures of the coldest quarter between 11.4ǎ €‰°C and 16.9ǎ €‰°C (presently ∼3.5ǎ €‰°C) and annual precipitation rarely below 661ǎ €‰mm (presently ∼200ǎ €‰mm). Rarefied richness reveals a significantly more diverse flora during the late Miocene than today at the same latitude but comparable with that approximately 2,000ǎ €‰km further northeast at mid-latitudes on the Brazilian coast. We infer that the Patagonian desertification was not solely a consequence of the Andean uplift as previously insinuated.© 2014 Macmillan Publishers Limited. All rights reserved.