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 δ¹⁸O in the East Asian Summer Monsoon (EASM) region is a crucial issue restricting stalagmite-inferred paleoclimate research. The connection between El Niño Southern Oscillation (ENSO) and monsoonal precipitation/cave δ¹⁸O 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 δ¹⁸O 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 δ¹⁸O (δ¹⁸O_p). The δ¹⁸O_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 δ¹⁸O (δ¹⁸O_d) is irregular, and its amplitude is much smaller than that of δ¹⁸O_p. The δ¹⁸O_d can reflect integrated δ¹⁸O_p changes within the residence time of rainwater in the karst reservoir and can inherit the ENSO signal in δ¹⁸O_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 δ¹⁸O_d to ENSO activities, with a shorter time lag and greater amplitude. The modern calcite δ¹⁸O (δ¹⁸O_c) series show significant seasonal variations controlled by the fractionation coefficient varied with cave temperature. On the inter-annul time scale, the change of δ¹⁸O_c is mainly controlled by δ¹⁸O_d and can record the ENSO-related variations. Our findings imply that high-resolution stalagmite δ¹⁸O reconstructions from Yuhua Cave may be able to identify historical ENSO-related variability in the EASM on annual to decade time scales.