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.