Moisture variations over the past millennium characterized by Qaidam Basin tree-ring delta O-18

High-resolution tree-ring delta O-18 chronologies covering the last millennium, although scarce, are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau. For this study, a tree-ring delta O-18 chronology with a temporal resolution of 3-years was developed from the long-lived Qilian juniper (Sabina przewalskii Kom.), extending back in time to AD 991. This long delta O-18 chronology was significantly correlated with the yearly delta O-18 in tree rings during the common period from 1800 to 2006, and was an effective proxy for relative humidity during the growing season. A low-frequency moisture pattern signified the occurrence of a slight drought during the Medieval Climate Anomaly, a marked occurrence of a wet period during the Little Ice Age, and a trend in increasing moisture levels, although lower than average, alongside the Twentieth Century warming trend. Comparisons to other hydroclimatic reconstructions indicate that this tree-ring delta O-18 chronology serves as a reliable paleo-humidity proxy for the Qaidam Basin as well as documenting details of past humidity levels in the region