Relationship between the Asian summer monsoon circulation and speleothem δ18O of Xiaobailong cave

The negative correlation between the local precipitation and speleothem \( \delta^{18} {\text{O}} \) is used extensively in the study of monsoon variability. However, the correlation coefficient between them do not always pass the significance test, which makes it difficult to interpret the monsoon variability using speleothem \( \delta^{18} {\text{O}} \). In this study, regression analysis and corresponding significance test method are employed to investigate the relationship between the Asian summer monsoon circulation and speleothem \( \delta^{18} {\text{O}} \) of Xiaobailong cave using CERA-20C, speleothem \( \delta^{18} {\text{O}} \) of Xiaobailong cave, and precipitation and temperature data from 8 meteorological stations around the cave. Diagnostic results indicate that the speleothem \( \delta^{18} {\text{O}} \) of Xiaobailong cave can reflect the variability of Asian summer monsoon circulation via the rainout effect from the nearest upstream sources to destination. The stronger (weaker) ASM circulation causes isotopically depleted (enriched) water vapor via enhancing (reducing) the Rayleigh distillation processes during the transport of water vapor from the northern Bay of Bengal and the northern South China Sea to the region around the cave. The lower (higher) isotope value in water vapor further leads to depleted (enriched) speleothem \( \delta^{18} {\text{O}} \) of Xiaobailong cave. The numerical experiments using isotope-incorporated spectral model substantiate the key physical process revealed in the observational analysis. These results provide an efficient way for reconstructing the paleomonsoon circulation with \( \delta^{18} {\text{O}} \) in speleothems, ice cores, and tree ring cellulose.