1Key Laboratory of Virtual Geographic Environment, Ministry of Education, School of Geography Science, Nanjing Normal University, Nanjing 210023, China
2State Key Laboratory of Cultivation Base of Geographical Environment Evolution (Jiangsu Province), Nanjing 210023, China
3Jiangsu Center for Collaborative Innovation in Geographical Environment Resource Development and Application, Nanjing 210023, China
4Department of Marine Science and Engineering, Nanjing Normal University, Nanjing 210023, China
5Nanyang Technological University, Earth Observatory of Singapore, Singapore 639798, Singapore
The study of various proxies of stalagmites is conducive to understand the characteristics and mechanisms of monsoon climate events comprehensively. Here, we present a high-resolution and multi-proxy stalagmite record from Yongxing Cave, Central China, spanning the interval between 65 and 35 ka B.P. based on high precision U/Th dating method and multi-proxy analyses. A total of 371 subsamples were drilled for oxygen and carbon isotopic measurements along the growth axis at a spacing of 0.5-mm-diameter carbide dental burrs. The analyses were conducted using a Finnigan MAT 253 mass spectrometer linked to a Kiel Carbonate Device at the School of Geography, Nanjing Normal University. The precision is 0.06‰ for δ18O and 0.05‰ for δ13C at the 1σ level. For the gray-level measurements, the polished surface of the studied section was scanned at a resolution of 1200 dpi using an EPSON Perfection 4990 Photo Scanner. The gray level was then obtained from the image using the Environment for Visualizing Images (ENVI 4.8) software while traversing down the growth axis. The values range between 0 and 442, with a spatial resolution of 20 μm. The experimental results show that during the period of 65-40 ka B.P., the stalagmite records of gray-level, δ13C and δ18O all presented millennial to sub-millennial changes, but the amplitude of δ13C is much smaller than that of δ18O. This indicates that the local climate indicators of δ13C, gray-level and lithology also respond to the Heinrich (H) events and Dansgaard-Oeschger (DO) events, but their sensitivities to events are different. During the H4 episode (about 40-38 ka B.P.), δ13C and the gray-level of the stalagmite showed anomalous changes. The significantly positive shift of δ13C reached an amplitude of 4.5‰ during H4, which was 2-3 times than other H events, while the gray-level presented the same characteristics to that of the DO cycles. We imply that the state of soil erosion may play an important role in such correspondence during H4. When the monsoon weakened to a certain threshold, the soil cover above the permeable cave was greatly deteriorated, thus weakening and/or preventing the infiltration ability of the soil-karst system and increasing the impurity contents in the stalagmite.
Meng WANG, Shi-tao CHEN, Wan-chun HUANG, Wen-qin CAI, Qing-lin GONG, Yi-jia LIANG, Xian-feng WANG, Yong-jin WANG. The response of stalagmite gray-level and isotopes to the climatic events during the last glacial period[J]. Journal of Natural Resources, 2020, 35(12): 3064