Cave Monitoring in the Monsoon Region of China and Its Paleoclimatic Implications

Cave monitoring is essential for accurately interpreting the significance of proxies in stalagmite records. Here, we have compiled published monitoring data from 14 caves in the monsoon region of China (MRC), including cave air temperature (Tin ), cave air relative humidity (RH), cave air CO2 concentration (PCO2 ), multiple proxies (δ18O, δ13C, Trace element (TE)/Ca) in drip water and associated modern calcite, to serve as a reference for the stalagmite paleoclimate studies. The seasonal variations in these monitoring parameters were demonstrated through a carefully selected 24-month observation period at the cave sites. The seasonal variations in Tin , RH, and cave air PCO2 mainly depended on the local climate conditions and the degree of cave ventilation or tourist activities. Furthermore, the type and degree of ventilation were regulated by the site-specific karst structure system, such as the size of fractures, fissures, entrances and their relative altitude. The spatial-temporal variations observed in the behavior of δ18O, δ13C and TE/Ca in drip water and modern calcite can be attributed to the unique processes and environment prevailing within each cave. These in-cave processes and environment, including prior calcite precipitation (PCP), incongruent calcite dissolution (ICD), water-rock interaction (WRI), evaporation, drip rates, and calcite growth rates, are intricately related to the surface climate or hydrological conditions. Before applying geochemical proxies in stalagmites to paleoclimatic reconstruction, it is essential to ascertain the response mechanism of these geochemical proxies to those in-cave processes and surface climate or hydrological conditions, in addition to the replication test. More comprehensive cave monitoring studies with systematic design and longer durations are necessary for improving interpretations of proxies preserved in stalagmites.