| Abstract
| - Wine hydrogen and oxygen stable isotopes record the climatic conditions experienced by the grapevine 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 forindependently verifying claims of origin. We present the results of a study designed to evaluate therelationships between wine water δ18O and spatial climate and precipitation δ18O patterns acrossthe winegrape-growing regions of Washington, Oregon, and California. Retail wines produced fromtypically small vineyards across these regions were obtained from the 2002 vintage, and the δ18O ofwine water was analyzed using a CO2 equilibration method. Significant correlations were observedbetween the measured wine water δ18O from 2002 and the long-term average precipitation δ18O andlate 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 spatiallyin a GIS. The GIS model is the first of its kind and allows spatially explicit predictions of wine δ18Oacross the region. Because high spatial resolution monthly climate layers are now available for manyyears, wine δ18O could be modeled for previous years. We therefore tested the model by executingit for specific years and comparing the model predictions with previously published results for wineδ18O from seven vintages from Napa and Livermore Valleys, California. With the exception of oneyear, an anomaly potentially related to the effects of El Niño on precipitation isotopic composition,the model predicted well the wine δ18O for both locations for all vintages and generally reflected theconsistent enrichment of wine from Napa relative to Livermore. Our results suggest that wine waterδ18O records both source water δ18O and climate during the late stages of winegrape ripening andthat GIS models of wine water δ18O are useful tools for independently verifying claims of regionalorigin and vintage. Keywords: Stable isotope ratio; oxygen; water; spatial modeling; database; fraud; label
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