Carbon in karst: Investigating sources, transport mechanisms and isotopic fractionation to advance the interpretation of speleothem climate records

该项目将调查环境对洞穴沉积物碳同位素组成的控制，以完善这一古环境分析工具。碳从植被到洞穴方解石的转移是由多种过程介导的，其中许多过程知之甚少，有些迄今尚未认识到。这些过程的理解可以显着提高，虽然仔细的经验性检查的一个良好的特点岩溶设置。该项目将研究德克萨斯州中部岩溶系统多个洞穴中碳的来源、传输机制和同位素分馏。具体假设为：1）洞穴滴水中溶解无机碳的碳同位素组成受深根植物的强烈影响（C3树木）和浅根植物只有最低限度的（草和草本植物）; 2）CO2以气相和液相两种形式被输送到这些洞穴中;第三章在洞穴中沉淀的方解石与进入洞穴的水不处于C同位素平衡，造成这种不平衡的动力学同位素效应主要是通过从滴水中脱气CO2而不是方解石来实现的沉淀; 4）动力学同位素效应的大小随季节变化，可以量化，从而为古气候学提供新的应用。 最重要的影响，拟议的研究将提供一个更有用的工具，洞穴和古气候研究界。 此外，该研究将支持和培训学生，研究结果将通过德克萨斯大学奥斯汀分校的一个完善的教育计划传达给高中学生和教师。

The project will investigate the environmental controls on carbon isotopic composition of speleothem in order to refine this tool for paleo-environmental analysis. The transfer of carbon from vegetation to speleothem calcite is mediated by multiple processes, many of which are poorly understood and some heretofore unrecognized. Understanding of these processes can be significantly improved though careful empirical examination of a well-characterized karst setting. Project will study the sources, transport mechanisms and isotopic fractionation of carbon in multiple caves of the karst system in central Texas. Specific hypotheses to be tested are: 1) the carbon isotope composition of dissolved inorganic carbon in cave drip water is strongly influenced by deeply rooted plants (C3 trees) and only minimally by shallowly rooted plants (grasses and herbs;, 2) CO2 is transported into these caves in both the gas and liquid phases; 3) calcite precipitated in the caves is not in C isotope equilibrium with water entering the caves and the kinetic isotope effects responsible for this disequilibrium occurs primarily by degassing of CO2 from drip water rather than by calcite precipitation; and 4) the magnitude of kinetic isotope effects varies seasonally, can be quantified, and may thus provide new applications to paleoclimatology. The most important impact of the proposed research will be to provide a more useful tool for the speleothem and paleoclimate research community. In addition, the research will support and train students and results will be communicated to high school students and teachers through a well-established educational program at the University of Texas Austin.