The Geochemical Process Of Stable Carbonic Isotopic Evolution In Karst Cave System And Its Environmental Meanings

As substitute index of environment, stable carbon isotope has been used broadly in different records, such as tree rings, peat and carbonate rock. Nowadays scholars have gradually used stable carbon isotope of speleothem in karst caves to discuss the changing history of palaeoclimate and palaeoenvironment, such as vegetation subrogation and the change of atmospheric CO2 concentration. However, the application of index is limited owning to lack of the study about formation mechanism in karst cave system. Taking cave systems under different vegetation in guizhou karst area as study objects, this paper analyzes the spatio-temporal evolution of stable carbon isotope in karst cave system. Vegetation of Liangfeng cave, Qixing cave, Xiniu cave and Jiangjun cave are respectively origin forest, bosk, grassplot and rocky desertification. Several results have been achieved as folio wings:1.The response of stable carbon isotope in karst cave system to surface climate and environment.This index can distinguish origin forest from other vegetation, but cannot distinguish transitional eco-environment such as bosk, grassplot and rocky desertification. It is showed that the 13C values of stalagmite can be used to discuss the changes of vegetation to some extent and more work should be done to the study of reconstruct-mechanism.The 13C values of speleothem under different drip in same cave are different. It showed that the detail situation of drip water should be taken into account using the 13C values of stalagmite to reconstruct palaeoclimate and palaeoenvironment. In this condition, the geochemical process of stable carbon should be studied in detail especially combined the chemical data of water. Thus the vegetation above cave can be reconstructed correctly by stable carbon isotope.The DIC 13C values of cave drip and pond become light with precipitation increasing. The 13C values of spring water, soil water, soil CO2 and soil respired CO2 become mostly heavy with precipitation increasing.The 13C values of cave pond and soil respired CO2 become light with air temperature increasing, because organism activity is more intensive when temperature increase.2. The temporal evolution of stable carbon isotope in karst cave system The 13C values of plants in October are heavier than those in July.The 8 C values of soil CO2 in Xiniu cave system and Jiangjun cave system show a peak in August. In our previous study in grassland soil profiles of Qingzhen Hongfeng Lake karst ecotope experimental station, the values are also heavier in August. In June, it is obvious lighter than other month's results in Liangfeng cave and Qixing cave, the reason is that the respiration of microorganism and plant's root is most stronger. The values of soil respired CO2 in June are lower than other month's results due to strong respiration of microorganism and plant's root.The 13C values of cave CO2 become low in August or September. The monthly change in Qixing cave is not obvious as other caves due to better connectivity with outside and the amplitude change is the largest in Liangfeng cave because of bad connectivity with outside.The DIC 13C values of soil water in September are lighter than other month's results and there is a peak in August in Liangfeng cave and jiangjun cave systems.The DIC 13C values of spring in Qixing cave have become gradually heavy from June, reach a peak in August and this peak also appears in Liangfeng cave in August. Compared with soil water, the light value of spring water does not appear in September but in October. The reason maybe is that spring water has already reached deep-level, its response to soil respiration is slower than soil water.The DIC 13C values of cave drip in different cave show different changing patterns, might be relative to different sources and different routes of drip water.The DIC 13C values of cave pond water reach minimum in July. Later the values gradually become heavy.3.The spatial evolution of stable carbon isotope in karst cave system.Different part of plants...