最近千年来山东半岛西部气候环境变化的石笋微层厚度记录

ky1石笋采自位于暖温带东亚季风影响下的山东半岛西部开元洞,自顶部到距顶42.769 mm处发育有连续沉积的678个微层,均为典型的透光年纹层。在高精度U-230Th测年结果的基础上,结合年纹层的连续计数,确定第1、678纹层的沉积年代分别为1217AD、1894AD,即ky1石笋上部微层的沉积时间为1217-1894AD,恰好涵盖中世纪暖期后期和小冰期。根据微层厚度及δ18O比值测试结果,在1217-1894AD的678年中,ky1石笋微层的厚度变化和厚度的波动程度变化均具有显著的阶段性,而且与同期夏季风强度、降水量及其波动程度变化同步。其中,微层厚度与夏季风强度、降水量本身呈负相关,微层厚度高值期对应夏季风微弱-偏干期,而低值期对应夏季风强烈-偏湿期。另一方面,微层厚度与夏季风强度、降水量的波动程度呈正相关,微层厚度高值期对应夏季风强度、降水量的高波动期,而低值期对应夏季风强度、降水量的低波动期。因此,除与气候因子本身变化有关外,开元洞石笋微层厚度变化还与气候的稳定程度有关。在暖温带东亚季风区沿海,小冰期与中世纪暖期的气候差异,除了表现为降水减少、温度降低以外,还表现为气候稳定程度的显著降低。

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.