Stable oxygen isotope interpretation of drip water sources and transport processes in Shawan Cave, Puding, Guizhou

Cave drip water is the primary source of material for stalagmite deposition, and its oxygen isotope composition(δ18O)is a key proxy for paleoclimate reconstruction using stalagmites. Analyzing the variation characteristics of δ18O in cave drip water and its relationship with atmospheric precipitation and transport processes provides essential support for interpreting the paleoclimate information recorded in stalagmite δ18O. This study analyzes the stable hydrogen and oxygen isotope compositions of atmospheric precipitation, cave drip water(collected from 5 drip water sites), and calcite precipitates(collected from 3 monitoring sites)from 2017 to 2020 in Shawan Cave(26.36°N, 105.76°E; entrance elevation ca.1170 m; bedrock thickness 6~8 m), Puding, Guizhou. Combined with the HYSPLIT backward trajectory model(based on 960 effective trajectories), it reveals the transmission and modification processes of δ18O signals from atmospheric precipitation to cave drip water in the regional water cycle. The main results are as follows: 1)Atmospheric precipitation δ18O exhibits more negative values in summer and more positive values in winter, primarily influenced by moisture sources, differences in transport pathways, and ENSO events. 2)Cave drip water δ18O shows an opposite seasonal pattern with significantly attenuated signal amplitude. The fitted hydrological residence time is approximately 135 days, indicating mixing of old and new water in the vadose zone, which leads to damping and delay of the isotopic signal. 3)On an interannual scale, the annual mean δ18O of drip water increased year by year from 2017 to 2020, which may be attributed to the gradual recovery of overlying vegetation at the site, leading to enhanced evapotranspiration. Therefore, when using stalagmite δ18O for paleoclimate reconstruction, it is necessary to comprehensively consider the combined influences of multiple factors, including seasonal changes in moisture sources, ENSO events, hydrological retention effects, and vegetation ecological processes.