The negative correlation between the local precipitation and speleothem δ18O 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 δ18O. In this study, regression analysis and corresponding significance test method are employed to investigate the relationship between the Asian summer monsoon circulation and speleothem δ18O of Xiaobailong cave using CERA-20C, speleothem δ18O of Xiaobailong cave, and precipitation and temperature data from 8 meteorological stations around the cave. Diagnostic results indicate that the speleothem δ18O 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 δ18O 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 δ18O in speleothems, ice cores, and tree ring cellulose.
Bibliographical noteFunding Information:
We thank Prof. K. Yoshimura for providing the isoGSM and three anonymous reviewers for their valuable comments that lead to improvement of the manuscript. This work was supported by the National Natural Science Foundation of China (41861144012, 41875103, U1502233 and 41888101), the Natural Science Foundation of Yunnan Province (2018FY001-018, 2018FB081, and 2018BC007), the program for Innovative Research Team in Science and Technology in University of Yunnan Province, and the Science Foundation of Education Department of Yunnan Province (2018Y002). Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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