Transmission Of Oxygen Isotope Signal In Precipitation-drip Water-speleothem In Yuhua Cave

With high precision and absolute dating scale, stalagmite profiles have became the benchmark of paleoclimate intercomparison in paleoclimate study, and have also became a prop out of the three big props of paleoclimate study such as ice cores, loess and marine sediments. Particularly, a series of original works about Chinese stalagmite Monsoon records, published in Science or Nature, has attracted a great deal of attention in Quaternary science. However, there is still considerable debate about the interpretation of the δ18O in these works, and then become a huge challenge to the drive mechanism built on the stalagmite oxygen records by Chinese scientists. Cave monitoring is one of the main ways to solve the scientific problem.Located in the southeast coast and on the forefront of landing site of East Asian summer monsoon, Yuhua Cave is quite sensitive to the advance and retreat of East Asian summer monsoon. As a result, it has been considered to be an ideal place for studying the climatic significance of Speleothem.This thesis chooses Yuhua Cave as its study object, analyzes the characteristics of areal precipitation-drip water- Speleothem and the features and changes of δ18O, and discusses the signal transition and its influential factors of stable isotope of oxygen among precipitation-drip water-Speleothem, drawing conclusions as shown below:1. The LMWL of Yuhua Cave:δD=8.87δ18O+17.59(R2＝0.97)with a high slope and intercept; aqueous vapour distils mainly under thermodynamic equilibrium, and the precipitation is subject to smaller impact of revaporization.2. The values of δ18O of precipitation of Yuhua Cave unanimously skew positively in2011and from October to December in2012, which reflect the retreat of summer monsoon and the establishment of winter monsoon. The values of δ18O in precipitation of Yuhua Cave unanimously skew negtively in2011and from May to June in2012, and the values on June,2012and at the beginning of July2013are-8.42‰and-8.99‰respectively, which reflect the weakness of winter monsoon and the reinforcement of summer monsoon. In a word, the seasonal variation of δ18O of precipitation of Yuhua Cave reflects the growth and decline of winter monsoon and summer monsoon.The precipitation of Yuhua Cave tends to be heavier in spring while be lighter in summer. The weighted average value of δ18O of precipitation from December2011to mid-May2012is-5.66‰; from June to November in2011; the value derived from three periods (from July to November2011, from June to November2012, and from June to September2013) is-9.02‰. The great differences between them reflect that of δ18O composition of precipitation, which is under the control of winter or summer monsoon.The values of δ18O of precipitation during study period are negative, which presented on November,2011. Those negative values may be the result of both the growth of precipitation and the reinforcement of southwest warm and moist air current brought about by great circulation changes, which is caused by sea surface temperature anomaly.3. The values of δ18O of drip water and Speleothem tend to be heavier in winter and spring (the mean values of δw18O of drip water in MLSB and JGT are-6.43‰and-6.27‰respectively; The mean values of δ18O of Speleothem are-4.44‰and-4.79‰respectively) while be lighter in summer and autumn (the mean values of δw18O of drip water in MLSB and JGT are-6.94‰and-6.60‰respectively; The mean values of δ18O of Speleothem are-4.93‰and-5.57‰respectively).4. The seasonal variation of δ18O in Speleothem in Yuhua Cave can well reflect the characteristics of seasonal changes of δ18O of rainfall, which distinctively tend to be negative in the end of spring and the beginning of summer, and be positive after late autumn. The seasonal fluctuations of δ18O in Speleothem in Yuhua Cave reflect both advance and retreat and transition of winter monsoon and summer monsoon.