Climate Change In The Past 1000 Years Revealed By Stalagmite From Kaiyuan Cave In Shandong Peninsula, China

Deposition of karst speleothem is the important files which recorded terrestrial climate and environment change during the geological history, especially the stalagmite records attracting the climate researchers’ attention,but the environmental implications there may be uncertainty or ambiguity. Stalagmite KY1 was collected from Kaiyuan Cave in western Shandong Peninsula, depending on analysis of the stalagmite oxygen and carbon stable isotope, trace elements and lamina thickness, we determined that the stalagmite grew up from 892-1894 AD about one thousand years. The main research results are as follow:(1) Throug the high precision dating with U-230 Th technique, we determined the stalagmite grew up from 892-1894 AD about one thousand years through the methods of lamina counting and interpolation/extrapolation of the average deposition rate, which corresponding Medieval Warm Period(MWP) and Little Ice Age(LIA). The δ18O and δ13C values of stalagmite KY1 showed obvious stage characteristics in recent 1000 years, exhibited a series of centennial to multicentennial climate fluctuations. According to the variation of δ18O and δ13C values of stalagmite KY1, the climate mutation occurred in about 1482 AD and 1494 AD respectively. δ18O showed the change of the summer monsoon intensity and the precipitation, the δ13C values showed the vegetation C3/C4 proportion and the change of its productivity in the study area. During the stalagmite sedimentary period, the record of climate fluctuation and replacement of the Chinese dynasties showed correspondence. In addition, the change of vegetation and soil system is not only affected by climate change, also can not ignore the impact of human activeties on it.(2) In this article, we discussed the climate significance of the stalagmite Mg/Sr, Sr/Ca, and analyzed climate change of the west of Shandong Peninsula from the end of the 9th century to the end of the 19 th century(892-1894AD) about one thousand years. Results show that the Mg/Sr of the stalagmite KY1 reflected the temperature change during the whole deposition process, which also was the good record of the temperature change between LIA and the MWP and their transformation in 1482 AD, the stalagmite Sr/Ca change reflected the variation of precipitation, and compared with cumulative departure curve of drought-waterlog index in historical period respectively. Stalagmite Sr/Ca showed significant correspondence with cumulative departure curve of drought-waterlog index in recent 500 years during the Little Ice Age, made the different climate regimes with the temperature change in different stages. During the whole deposition stage, the climate switch condition occurred between the period(892-936AD) which dominated the cold and dry climate and the period(936-1092AD) which was warm and dry from 892-1092 AD, then, the warm and wet climate often alternated with cold and dry climate during 1092-1894 AD on different time scales.(3) The change of the lamina thickness and its fluctuation degree showed low-high-low stage characteristics. And compared the result of the lamina thickness measurement with the δ18O value test,showed that the variation and its variation fluctuation degree of lamina thickness obvious synchronized with the summer monsoon intensity/precipitation and their fluctuation degree in same time. Therefore, the variation of lamina thickness of stalagmite KY1 were related to the variation of climatic factors themselves, and related to climate stability degree. In addition, the climate in LIA showed less precipitation and low temperature compared with MWP, it also showed obvious decreased trend for the climate stability degree.