Twentieth-century summer temperature variability in the southern Altai Mountains: A carbon and oxygen isotope study of tree-rings

The Altai mountains, southern Siberia, represent an area of significant scientific interest and exceptional palaeoecological potential. To assess the influence of climate on the stable isotopic composition of tree-ring cellulose and the potential of this record as a palaeoclimate proxy, replicated stable oxygen and carbon isotope time-series were developed for the twentieth century from four Siberian Pine (Pinus sibirica Du Tour) trees growing near the settlement of Aktash, Russian Altai mountains, southern Siberia. Bootstrapped calibrations for the local instrumental period (AD 1954-2000) reveal strong correlations between summer (July-August) growing season temperatures and tree-ring oxygen (r(2) = 0.55) and carbon (r(2) = 0.30) isotopes. Covariance observed between both carbon and oxygen isotope data suggest a common (stomatal) control. The resulting empirical model was used to reconstruct regional summer temperatures for the twentieth century. No divergence is observed between the non-detrended tree-ring isotope series and instrumental data nor is there any twentieth-century summer warming trend. The strong isotopic signal preserved in the tree-ring series supports the wider application of this approach to explore climatic variability and environmental trends during past millennia through analysis of new and existing long tree-ring chronologies from this region.