Geography and vintage predicted by a novel GIS model of wine delta18O.
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Wine hydrogen and oxygen stable isotopes record the climatic conditions experienced by the grape vine and the isotopic composition of the vine's source water during berry development. As such, stable isotopes have been explored extensively for use in detecting wine adulteration or for independently verifying claims of origin. We present the results of a study designed to evaluate the relationships between wine water delta18O and spatial climate and precipitation delta18O patterns across the winegrape-growing regions of Washington, Oregon, and California. Retail wines produced from typically small vineyards across these regions were obtained from the 2002 vintage, and the delta18O of wine water was analyzed using a CO2 equilibration method. Significant correlations were observed between the measured wine water delta18O from 2002 and the long-term average precipitation delta18O and late season 2002 climate, based on a spatial join with continuous geographic information system (GIS) maps of these drivers. We then developed a regression model that was implemented spatially in a GIS. The GIS model is the first of its kind and allows spatially explicit predictions of wine delta18O across the region. Because high spatial resolution monthly climate layers are now available for many years, wine delta18O could be modeled for previous years. We therefore tested the model by executing it for specific years and comparing the model predictions with previously published results for wine delta18O from seven vintages from Napa and Livermore Valleys, California. With the exception of one year, an anomaly potentially related to the effects of El Nio on precipitation isotopic composition, the model predicted well the wine delta18O for both locations for all vintages and generally reflected the consistent enrichment of wine from Napa relative to Livermore. Our results suggest that wine water delta18O records both source water delta18O and climate during the late stages of winegrape ripening and that GIS models of wine water delta18O are useful tools for independently verifying claims of regional origin and vintage.
