The climate reconstruction in Shandong Peninsula, northern China, during the last millennium based on stalagmite laminae together with a comparison to δ18O

Abstract

Stalagmite ky1, with a length of 75ĝ€mm and the upper part (from top to 42.769ĝ€mm depth) consisting of 678 laminae, was collected from Kaiyuan Cave in the coastal area of Shandong Peninsula, northern China, located in a warm temperate zone in the East Asia monsoon area. Based on high-precision dating with the U-230Th technique and continuous counting of laminae, the 1st and 678th laminae have been confirmed to be ADĝ€894ĝ€-±ĝ€20 and 1217ĝ€±ĝ€20 from top to bottom, respectively. By the measurement of laminae thickness and δ 18O ratios, we haved obtained the time series data of thickness of laminae and δ18O ratios from ADĝ€1217ĝ€±ĝ€20 to 1894ĝ€±ĝ€20, analyzed the climatic-environmental meaning of variations in the thickness of laminae, which have a good correspondence with the cumulative departure curve of the drought-waterlog index in the historical period. The results show that, in the ĝ1/4 ĝ€678 years from ADĝ€1217ĝ€±ĝ€20 to 1894ĝ€±ĝ€20, both the thickness of the laminae and the degree of fluctuation in the thickness of the laminae of stalagmite ky1 have obvious stages of variation and are completely synchronized with the contemporaneous intensity of the summer monsoons and precipitation as time changed. There is a negative correlation between the thickness of the laminae and the summer monsoon intensity and precipitation. There is a positive correlation between the degree of fluctuation in the thickness of the laminae and both the intensity of the summer monsoons and the precipitation. Therefore, for the Kaiyuan Cave in the coastal area of both the warm temperate zone and the East Asia monsoon area, the variations in the thickness of the laminae are not only related to the change in the climatic factors themselves but also related to the degree of climatic stability. In the coastal area belonging to the warm temperate zone and the East Asia monsoon area, the climate change between the LIA (Little Ice Age) and the MWP (Medieval Warm Period), in addition to less precipitation and low temperatures (a type of dry and cold climate), also shows an obviously decreasing trend in the degree of climatic stability.