Oxygen Isotope Ratios in Trees Reflect Mean Annual Temperature and Humidity

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Abstract
Values of the oxygen isotope ratios (δ 18 O) in tree-ring cellulose closely reflect the δ 18 O values in atmospheric precipitation and hence mean annual temperature. The change in δ 18 O in cellulose is 0.41 per mil per degree Celsius for selected near-coastal stations. The values of δ 18 O in precipitation and cellulose also change with altitude, as demonstrated for Mount Rainier, Washington. A temperature lapse rate of 5.2° ± 0.5°C per 1000 meters calculated from cellulose δ 18 O values agrees with the accepted mean annual lapse rate of 5°C per 1000 meters for this region. Cellulose δ 18 O values and δ 18 O values of carbon dioxide equilibrated with leaf water differ by a fixed 16 per mil.