Seasonal variation in the total alkalinity and δ13CDIC values of cave drip water in a ventilated cave in response to the regional climatology, southwest China

Abstract

The simulation and monitoring of environmental proxies in cave systems is of great significance for understanding the controlling factors of stalagmite geochemistry and for further analysing the signal transmission process and mechanism in cave systems. In this study, we collected samples from three drip points in Liangfeng Cave from 2015 to 2020, Guilin City, Southwest China. The δ13CDIC values, total alkalinity and modern calcite deposition rates at the drip points in the cave were measured during the monitoring period. Comparison of these data with atmospheric temperature and rainfall data from the study area revealed that (1) the δ13CDIC and total alkalinity values of cave drip water show a seasonal pattern involving low values that increase in summer and autumn and high values that decrease in winter and spring, which is synchronized with the changes in the regional rainfall and temperature. (2) The modern calcite deposition rate also shows characteristics of significant seasonal variation. In addition, modern calcite deposition rate of drip water (site LF-4) decreased year by year. On an interannual time scale, the recharge regime of this drip water is likely to be the main control on the modern calcite deposition rate. (3) The δ13CDIC values of the drip water in Liangfeng Cave (well ventilated) are generally higher than those of another cave (weakly ventilated) in the study area for winter and spring. The cave ventilation effect leads to a higher δ13CDIC value in the drip water during times of low cave pCO2. (4) Because Liangfeng Cave is a well-ventilated cave, the drip water could record the seasonal regional climatology variation. Observations from the well-ventilated Liangfeng Cave provide a reference point for the interpretation of regional climatology signals from speleothem proxy records.