INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Isotopic characterization of mountain precipitation along the eastern flank of the Andes between 32.5 - 35°S
HOKE G. D.; ARANIBAR J. N.; VIALE M.; ARANEO D.; LLANO C. L.
San Francisco, California
Encuentro; AGU Fall Meeting.; 2011
American Geophysical Union
Data describing the isotopic composition of precipitation in the Andes are sparse: on the South American continent one IAEA Global Network of Isotopes in Precipitation (GNIP) station above 1500 m elevation exists south of La Paz. Better spatial density is necessary to improve our understanding of isotopes in mountain precipitation, which has implications for how to interpret isotopic information from the geologic record and the validation of isotope tracking modules in climate models. We present finding from two-years of quasi-monthly precipitation collection on the eastern flank of the Andes between 32.5 and 35°S latitude. A total of 123 samples were collected from 10 stations from Setember 2008 until September 2010.North of 33°S, the 2500 m average elevation Precordillera forms a steep front orographic barrier and the 2000 m elevation Uspallata Valley separates the Precordillera from the high Andes to the East. South of 33°S the Precordillera ends and the Andes return to a simple linear morphology. The low-leeward (eastern) side of the Andes receives predominately summer precipitation from convective storms, usually triggered by daytime upslope flow or synoptic-scale easterly flow over the Precordillera. Moving westward from the lowleeward side to the range crest, the influence of the easterly summer precipitation wanes and winter spillover precipitation from mid-latitude westerly storms beings to dominate.Our results show the local meteoric water line is slightly steeper (~0.5) than the global meteoric water line and a y-intercept of 14. The most negative δ18O values vary as much as 15 per mil seasonally, while averages weighted by precipitation amount show a strong cross-barrier (elevation) dependence. At these latitudes, the weighted average precipitation δ18O values show a significant deviation from river water near the range crest. The influence of the different moisture sources, from synoptic-scale easterly or westerly flow, is distinguished by deuterium excess values, which are low at the crest and high at low-leeward side.Our data show that the overall trend of more negative values with increasing elevation is robust despite complicated moisture source trajectories at these latitudes in the Andes. Quaternary pedogenic carbonates show are in good agreement with precipitation data for elevations below 3000 m.