Understanding the patterns of rainfall isotopic composition in the central Andes is hindered by sparse observations. Despite limited observational data, stable isotope tracers have been commonly used to constrain modern-to-ancient Andean atmospheric processes, as well as to reconstruct paleoclimate and paleoaltimetry histories. Here, we present isotopic compositions of precipitation (δ 18 O p and δD p ) from 11 micrometeorological stations located throughout the Bolivian Altiplano and along its eastern flank at ~21.5°S. We collected and isotopically analyzed 293 monthly bulk precipitation samples (August 2008 to April 2013). δ 18 O p values ranged from -28.0‰to 9.6‰, with prominent seasonal cycles expressed at all stations. We observed a strong relationship between the δ 18 O p and elevation, though it varies widely in time and space. Constraints on air sourcing estimated from atmospheric back trajectory calculations indicate that continental-scale climate dynamics control the interannual variability in δ 18 O p , with upwind precipitation anomalies having the largest effect. The impact of precipitation anomalies in distant air source regions to the central Andes is in turn modulated by the Bolivian High. The importance of the Bolivian High is most clearly observed on the southern Bolivian Altiplano. However, monthly variability among Altiplano stations can exceed 10‰in δ 18 O p on the plateau and cannot be explained by elevation or source variability, indicating a nontrivial role for local scale effects on short timescales. The strong influence of atmospheric circulation on central Andean δ 18 O p requires that paleoclimate and paleoaltimetry studies consider the role of South American atmospheric paleocirculation in their interpretation of stable isotopic values as proxies.
Bibliographical noteFunding Information:
Monthly isotope and micrometeorological are available in the supporting informa tion. Other data sources used in this analysis are freely available for academic use: TRMM data are available from the NASA Mirador portal (http://mirador.gsfc. nasa.gov), ERA-Interim is available from the ECMWF data portal (http://apps. ecmwf.int/datasets/data/interim_-full_mnth/), DEM data used in this study are available from the WWF HydroSHEDS project (http://hydrosheds.cr.usgs.gov/ index.php), and the University of Delaware Climate Dataset is available for download at the Department of Geography Center for Climatic Research website (http://climate.geog.udel.edu/ ~climate/). GNIP isotopic data are available from the IAEA-Water Resources Program (http://www-naweb.iaea.org/ napc/ih/IHS_resources_gnip.html). We acknowledge several funding sources for this work: RPF received an NSF Graduate Research Fellowship (grant 2011094378), a University of Michigan Graduate Student Research Grant, a University of Michigan Rackham Graduate School International Research Award, and two University of Michigan Department of Earth and Environmental Sciences Scott Turner Awards. C.J.P. and T.A.E. received support from NSF EAR grants 0738822 and 0907817. C.J.P. also received support through the University of Michigan Associate Professor Fund. We thank J. Tito, G. Gonzalez, and S. Tawackoli for field logistics and support; M.L. Jeffery, N. Insel, and M. Tracy for assistance in the field; and N. Insel for access to REMOiso model data.
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