Reactive iron as an important reservoir of marine organic carbon over geological timescales

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Yunru Chen, Liang Dong, Weikang Sui, Mingyang Niu, Xingqian Cui, Kai-Uwe Hinrichs, Fengping Wang


Reactive iron (FeR) has been suggested to serve as a semi-persistent sink of organic carbon (OC) in surface marine sediments, where approximately 10-20% of total OC (TOC) is associated with FeR (FeR-OC). However, the persistence of FeR-OC on geological timescales remains poorly constrained. Here, we retrieved FeR-OC records in two long sediment cores of the northern South China Sea spanning almost the past 100 kyrs. Most prominently, the downcore marine-sourced FeR-OC contributes a relatively stable proportion of 13.3±3.2% to TOC. However, distinctly lower values of less than 5% of TOC, accompanied by notable 13C depletion of FeR-OC are observed in the sulfate-methane transition zone (SMTZ), where active sulfate reduction and potential iron reduction are indicated by microbial composition and geochemical modelling. FeR-OC is suggested to be remobilized by microbially mediated reductive dissolution of FeR (and might be substituted with freshly formed 13C-depleted OC). The global budget of FeR-OC in microbially active Quaternary marine sediments could be as large as 219±133×10^17 g, which is 18-48 times the size of the atmospheric carbon pool. Thus, sedimentary FeR-OC as an exchangeable reservoir of labile OC may support deep life and play a role in regulating Earth’s carbon cycle over geological timescales.



Biogeochemistry, Earth Sciences, Environmental Microbiology and Microbial Ecology Life Sciences, Microbiology


iron oxides, Organic carbon preservation, marine sediments, early diagenesis


Published: 2023-09-20 08:14

Last Updated: 2023-09-20 12:14


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Conflict of interest statement:
The authors declare no competing interests.

Data Availability (Reason not available):
Raw Illumina sequence data of the 16S rRNA gene generated for cores QDN-14B and QDN-G1 in this study has been deposited in the NODE (the National Omics Data Encyclopedia, database under the project number OEP004264 and OEP004265, respectively. All other data discussed in the paper are available in the Source Data.

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