STALAGMITE RECORDS OF CLIMATIC AND ENVIRONMENTAL CHANGES ON WESTERN SHANDONG PENINSULA IN THE PAST 1000 YEARS: LAMINA THICKNESS

The stalagmite of ky1,collected from the Kaiyuan Cave in the littoral of western Shandong Peninsula, North China,is located in the warm temperate zone of the East Asia monsoon.The upper part(0-42.769mm)of the stalagmite consists of 678 continuous layers of deposits,of which all are typical transparent annual layers.High precision dating was made with U-²³⁰Th technique together with continuous lamina counting.It is confirmed that the ages of the 1st and 678st lamina are 1217 AD and 1894AD respectively, which means that the upper part of the stalagmite ky1 was deposited in the time span from 1217AD to 1894AD,including the late Medieval Warm Period(MWP)and the whole Little Ice Age(LIA)exactly. According to the lamina thickness andδ¹⁸O variation,in the 678 layers from 1217AD to 1894AD,both the variation in lamina thickness of the stalagmite and the fluctuation of lamina thickness show an obvious periodical manner,and are synchronous with the summer monsoon intensity and precipitation.Negative correlation has been observed between the lamina thickness and summer monsoon intensity/precipitation.Thicker laminae are corresponding to weaker summer monsoon/less precipitation,and thinner ones corresponding to stronger summer monsoon/more precipitation.On the other hand,between the lamina thickness and the fluctuation of summer monsoon intensity/precipitation there is positive correlation.The period of thicker lamina formation is corresponding to higher fluctuation of summer monsoon intensity/precipitation, and vice versa.Therefore,for a cave like the Kaiyuan in the warm temperate zone of the East Asia monsoon, the variation in lamina thickness is related to the variation in climatic factors and climatic stability. In the warm temperate zone of the East Asia monsoon,the climate in LIA was less stable compared to MWP,in addition to less precipitation and low temperature.