贵州凉风洞洞穴系统锶同位素特征

The characteristics of ^(87)Sr/^(86)Sr in the Liangfeng Cave system,Guizhou,China

对贵州茂兰自然保护区内凉风洞(LFD)洞穴系统中各组分(土壤水、洞穴滴水、土壤与基岩等)锶同位素组成(^(87)Sr/^(86)Sr)的系统分析结果表明,各个组分的^(87)Sr/^(86)Sr比值差异显著。不同剖面土壤水^(87)Sr/^(86)Sr比值明显不同,但均介于大气降水平均值和土壤之间;不同滴水点间^(87)Sr/^(86)Sr比值差异也很明显,大多落在洞穴上覆土壤水和基岩之间,受渗透水在洞穴顶板中发生的水-土作用和水-岩作用强度控制。此外,凉风洞上覆原生喀斯特森林生物量及其凋落物返还量较大,以植物落叶为主形成的凋落物层以及被微生物分解形成的表层有机土成为除洞穴上覆土壤和基岩外的另一个直接阳离子源,其释放的Sr随水体快速下渗对滴水^(87)Sr/^(86)Sr比值产生了明显影响。因此,利用本研究区洞穴滴水及其次生化学沉积物^(87)Sr/^(86)Sr指标表征洞穴上覆气候环境信息时,有必要事先识别不同物源^(87)Sr/^(86)Sr比值及其相对贡献、运移路径水文地质过程等限制性因素影响。

The strontium isotopic compositions （^87Sr/^86Sr） of precipitation, soil water, drip water, soil, and other components of the Liangfeng Cave system in the Maolan virgin forest, Guizhou, China, were systemically measured and analyzed. The results indicate that there are significant differences in ^87Sr/^86Sr ratios among the different samples. The ^87Sr/^86Sr ratios in soil water from different soil profiles show considerable variations, and fall between the mean Sr isotope values for rainwater and soil. The ^87Sr/^86Sr ratios in drip water from different drip sites are also variable, with isotopic values ranging from soil water to bedrock levels, and are controlled by the water-soil and water-rock interactions along different flow paths through the unsaturated zone overlying the cave. Furthermore, because the biomass and annual litterfall in the Maolan karst virgin forest are abundant, the litterfall layers and organic soil provide direct cation sources that also affect the ^87Sr/^86Sr ratios of drip water. It is therefore feasible to use the strontium isotopic compositions of drip water and speleothems as past environment and climate indicators prior to distinguishing restrictive factors, including the material sources with different ^87Sr/^86Sr ratios and their relative contributions, and the hydro-geological processes along different flow paths through the unsaturated zone overlying the cave.