Abstract
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 δ 18O all presented millennial to sub-millennial changes, but the amplitude of δ 13C is much smaller than that of δ 18O. This indicates that the local climate indicators of δ 13C, 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.), δ 13C and the gray-level of the stalagmite showed anomalous changes. The significantly positive shift of δ 13C 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.
Keywords
abrupt climate events, Asian monsoon, gray-level analysis of stalagmite, isotope