The dendroclimatic value of oak stable isotopes

Abstract

Tree-ring stable oxygen and carbon isotope ratios (δ18O and δ13C) are an important archive for climate reconstructions. However, it remains unclear whether the polyvinyl acetate emulsion, often used for the preservation and fixation of wood samples, influences δ18O and δ13C signals. Further uncertainties are associated with the possible effects of geographical origin and cambial age of historical samples. Here, we present annually-resolved and absolutely-dated δ18O and δ13C measurements of 21 living oaks (Quercus robur and Q. petraea) from the Czech Republic. We find that the δ18O and δ13C signals in the extracted alpha-cellulose are not affected by polyvinyl acetate treatment. Covering the entire 20th century and reaching until 2018 CE, our dataset reveals spatial and temporal coherency within and between the individual δ18O and δ13C chronologies of different oak species, sample locations, and tree ages. Highly significant (p < 0.01) Pearson’s correlation coefficients of the site-specific δ13C and δ18O chronologies range from 0.48–0.77 and 0.36–0.56, respectively. The isotopic inter-series correlations of Q. robur and Q. petraea from the same site are 0.75 and 0.43 for the mean δ13C and δ18O values, respectively. Significant (p < 0.01) correlations of 0.49 and 0.84 are found for δ13C and δ18O, respectively, when all measurements from all sampling locations and tree ages are included. Our study shows that non-pooled oak δ18O and δ13C measurements from both species, different locations, and diverse tree ages can be combined into robust isotopic chronologies for climate reconstructions.