A 210-year tree-ring δ18O record in North China and its relationship with large-scale circulations

Tree-ring stable oxygen isotope (delta O-18(TR)) demonstrates the enormous potential for revealing hydrological climate changes and large-scale atmospheric circulations. Here, we established the 210-year delta O-18(TR) chronology of Pinus tabulaeformis Carr. in Baotou, southwest Inner Mongolia, North China. The regional precipitation delta O-18 (delta O-18(P)) and June-July-August relative humidity (RHJJA) were the two dominant environmental factors controlling the delta O-18(TR) changes. Since the 1930s, the increasing delta O-18(TR) values in the study region reflected the drying trend due to reducing precipitation and increasing temperature. The delta O-18(TR) series in Baotou generally exhibited stronger correlations with three Indian summer monsoon (ISM) indexes than three East Asian summer monsoon (EASM) indexes during 1948-2009 AD. However, the delta O-18(TR) record also significantly correlated with one EASM index. These results indicated that the Asian summer monsoon played an essential role in modifying the delta O-18(TR) values, and the ISM possibly had more considerable influence compared with the EASM. We also found that the delta O-18(TR) record had a higher correlation with the central-Pacific El Nino-Southern Oscillation (ENSO) than that with eastern-Pacific ENSO, probably because of the more substantial impact of the central-Pacific ENSO on the ISM.