Modeling δ18O in precipitation over the tropical Americas: 2. Simulation of the stable isotope signal in Andean ice cores

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Abstract
We use the ECHAM‐4 and the GISS II atmospheric general circulation models (AGCM) with incorporated stable isotopic tracers and forced with observed global sea surface temperatures (SST) between 1979 and 1998, to simulate the δ18O signal in three tropical Andean ice cores, from Huascarán (Peru), Quelccaya (Peru), and Sajama (Bolivia). In both models, the simulated stable isotopic records compare favorably with the observational data, when the seasonality of precipitation and dry season loss due to sublimation and wind scour are taken into account. Our simulations indicate a significant influence of the local climatic conditions (temperature and precipitation amount) on the δ18O signal. Moisture source variability appears to be less of a factor on interannual timescales. Even though the moisture originates over the Amazon basin and the tropical Atlantic, correlation fields with National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) Reanalysis atmospheric variables and SST data indicate a dominant tropical Pacific control on interannual timescales. More enriched (depleted) δ18O values are associated with periods of warm (cold) conditions in the tropical Pacific. This is consistent with modern observational evidence, which shows that climate and atmospheric circulation in the tropical Andes are closely correlated with SST anomalies in the tropical Pacific domain on interannual to interdecadal timescales. The growing number of stable isotope records from tropical Andean ice cores may thus provide an important archive for reconstructing Pacific climate variability.

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