Potential ENSO effects on the oxygen isotope composition of modern speleothems: Observations from Jiguan Cave, central China

Despite of the fast development of speleothem records, oxygen isotope (δ18O), the main paleoclimatic proxy, remains complicated in climatic interpretation. Continuous cave monitoring is essential for understanding the response of stalagmite oxygen isotope to East Asian Summer Monsoon moisture transportation. We introduce a 7 years (2010-2016) study on oxygen isotope of atmospheric precipitation, cave drips and modern speleothems at Jiguan Cave, central China, located Chinese north-south divide where is sensitive to Asian Monsoon. The monitoring covered a whole ENSO (El Niño Southern Oscillation) cycle, from El Niño in 2010 to La Niña in 2011 and recovered another El Niño in 2015. The precipitation δ18O shows obvious seasonality (negative in summer and positive in winter), but air temperature and rainfall amount are not primary controlling factors. The interannual δ18O of precipitation corresponds with ENSO variability, which means δ18O value is positive during El Niño event and vice versa. We used HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model to simulate the moisture transportation for rainy season in El Niño and La Niña years, and found the Pacific contributed over 50% moisture in El Niño years and the Indian Ocean was the predominant oceanic source in La Niña year. There is no seasonality in drips δ18O value, while the response to ENSO variability is evident on interannual scale. The stable negative δ18O of drips compared with precipitation indicate there is a threshold for infiltration, suggesting cave drips are recharged by summer heavy precipitation with light δ18O value, but it's the mixture of latest and former rainy precipitation that recharge drips in drought, which has been verified by simple infiltration model. We found the modern speleothems were precipitated under nonequilibrium fractionation during drought years, nevertheless, they can record the El Niño related δ18O positive anomaly. Overall, the modern speleothems can receive the precipitation δ18O signal transferred by drips, and our study offers significance for verification of Asian Summer Monsoon driving force and interpretation of stalagmite δ18O.