Understanding the role of organic carbon in marine sediments is crucial for comprehending the long-term carbon cycling processes on our planet. Scientists have long been intrigued by how this organic carbon, particularly when bonded with reactive iron oxides, influences global atmospheric conditions. Recent research led by a collaborative team including Prof. Fengping Wang from Shanghai Jiao Tong University and Prof. Kai-Uwe Hinrichs of MARUM—Center for Marine Environmental Sciences—has advanced our knowledge in this area by focusing on the dynamics of iron-bound organic carbon (FeR-OC) located in subseafloor sediments, as reported in the journal Nature Communications.
Recent findings suggest that approximately 20% of organic carbon in marine sediments is associated with reactive iron oxides. This raises important questions about the fate of FeR-OC in subseafloor environments, particularly its interactions with microorganisms. While the ocean’s sediments serve as a significant carbon reservoir, the specific mechanisms governing the degradation and availability of FeR-OC have remained elusive until now. By examining sediment cores from the northern South China Sea, the research team aimed to elucidate the relationships between microbial activity and the cycling of FeR-OC within various biogeochemical zones, particularly the sulfate-methane transition zone (SMTZ).
The research indicated that in the SMTZ, with its heightened microbial activity, FeR-OC is not merely stable but dynamically remobilized through microbial processes that reduce iron oxides. This indicates that FeR-OC does not remain static in sediments over geological timescales; instead, it is subject to cycles of remineralization by microorganisms. This process produces energy that sustains a significant portion of the microbial community within this one-meter-thick SMTZ. Outside the SMTZ, however, FeR-OC appears to have a higher stability against degradation, storing a greater amount of organic carbon over long durations.
Dr. Yunru Chen, the first author of the study, pointed out that the estimated size of the global reservoir of FeR-OC in active Quaternary marine sediments could be astonishingly larger than previously thought—up to 45 times the current atmospheric carbon pool. This revelation reshapes our understanding of how organic carbon dynamics within marine sediments can influence global carbon storage and greenhouse gas concentrations.
This groundbreaking research enhances our comprehension of how FeR-OC behaves in subseafloor environments, highlighting its significant role in carbon cycling under varying microbial conditions. As these insights are integrated into ongoing projects like the Ocean Floor Cluster of Excellence at MARUM, they will undoubtedly pave the way for further investigations into marine sediments’ intrinsic functions in Earth’s carbon cycle. This study not only enriches our scientific knowledge but also underscores the intricate connections between microbial ecology and global climate systems, a relationship that warrants closer inspection in future research endeavors.
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