Stability of Reactive Iron‐Bound Organic Carbon During Sulfidization of Iron Oxides: Insights From Methane‐Seep Sediments

Abstract The association of organic carbon (OC) to reactive iron oxides (Fe R ), forming OC‐Fe R complexes, represents a significant OC sink in marine sediments. However, the impact of diagenetic processes, such as sulfate reduction and iron sulfide formation, on the stability of OC‐Fe R in marine sediments remains poorly understood. Here, we compare sulfidic sediments from three cores taken at methane seeps with a non‐sulfidic sediment record from a nearby site. Our results show that an overall 6.3% decrease in OC‐Fe R is associated with a 42% reduction in Fe R during the transformation from iron oxides to iron sulfides, suggesting that OC‐Fe R is resistant to sulfidization. We observed highly 13 C‐depleted OC‐Fe R in the sulfidic sediments, likely due to the interaction between OC and Fe R during anaerobic oxidation of methane. Our findings highlight the stability of OC‐Fe R in natural sulfidic sediments, offering new insights into the role of OC‐Fe R in continental margin sediments.