The dendroclimatic value of oak stable isotopes

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 20^th 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.