Oxygen isotope variability in precipitation, dripwater, and modern calcite responding to ENSO based on 11 years' monitoring in Yuhua Cave, Southeast China

The scientific explanation of cave & delta;O-18 in the East Asian Summer Monsoon (EASM) region is a crucial issue restricting stalagmite-inferred paleoclimate research. The connection between El Nino Southern Oscillation (ENSO) and monsoonal precipitation/cave & delta;O-18 and the mechanism involved also remain contentious. Long-term cave monitoring is an effective solution to deal with these issues. Here, we present 11-year-long precipitation, dripwater, and modern calcite & delta;O-18 data from Yuhua Cave in Southeast China, located in the frontal zone affected by the EASM. The upstream convection and rainout processes mainly regulate seasonal and interannual variations in precipitation & delta;O-18 (& delta;O-18(p)). The & delta;O-18(p) series shows a strong response to EASM activities associated with the Intertropical Convergence Zone migrations and the activities of the West Pacific Subtropical High affected by ENSO activities. Due to the influence of the epikarst reservoir mixing effect, the seasonal variation of dripwater & delta;O-18 (& delta;O-18(d)) is irregular, and its amplitude is much smaller than that of & delta;O-18(p). The & delta;O-18(d) can reflect integrated & delta;O-18(p) changes within the residence time of rainwater in the karst reservoir and can inherit the ENSO signal in & delta;O-18(p). The inferred recharge models for the Yuhua drip sites reveal differences in the response to ENSO in terms of both timing and amplitude, which can be attributed to variations in the residence time of rainwater and the mixing ratio of new and old water within the karst aquifer. Higher rainfall would lead to a more sensitive response of & delta;O-18(d) to ENSO activities, with a shorter time lag and greater amplitude. The modern calcite & delta;O-18 (& delta;O-18(c)) series show significant seasonal variations controlled by the fractionation coefficient varied with cave temperature. On the inter-annul time scale, the change of & delta;O-18(c) is mainly controlled by & delta;O-18(d) and can record the ENSO-related variations. Our findings imply that high-resolution stalagmite & delta;O-18 reconstructions from Yuhua Cave may be able to identify historical ENSO-related variability in the EASM on annual to decade time scales.