Relationship between climate, environment, and anthropogenic activities in coastal North China recorded by speleothem δ¹⁸O and δ¹³C ratios in the last 1 ka

Abstract. Abstract: Stalagmite KY-1 was collected from Kaiyuan Cave, which is in the warm temperate zone and East Asia monsoon area in Shandong Peninsula, coastal Northern China. Based on the results of U-²³⁰Th-dating, continuous counting of laminae, and linear interpolation/extrapolation, we determined that the stalagmite grew over the last 1 ka between AD 892 and AD 1894. This period includes the Medieval Warm Period (MWP), Little Ice Age (LIA), and an early stage of the Current Warm Period (CWP), and corresponds to a time between the late Tang Dynasty and the late Qing Dynasty of ancient China. We collected 583 samples along the growth axis of stalagmite KY1, and selected 303 samples for δ¹⁸O and δ¹³C ratio measurements according to the Interval test principle to acquire a series of time data. The variation of the δ¹⁸O ratios suggest that a climatic mutation occurred in Shandong Peninsula around AD 1482, corresponding to the MWP/LIA transition period. The variation of these ratios is generally controlled by the variation of solar radiation. However, the variability of the δ¹⁸O ratios was less than the contemporaneous changes in solar activity in late MWP and late LIA, and more than the contemporaneous changes in solar activity between LIA; the MWP/LIA transition time lagged the contemporaneous solar activity by 30–50 yr. The δ¹³C ratios showed overall synchronization with the δ¹⁸O ratios: both were consistent with the MWP and LIA periods, and both showed the same mutation. However, the curve of the δ¹³C ratios was smoother than that of the δ¹⁸O ratios, and the variations of both were not synchronized in the late LIA. The transitions between the major dynasties in the past 1000 years of Chinese history, and the late period of Qing Dynasty coincide with the transition periods of the summer monsoon. Furthermore, the impacts of the fluctuation of the sub-climate change trend on the historical evolution of human society in MWP and LIA were more prominent than those of the violent climate transition between MWP and LIA. On the other hand, the degree of land use continually increased in the study area, which, together with the climatic change, affected the vegetation-soil-groundwater environment system in the mountainous land above the cave. The degree of impact of human land use on the mountainous vegetation, soil characteristics, and their change trends did not exceed the extent of that of climate change from AD 892–1318, but reached or exceeded small climate changes from AD 1318–1497, and reached or exceeded the sharp climate change that occurred between AD 1483–1779. The degree of impact of human land use and the environment stabilized between AD 1779–1894, and the impacts of climate change on the environment were relatively prominent.