Emily H Hollingsworth, Robert B Sparkes, Jean M Self-Trail, Gavin L Foster, Gordon N Inglis

The Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) is a hyperthermal event associated with the rapid input of carbon into the ocean-atmosphere system. The oxidation of petrogenic organic carbon (OCpetro) may have released additional carbon dioxide (CO2), thereby prolonging the PETM. However, proxy-based estimates of OCpetro oxidation are unavailable due to the lack of suitable techniques. Raman spectroscopy is used to evaluate OCpetro oxidation in modern settings. For the first time, we explore whether Raman spectroscopy can evaluate OCpetro oxidation during the PETM. In the mid-Atlantic Coastal Plain, there is a shift from disordered to graphitised carbon. This is consistent with enhanced oxidation of disordered OCpetro and intensified physical erosion. In the Arctic Ocean, the distribution of graphitised carbon vs. disordered carbon does not change, suggesting limited variability in weathering intensity. Overall, this study provides the first evidence of increased OCpetro oxidation during the PETM, although it was likely not globally uniform. Our work also highlights the utility of Raman spectroscopy as a novel tool to reconstruct OCpetro oxidation in the past.