石笋流体包裹体温度重建方法的现代过程评估

Temperature is a key indicator in paleoclimate records, and high-precision reconstructions of past temperatures are central to paleoclimate research. In East Asia, scientists often rely on geological proxies such as tree rings, ice cores, and lake sediments to study historical temperature changes. However, high-resolution absolute temperature records remain limited, and many reconstructions may be affected by seasonal biases related to growth or deposition processes. Cave monitoring studies have shown that cave temperatures closely align with local annual averages, making stalagmite fluid inclusions a promising tool for reconstructing past temperatures with reduced seasonal biases. By integrating hydrological and climatic proxies such as hydrogen and oxygen isotopes, carbon isotopes, and trace elements, stalagmite fluid inclusions offer significant potential for detailed studies of regional hydrothermal variations. To improve temperature reconstruction from fluid inclusions, it is essential to calibrate and validate methods using cave monitoring data and recently active stalagmites. This study conducted isotopic analysis of fluid inclusions in modern stalagmites from Shennong Cave (117°15′N, 28°42′E) in southeastern Jiangxi Province, China, to reconstruct temperature. We validated these findings using cave monitoring data collected from June 2022 to December 2023, aiming to confirm the methods and equations used for fluid inclusion temperature reconstruction in Chinese caves. Four actively growing calcite stalagmites (SNN2, SNN3, SNN4, and SNN5) were collected from Shennong Cave. Each stalagmite displayed dripping water and fresh deposits at the top during sampling, confirming active growth and alignment with the uranium-series dating results. The δD and δ¹⁸ O values of fluid inclusions were analyzed using a system developed by Tian et al. (2020) at Xi’an Jiaotong University, equipped with a Picarro L2140-i water isotope analyzer and a vacuum crushing device. Monitoring data revealed a long-term decline in δ¹⁸ O values of drip water, influenced by the El Niño-Southern Oscillation, whereas δ ¹⁸ O values in carbonate deposits on glass slides fluctuated seasonally. Our findings showed that during the dry season, when cave humidity was low, the actual δ¹⁸ O values in the carbonate deposits exceeded the theoretical values, suggesting that increased ventilation during this period affected δ indicated that temperature was more strongly correlated with δ¹⁸ Ofractionation. Correlation analysis indicated that temperature was more strongly correlated with δ¹⁸ O in carbonate deposits than humidity, highlighting temperature as the primary factor regulating variations in carbonate oxygen isotopes. By integrating previous fluid inclusion and isotopic studies of atmospheric precipitation and cave drip water in the Shennong Cave region, we found that isotopes in fluid inclusions and drip water were primarily aligned with the local meteoric water line. Therefore, we used a local meteoric water line equation for the temperature reconstruction. By combining isotopic values from drip water and δ¹⁸ Oin carbonate deposits with the local meteoric water line, we reconstructed intermonthly temperature variations within the cave. The reconstructed temperatures closely matched the monitored monthly averages, thereby validating the methods and equations proposed by Johnston et al. (2018). We applied this approach to reconstruct temperatures from four recent stalagmites in the Shennong Cave. The reconstructed annual mean temperatures fell within the range of seasonal variations observed in modern cave temperatures, with a 4°C difference between the Little Ice Age and post-industrial periods. This variation is consistent with the historical reconstruction of eastern China, although it has a slightly broader range. Preliminary cave monitoring data also enabled us to establish an empirical temperature calculation formula specific to Shennong Cave. Further research will incorporate additional cave monitoring and fluid inclusion isotopic data to refine this formula for broader application across the Asian monsoon region. This study provides critical technical and theoretical support for paleotemperature reconstruction using stalagmite fluid inclusions throughout the Asian monsoon region.