High-Resolution, Continuous Stable Carbon Isotope Analysis of Complex Organic Matter via Online Ramped Pyrolysis/Oxidation–Cavity Ring-Down Spectroscopy

Sedimentary organic carbon (OC) is an important fraction of ocean carbon sinks and spans a broad reactivity continuum across heterogeneous mixtures. Stable carbon isotope (δ13C) measurements of bulk OC are widely used for source reconstruction, but they obscure isotopic heterogeneity among mixing OC components. Here, we couple ramped pyrolysis/oxidation (RPO) with cavity ring-down spectroscopy (CRDS) to enable continuous, online δ13C measurements of CO2 evolved during thermal decomposition, providing high-resolution temperature-δ13C profiles for the concept of OC reactivity continuum. Analytical performance is evaluated via abundance-based signal thresholds, blank characterization, and δ13C calibrations with international reference materials. Furthermore, we employed this system to resolve distinct δ13C trajectories for labile, resistant, and refractory fractions of surface or core sediments in the East China Sea and Japan Trench, providing a new insight for source attribution across heterogeneous OC mixtures. The workflow can also be transferable to soils, aerosols, and other low-carbon matrices for mechanistic studies of carbon sources and stability in environmental and analytical chemistry.