Monitoring in natural and artificial caves reveals cave microenvironment signals reflected in drip water

It is essential to distinguish the effects of climate signals and cave microenvironments on speleothem δ¹⁸O, δ¹³C, and element/Ca records, because cave microenvironments can interfere with the reconstruction of climate signals preserved by speleothems. However, it remains difficult to separate the impacts of direct climate signals and cave microenvironments-including cave air temperature and CO₂ concentration-on these proxies, even after numerous cave monitoring and laboratory simulation experiments. In this study, we compared outdoor Artificial Cave monitoring with natural cave monitoring, providing an innovative and efficient method to discriminate the effects of climate signals and cave microenvironments on the proxies. We presented seven years of time-series data from Shawan Cave (natural cave) and more than two years of time-series data from the outdoor Artificial Cave located in Guizhou Province, Southwest China, for δ¹⁸O, δ¹³C, and elemental compositions of cave drip water along with microenvironmental conditions. In Shawan Cave, the seasonal changes in drip water δ¹⁸O and δ¹³C_DIC, which showed a significant inverse correlation with cave air p CO₂, were attributed to the wide range of cave air p CO₂ (972–21,627 ppm), The irregular seasonal changes in drip water Mg/Ca were affected by the opposing seasonal variations in rainfall amount and cave air p CO₂. In contrast, in the Artificial Cave, the wider range of cave air temperature (11.78–25.25 °C) appeared to influence the seasonality of cave water δ¹⁸O and Mg/Ca values. Meanwhile, the δ¹⁸O and Mg/Ca values of water isolated from the cave were mainly affected by rainfall δ¹⁸O and rainfall amount, respectively. The δ¹³C_DIC values in cave water and in water isolated from the cave were primarily influenced by rainfall amount, because the narrow range of cave air p CO₂ was insufficient to drive a notable change in cave water δ¹³C_DIC. Our study highlights that cave microenvironments, rather than direct climate signals, are key drivers of seasonal amplitudes in speleothems proxies in caves with wide ranges of cave air temperature and p CO₂. When the ranges of cave air temperature and p CO₂ are narrow, speleothem proxies primarily record precipitation and air temperature.