Environmental Significance of δ¹⁸O Record from Cave Drip Water and Recent Carbonate Deposit at No.15 Branching Cave of Seven Star Cave in Guilin

Key words: 
• the meteoric precipitation /
• drip water /
• recent carbonate deposit /
• oxygen isotopes /
• No.15 branching cave

Abstract: A prerequisite for the dynamic monitor of modern cave is to provide a reliable basis for the interpretation of a variety or multiple proxies from modern carbonate (CaCO₃) sediment-stalagmites in cave, and to make full use of the multiple proxies from modern carbonate (CaCO₃) sediment in field cave monitoring, and compared to local measuring meteorological data each other and correction, is the key of the accurate and quantitative interpreting multiple climate proxies in stalagmites.
The four hydrological years of the meteoric precipitation, cave drips, modern carbonate sediments for 5 sites in No.15 branching cave of Seven Star Cave in Guilin during 2008-2011 were continuously monitored, and the correlation between the δ¹⁸O of cave drip and modern carbonate (CaCO₃) and δ¹⁸O of the meteoric precipitation were also discussed. The study results have shown that the annual average δ¹⁸O value of cave drip and modern carbonate (CaCO₃) is very close to δ¹⁸O of the meteoric precipitation and the same change trend, and indicated that the δ¹⁸O of cave drip and modern carbonate (CaCO₃) came mainly from δ¹⁸O of the meteoric precipitation, that is, it is obviously controlled by δ¹⁸O of the meteoric precipitation.
In four hydrological years, the year (or annual) change and or many years change trends of δ¹⁸O record from the modern secondary chemical carbonate sediments (CaCO₃) and drop water in cave are basically the same and show obvious change characteristics of four peak (low value area of δ¹⁸O) and four trough (high value area of δ¹⁸O), and has obvious rule of the seasonal change and year change and has the same seasonal characteristics of the meteoric precipitation or heat. The research results shown that δ¹⁸O of drip water and modern carbonate (CaCO₃) sediments in cave can record the climate change signal at local or at the top of the cave. So that it has been considered that δ¹⁸O of modern carbonate (CaCO₃) sediment in cave is mainly taken as the alternative proxies of the summer monsoon intensity and rainfall amount.