石笋可溶有机质14C测年及其气候和环境意义研究

石笋有机质14C测年研究有潜力解决因石笋样品U含量低和碎屑含量高而无法获得精准U系年龄的问题。然而，由于已有研究仅基于各自的方法对单一地点的样品进行测试，使得不同研究获取的结果可能有所差别，无法进行交叉对比，加之缺乏能同时获取精准U系和有机质14C年龄的理想样品，导致石笋有机质14C年龄的可靠性仍未能厘定。为此，在前期建立的石笋可溶有机质14C测试方法的基础上，本研究将对不同气候区（山西龙凤洞、陕西九仙洞、江西神农宫洞）和不同时段（早、中、晚全新世）石笋的同层子样本进行U系、可溶有机质14C和碳酸盐14C年龄测试，结合可溶有机质在喀斯特系统中的运移特点，在时空格局上对石笋可溶有机质14C年龄进行对比分析，明确其影响因素及可靠性，探明是否存在老碳混入而影响石笋有机代用指标含义的情况。本项目有望解决部分石笋在无法获取精准U系年龄时的定年问题，对于利用石笋有机代用指标重建古环境有重要意义。

The study on 14C dating of speleothem organic matter has great potential in figuring out the problem of the unavailable of accurate U-series ages due to the low U content and high debris content in stalagmite samples. However, previous studies only analyzed samples from individual study site based on their own method, so that the results might be different, hence it is unable to carry out the comparative analysis on spatial scale, and coupled with the lack of ideal samples (not only can obtain the accurate U-series ages, but also organic matter 14C age), leading to the reliability of 14C ages of speleothem organic matter is still ambiguous. In this study, on the basis of the stalagmite dissolved organic matter 14C analysis method established by our group in the early stage, we will conduct U-series, dissolved organic matter 14C and carbonate 14C dating on sub-samples from the same growth layer of stalagmites in different climate background areas (Longfeng Cave, Jiuxian Cave and Shennong Cave) and different time period (early, middle and late Holocene), and combine with the migration characteristics of dissolved organic matter in karst system, carry out the comparative analysis on spatial and temporal scales for stalagmite dissolved organic matter 14C ages to clarify its reliability and affecting factors, and to investigate whether there is a situation in which the mixing of old carbon affects the implications of the stalagmite organic proxies. This study is expected to figure out the dating problem on part of stalagmites when the accurate U-series ages are not available, as well it is of great significance for the use of stalagmite organic proxies to reconstruct paleoenvironment.