Summer temperature variations recorded in tree-ring δ13C values on the northeastern Tibetan Plateau

The source region of the Yangtze River is experiencing ever-faster glacier retreat and land deterioration as a result of climate change; however, understanding the past climate variability in the region is still limited by lack of long-term climate records. Here, we report a temperature-sensitive annual stable carbon isotope (δ13C) series of Tibetan juniper (Sabina tibetica) tree rings from 1850 to 2002 in natural forests in the source region of the Yangtze River on the northeastern Tibetan Plateau. The stable carbon discrimination (Δ13C) is significantly negatively correlated with the regional mean summer (May, June, and July) temperature, as well as with large-scale temperature variations. The reconstructed mean summer temperature explained about 44.3% of the total variance. It also agreed well with neighboring temperature proxies, including the ice-core δ18O series from the Guoqu glacier and from Dasuopu glacier and other tree-ring proxies. The cold and warm periods indicated by the climate reconstruction also coincide well with documented glacier advances and retreats in the eastern and southeastern Tibetan Plateau. The significant correlations among the reconstructed temperature, sea surface temperature (SSTNino3), and the Southern Oscillation index suggest the influences of synoptic atmospheric circulation on low-frequency variations in temperature on the region of the Yangtze River.