Influence of Andean uplift on climate and paleoaltimetry estimates

Recent elevation reconstructions of the Andean Plateau suggest a rapid 2.5 +/- 1.0 km rise of the central Andes between similar to 10 and 6 Ma. This rapid rise has been attributed to a catastrophic removal of a dense lithospheric mantle root beneath the Andes. However, these findings are based on the assumption that climate did not change during deposition of paleoaltimetry proxies. Here we evaluate South American climate change due to Andean uplift and its influence on interpretations of plateau elevation from climate-sensitive paleoaltimetry data. A series of experiments are presented using the RegCM3 regional general circulation model (RCM) to characterize changes in Andean precipitation amount, surface temperature, and wind direction (vapor source) as a function of changing plateau elevation. Results indicate that South American and Andean climate changed significantly in response to plateau growth. More specifically, rising of the plateau results in up to a 900 mm increase in rainy season (December-January-February) precipitation over the plateau. Plateau uplift also results in a decrease in non-adiabatic surface temperature of up to 6.5 degrees C (in addition to adiabatic cooling directly related to elevation change through the lapse rate). Finally, the prevailing wind direction and the vapor source for precipitation switches from the South Pacific Ocean to the equatorial Atlantic as plateau elevation increases above 1/2-3/4 of its present-day elevation. Taken together, these changes in paleoclimate would have substantially depleted the oxygen isotopic concentration of paleoprecipitation through the Cenozoic. Unless this climatic effect is taken into consideration, paleoaltimetry reconstructions based on stable isotope methods may overestimate the rapid rise of the Andes by up to several kilometers. We conclude that some or all of the apparent rapid rise of the Andean Plateau from paleoaltimetry data could be an artifact of large changes in paleoclimate. (c) 2009 Elsevier B.V. All rights reserved.