Study On Climate And Environment Recorded In Surface Tufa At Luoping, Yunnan

Tufas are attracting attention as potential environmental indicators, since their morphological and geochemical characteristics (stable isotopes and ratios of trace elements) reflect the climatic conditions during the period of their growth such as ambient temperature, precipitation, discharge or possible anthropogenic influences. And the content of heavy metals within tufas can indicate the pollution degree of river from which tufas deposited.A continuous52-year record (1958～2009) of stable isotope compositions of carbon and oxygen (d13C、d18O), as well as ratios of trace elements (Mg/Ca、Mg/Sr) in a laminated tufa precipitated at Jiulong waterfall, Yunnan, is presented. Geochemical records have been compared to hydrometeorological data, available for the last52years. An attempt is made to relate variations of geochemical records in tufa to environmental parameters, such as temperature and precipitation. The analysis results which agreed with conclusions obtained by former experts showed that oxygen and carbon stable isotopes (d13C、d18O) had negative correlation with temperature and precipitation respectively, whereas trace elements ratios (Mg/Ca、Mg/Sr) were positively correlated with temperature, but Mg/Ca ratio was negatively correlated with precipitation. The above corresponding relationship between geochemical indicators and weather data was used to restore climate changes during the period of tufa growth (1908-2009) in Luoping aera, with the help of carbon and oxygen stable isotopes composition (d13C、d18O) and rations of trace elements (Mg/Ca、Mg/Sr) of the tufa deposited in Jiulong waterfall group.We inferred the centennial-scale climate change scenarios in Luoping region from two different time-scales, the holistic trend and further subdivided into9stages, respectively:(a) In the whole, both d18O and d13C made positive offsets indicating that temperature and precipitation declined the last100years in Luoping;(b) From the stage point of view, the regional climate change was subdivided into9phases and exhibited as follows:warm and wet�'cool and dry�'hot and humid�'cool and semiarid�'warm and rainy�'cool and damp�'cold and arid�'semi-cold and wet�'warm and dry. The climate in this region had approximately gone through4times climate cycles between warm and wet-cold and dry. Meanwhile, the temperature within last nearly100years in this area should be declined in a small amplitude, based on the fact that the ratios of Mg/Ca and Mg/Sr presented a downward trend in different degrees, which was consistent with the, while the amount of precipitation should increase disagreed with the inferred result speculated by using carbon isotope, and the reason was unknown. Besides, the contents of Pb%Cr in tufa had an upward trend, implying that contamination of the river where Jiulong waterfall belongs is getting heavier. This may be because of the cause that the development of beauty spot leads to the surge in the number of visitors who discard increasing garbage and wastes bringing environmental problems.This article believed that carbon and oxygen stable isotopes and trace elements ratios in the laminated tufa, as good study carriers of high-resolution climate change, could record local temperature and rainfall. However, the hiatus in tufa and meteorological data which was difficult to obtain were important factors constraining this study, which desiderated resolutions the next step.