Potential linkages between the moisture variability in the northeastern Qaidam Basin, China, since 1800 and the East Asian summer monsoon as reflected by tree ring δ18O

We established the first annual resolution tree ring delta O-18 chronology of Qilian juniper (Sabina przewalskii Kom.) for the eastern margin of the Qaidam Basin, northwestern China. The mean tree ring cellulose delta O-18 in the study region (33.46 parts per thousand +/- 0.99 parts per thousand) was higher than that in the Qilian (28.7 parts per thousand) and Helan Mountains (27.66 parts per thousand), northwest China, and higher than the values in other published research (15.0 parts per thousand to 33.0 parts per thousand), possibly as a result of the heavier delta O-18 in precipitation and the lower relative humidity (43%) during the growing season. The results of our simple correlation, bootstrap correlation, and response analyses showed that the cellulose delta O-18 was negatively and significantly correlated with relative humidity in July and August and that this correlation explained about 31.4% of the total variance in the moisture variability from 1954 to 2006. We also detected significant correlations among the Palmer drought severity index, the standard precipitation index, and the tree ring delta O-18 series. These analyses revealed that the summer relative humidity was the main limiting factor that affected delta O-18 values in the tree ring cellulose. Previous research indicates that the direct influence of the East Asian summer monsoon (EASM) reaches as far west as 100 degrees E in China. However, our study revealed that the tree ring delta O-18 series was significantly correlated with the EASM index from 1873 to 1975, which means that the EASM influences moisture variability in the Qaidam Basin (farther west than 100 degrees E) and that the tree ring delta O-18 chronology we obtained can be used as a proxy to study historical variability in the EASM.