Thermal reactivity as a global metric of organic matter persistence in the environment

Timothy Eglinton
Geological Institute, Department of Earth and Planetary Sciences, ETH Zurich, Sonneggstrasse 5, 8092, Zurich, Switzerland

Abstract

The mechanisms governing organic carbon (OC) persistence in soils and aquatic sediments, including mineral association, chemical recalcitrance, and extrinsic suppression of microbial decomposition, determine how OC stocks respond to climate and land-use change. Yet, identifying and predicting the influence of these different mechanisms at scale remains challenging. Radiocarbon (¹⁴C) provides important constraints on OC age and thus persistence, but its application is typically limited in scope. Thermal stability analysis offers a complementary approach, where the proportion thermally stable organic matter – here termed “residually oxidizable carbon” (ROC) – can be rapidly determined for solid environmental samples. Here, we present a comprehensive dataset combining ROC and bulk OC ¹⁴C measurements of a large suite of samples spanning diverse matrices, ecosystems and environments along the terrestrial-to-aquatic continuum. We observe an overall relationship in which more thermally stable OC is systematically older, demonstrating that thermal stability serves as a first-order predictor of OC persistence that transcends environmental matrices. We find that mineral association is a key driver of thermal stability and OC persistence in both soils and sediments, while the slope and strength of the ROC-¹⁴C relationship are controlled by the underlying persistence mechanisms. We suggest that ROC analyses at scale coupled with select ¹⁴C measurements provides a facile approach for diagnosis of OC vulnerabilities across terrestrial and aquatic environments, offering a stability metric for monitoring programs and Earth system models.