Aerial decay influence on the stable oxygen and carbon isotope ratios in tree ring cellulose

Sub-fossil wood is often affected by the decaying process that introduces uncertainties in the measurement of oxygen and carbon stable isotope composition in cellulose. Although the cellulose stable isotopes are widely used as climatic proxies, our understanding of processes controlling their behavior is very limited. We present here a comparative study of stable oxygen and carbon isotope ratios in tree ring cellulose in decayed and non-decayed wood samples of Swiss stone pine (Pinus cembra) trees. The intra-ring stable isotope variability (around the circumference of a single ring) was between 0.1 and 0.5‰ for δ18O values and between 0.5 and 1.6‰ for δ13C values for both decayed and non-decayed wood. Observed intra-tree δ18O variability is less than that reported in the literature (0.5-1.5‰), however, for δ13C it is larger than the reported values (0.7-1.2‰). The inter-tree variability for non-decayed wood ranges between 1.1 and 2.3‰ for δ18O values, and between 2 and 4.7‰ for δ13C values. The inter-tree differences for δ18O values are similar to those reported in the literature (1-2‰ for oxygen and 1-3‰ for carbon) but are larger for δ13C values. We have found that the differences for δ18O and δ13C values between decayed and non-decayed wood are smaller than the variation among different trees from the same site, suggesting that the decayed wood can be used for isotopic paleoclimate research.