摘要 : Stable carbon isotopic composition (delta C-13) of speleothems has often been recognized as a proxy of vegetation and soil processes in many climatic regimes. In monsoonal regions, the speleothem delta C-13 records are thought to ... 展开 Stable carbon isotopic composition (delta C-13) of speleothems has often been recognized as a proxy of vegetation and soil processes in many climatic regimes. In monsoonal regions, the speleothem delta C-13 records are thought to be able to document changes in local and/or regional precipitation as well. Due to the complexity of carbon isotopic evolution within heterogeneous karst aquifers, accurate interpretations of this proxy are challenging. It is essential to carry out detailed monitoring of cave dripwater delta C-13(DIC) to disentangle various processes governing carbon isotopic evolution and decipher the hydroclimatic constraints. Here, we reported the results of a five-year monitoring of the delta C-13(DIC) as well as hydrochemical compositions of dripwaters in the Maomaotou Big Cave, Guilin, South China. Great spatiotemporal variations in the dripwater delta C-13(DIC) values were observed: (i) seepage flow-fed drips commonly had lower delta C-13(DIC) values, with smaller temporal variation; (ii) the lowest delta C-13(DIC) values were found at fracture-fed drips that had a large supply of soil CO2, whereas the fracture-fed drips with less, episodic CO2 recharge had much more positive delta C-13(DIC); (iii) the delta C-13(DIC) exhibits remarkable season changes, particularly at fracture-fed drips where higher delta C-13(DIC) values were observed in winter seasons; and (iv) an increasing trend in mean value of delta C-13(DIC) at individual sites during 2015-2019 was found. Both hydrochemical and isotopic analyses revealed that the dripwater delta C-13(DIC) is mainly controlled by spatiotemporal variations in water-CO2-rock interactions in association with hydrological processes, coupled with soil CO2 dynamics, which are closely linked to changes in local rainfall at monthly to annual timescales. Prior calcite precipitation (PCP) along the flow path above the cave could also affect the delta C-13(DIC) of fracture-fed dripwaters in dry periods. Comparisons of the dripwater delta C-13(DIC) records with local climate showed that the change of summer monsoonal rainfall, particularly the August-September-October precipitation, significantly influences the annual mean delta C-13(DIC) value of dripwaters in caves of South China. Further comparison analyses of dripwater delta C-13(DIC) records from both southern and northern China suggested that variations of dripwater delta C-13(DIC) could reflect changes of regional monsoonal precipitation over inter-annual (and maybe decadal) timescale. This demonstrates that the delta C-13 of speleothems, if precipitated at isotopic equilibrium and not greatly influenced by the CO2 degassing, is likely to be a valuable proxy of monsoon rainfall variability across East Asia. 收起