13C18O clumping in speleothems: Observations from natural caves and precipitation experiments

摘要: The oxygen isotope composition of speleothems is an important proxy continental paleoenvironments, because its sensitivity to variations in cave temperature and drip water δ^(18)O. Interpreting speleothem δ^(18)O records terms absolute paleotemperatures values paleo-precipitation requires quantitative separation the effects these two parameters, correcting for possible kinetic fractionation associated with precipitation calcite out thermodynamic equilibrium. Carbonate clumped-isotope thermometry, based on measurements Δ_47 (a geochemical variable reflecting statistical overabundance ^(13)C^(18)O bonds CO_2 evolved from phosphoric acid digestion carbonate minerals), potentially provides a method paleotemperature reconstructions independent composition. Application this new technique karst currently limited by scarcity published studies modern speleothems. only stalagmite reported so far literature yielded lower value than expected equilibrium precipitation, possibly due fractionation. Here we report measured natural various settings, produced experiments, synthetic analogs precipitated controlled laboratory conditions designed mimic processes. All samples yield heavier predicted experimental calibrations inorganic calcite. amplitudes isotopic disequilibria vary between samples, but there clear correlation amount disequilibrium that Even pool carbonates believed offer excellent display out-of-equilibrium values, probably inherited prior degassing within system. In addition observations, analyses flowstone Villars (France) evidence affecting single can experience large at time scales 10 kyr. thermometry calls improved physical understanding DIC processes waters, resolution issues regarding calibration carbonates.