The Cedars is an area in Northern California with a chain of highly alkaline springs resulting from CO2-charged meteorological water interacting with a peridotite body. Serpentinization resulting from this interaction at depth leads to the sequestration of various carbonate minerals into veins accompanied by a release of Ca2+ and OH- enriched water to the surface, creating an environment which promotes rapid precipitation of CaCO3 at surface springs. This environment enables us to apply the recently developed Δ47-Δ48 dual clumped isotope analysis to probe kinetic isotope effects (KIEs) and timescales of CO2 transformation in a region with the potential for geological CO2 sequestration. We analyzed CaCO3 recovered from various localities and identified significant kinetic fractionations associated with CO2 absorption in a majority of samples, characterized by enrichment in Δ47 values and depletion in Δ48 values relative to equilibrium. Surface floes exhibited the largest KIEs (ΔΔ­47: 0.163‰, ΔΔ­48: -0.761‰). Surface floe samples begin to precipitate out of solution within the first hour of CO2 absorption, and the dissolved inorganic carbon (DIC) pool requires a residence time of >100 hours to achieve isotopic equilibria. The Δ48/Δ47 slope of samples from the Cedars (-3.223±0.519; 1 SE) is within the range of published theoretical values designed to constrain CO2 hydrolysis-related kinetic fractionation (-1.724 to -8.330). The Δ47/δ18O slope (-0.009±0.001) and Δ47/δ13C slope (0.009±0.001) are roughly consistent with literature values reported from a peridotite in Oman of -0.006±0.002 and -0.005±0.002, respectively. The consistency of slopes in the multi-isotope space suggests the Δ47-Δ48 dual carbonate clumped isotope framework can be applied to study CO2-absorption processes in applied systems, including sites of interest for geological sequestration.

Most Earth surface carbonates precipitate out of isotopic equilibrium with their host solution, complicating the use of stable isotopes in paleoenvironment reconstructions. Disequilibrium can arise from exchange reactions in the DIC-H2O system as well as during crystal growth reactions in the DIC-CaCO3 system. Existing models account for kinetic isotope effects in these systems separately but the models have yet to be combined in a general framework. Here, a box model is developed for describing disequilibrium carbon, oxygen, and clumped isotope effects in the CaCO3-DIC-H2O system. The model is applied to inorganic calcite precipitation experiments where there is a known CO2 influx and CaCO3 outflux. The example provided can be adapted to other situations involving CO2 absorption (e.g., corals, foraminifera, high-pH travertines) or degassing (e.g., speleothems, low-pH travertines, cryogenic carbonates) and/or mixing with other DIC sources.