Influence of weather on the stable isotopic ratios of wines: Tools for weather/climate reconstruction?

Precipitation, local ground water, soil water, atmospheric water vapor, gra pe leaf and grape berry water just prior to harvest, and grape must during the wine-making process, from the Napa Valley in northern California were c ollected for stable isotopic analysis. In addition, 27 red wines and 4 whit e wines produced in the Napa Valley, and 8 red wines produced in Livermore Valley located over 110 km to the southeast, were analyzed for both oxygen and hydrogen isotopic compositions. The isotopic compositions of the grape leaf water fall on a transpiration line with a slope of 2.1, while those of the grape berry water fall on a transpiration line with a slope of 2.8. Th e stable isotopic compositions of the 27 red wines from the Napa Valley ran ge from -3 to +20 parts per thousand in delta D and from +4.6 to +10.2 part s per thousand in delta(18)O and plot along a line described by delta D = 3 .4 delta(18)O -17.2. The maximum difference in the stable oxygen compositio n between two wineries 110 km apart is only 1.4 parts per thousand, while t he differences between the vintage years within each winery are 4.8 and 5.8 parts per thousand in delta(18)O. The stable isotopic composition of the g rape water is controlled by transpiration in the weeks prior to harvest, ov ershadowing all other effects. As a result of the timing of harvest, the re d wines are some 4 to 5 parts per thousand more enriched in delta(18)O than the white wines.