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Abstract
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.
DOI
https://doi.org/10.31223/X5437B
Subjects
Biogeochemistry, Earth Sciences, Environmental Microbiology and Microbial Ecology Life Sciences, Microbiology
Keywords
iron oxides, Organic carbon preservation, marine sediments, early diagenesis
Dates
Published: 2023-09-20 01:14
Last Updated: 2023-09-20 05:14
License
CC-By Attribution-NonCommercial-NoDerivatives 4.0 International
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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, https://www.biosino.org/node/) 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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