Impacts of cave ventilation on drip water delta C-13(DIC) and its paleoclimate implication

The speleothem stable carbon isotope (delta C-13) is an important proxy for paleoclimate reconstruction. Understanding the stable carbon isotope composition of dissolved inorganic carbon (delta C-13(DIC)) in drip water is crucial for the interpretation of speleothem 813C signals. In this study, we present two years of drip water delta C-13(DIC) data and its hydrogeochemistry variables (e.g. PCO2, Ca2+, Mg/Ca, SO42-, pH, drip rate, saturation index of calcite, electrical conductivity) in the Shawan Cave. We also conducted continuous in situ monitoring of PCO2 in the atmosphere, soil air, and cave air and microenvironmental factors. The results show that cave air CO2 primarily originates from soil air CO2, but there is an unsynchronous seasonal variation between cave air CO2 and soil air CO2, which is likely caused by cave ventilation. Cave ventilation is also responsible for seasonal variations in drip water delta C-13(DIC) and speleothem growth. Cave air exchange leads to higher drip water delta C-13(DIC) and rapid speleothem growth in the spring and summer seasons, and cave air stagnation results in lower drip water delta C-13(DIC) and slow speleothem growth. The impact of isotopically light CO2 of soil air on drip water delta C-13(DIC) during spring and summer seasons is more than during autumn and winter seasons, where the more isotopically light CO2 of soil air is enriched by drip water under cave air exchange conditions. Since speleothems growth is rapid in the spring and summer seasons, the speleothems delta C-13 of the Shawan Cave have the potential to record climate information for the spring and summer seasons. Additionally, by comparing the speleothem delta C-13 values of eleven caves, we found that paleoclimate signals recorded by speleothem delta C-13 revealed different seasonal biases under different ventilation types. Therefore, it is necessary to determine the cave ventilation type in order to und erstand how speleothem delta C-13 responds to climate change in a ventilated cave.