VARIATION OF δ13C IN PLANT-SOIL-CAVE SYSTEMS IN KARST REGIONS WITH DIFFERENT DEGREES OF ROCKY DESERTIFICATION IN SOUTHWEST CHINA AND IMPLICATIONS FOR PALEOENVIRONMENT RECONSTRUCTION

Speleothem delta C-13 has been taken as an indicator of the history of rocky desertification, and changes in delta C-13 have been thought to reflect the transition between C3 and C4 surface vegetation types. In this study the delta C-13 values of plants, soil organic matter (SOM), dissolved inorganic carbon (DIC) of waters and modern calcite deposits in caves were investigated at five sites with different rocky desertification degree (RDD) in Southwest China. The main results can be summarized as follows: (1) dominant vegetation was the C3 type, with average plant delta C-13 values ranging from -26 parts per thousand to -32 parts per thousand (V-PDB), and SOM delta C-13 values ranging from -20 parts per thousand to -25 parts per thousand (V-PDB) for all the sites; (2) large variation for the delta C-13 of DIC from drip water and modern calcite deposits in caves, which must be the result of multiple, inorganic factors in the epikarst zone and not the local vegetation type; (3) a proposed conceptual model to demonstrate that the evolution of Asian summer monsoon (ASM) can be recorded in speleothem delta C-13 due to changes in epikarst zone hydrological conditions, exerting influence on stable carbon isotopes' fractionation, and not necessarily due to changing vegetation types in the subtropical zone of Southwest China.