Study examines dynamic role of iron oxides in the preservation of organic carbon in the seafloor
Yunru Chen sets up incubation vessels in the laboratory to further investigate the interactions between iron minerals, organic matter and microorganisms in marine deposits. Image credit: MARUM – Center for Marine Environmental Sciences, University of Bremen; Y. Chen
The preservation of organic carbon in marine deposits has long been a key unanswered question for understanding the long-term carbon cycle on Earth.
A collaboration between the research group of Prof. Fengping Wang at Shanghai Jiao Tong University and Prof. Kai-Uwe Hinrichs at MARUM – Center for Marine Environmental Sciences and the Department of Geosciences at the University of Bremen has recently gained new insights into the dynamic cycling of iron-bound organic carbon in subseafloor sediments, which are found in Nature communication.
On geological time scales, the rate of deposition of organic carbon in sediments exerts a major influence on the concentrations of oxygen and carbon dioxide in the atmosphere, thereby significantly affecting the environmental conditions of the Earth. In marine deposits, about 20% of the organic carbon is directly bound to reactive iron oxides (FeR).
However, the fate of reactive iron-bound organic carbon (FeR-OC) in subseafloor sediments and its availability to microorganisms remain unclear.
To investigate this, the team reconstructed continuous FeR-OC records in two sediment cores from the northern South China Sea, spanning the suboxic to methanic biogeochemical zones and reaching a maximum age of about 100,000 years.
The study shows that in the sulfate-methane transition zone (SMTZ) with high microbial activity, FeR-OC is remobilized during microbially mediated iron reduction processes and subsequently remineralized by microorganisms. The energy generated can support a significant portion of the microbial life in the approximately one meter thick SMTZ.
With the exception of the SMTZ, a relatively stable fraction of total organic carbon survives microbial degradation processes as FeR-OC and is stored in marine deposits over geological time.
Dr. Yunru Chen, lead author of the study, says: “This means that the estimated global reservoir of FeR-OC in microbially active Quaternary marine deposits could be 18 to 45 times larger than the atmospheric carbon pool.”
This study makes a crucial contribution to assessing the stability of sedimentary FeR-OC in response to post-depositional microbial activities and provides insight into their dynamic cycling and persistence in subseafloor sediments. The results will feed into the Cluster of Excellence Ocean Floor, which is coordinated at MARUM.
Further information:
Yunru Chen et al., Cycling and persistence of iron-bound organic carbon in subseafloor sediments, Nature communication (2024). DOI: 10.1038/s41467-024-50578-5
Provided by the Center for Marine Environmental Sciences at the University of Bremen
Quote: Study explores dynamic role of iron oxides in preserving seafloor organic carbon (August 19, 2024), accessed August 19, 2024 from https://phys.org/news/2024-08-explores-dynamic-role-iron-oxides.html
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