THE ROLE OF INTERNAL WATER IN CARBONATE CLUMPED ISOTOPE RESETTING

Carbonate clumped isotope (Δ₄₇) can be reset at elevated temperatures either through solid-state ¹³C─¹⁸O bond reordering or oxygen exchange with internal water including structural water, fluid inclusions, and organic-associated water. Results from heating experiments for biotic and abiotic carbonates suggest internal water can facilitate carbonate clumped isotope resetting when a large fraction of carbonate exchanges with internal water. Our recent studies using first-principles simulations (Perez-Beltran et al., 2023; Sun et al., in review) reveal that the lattice-bound water molecule greatly reduces the free energy of activation (ΔA^‡) for solid-state oxygen exchange in both trigonal and orthorhombic carbonate crystal lattices. For example, the presence of a water molecule in the calcite structure reduces the ΔA^‡ by ~40%. To correctly apply the reordering kinetics to thermal history and sample preservation studies, it is therefore critical to understand how the abundance and form of internal water of carbonates affect the overprinting on the reordering kinetics. Here, we compare the carbonate clumped isotope resetting for materials with different internal water contents. A high-temperature elemental analyzer (TC/EA)-isotope ratio mass spectrometer (IRMS) system is employed to measure the abundance of internal water for original and heated materials to examine the corresponding dehydration progress. Based on measured water contents and isotopic compositions, we propose mechanisms to explain the kinetic link between thermally induced dehydration, evolution of carbonate δ¹⁸O, and Δ₄₇ resetting.