Cycling and persistence of iron-bound organic carbon in subseafloor sediments

Yunru Chen, Liang Dong, Weikang Sui, Mingyang Niu, Xingqian Cui, Kai-Uwe Hinrichs and Fengping Wang ()
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Yunru Chen: Shanghai Jiao Tong University
Liang Dong: Shanghai Jiao Tong University
Weikang Sui: Shanghai Jiao Tong University
Mingyang Niu: Shanghai Jiao Tong University
Xingqian Cui: Shanghai Jiao Tong University
Kai-Uwe Hinrichs: University of Bremen
Fengping Wang: Shanghai Jiao Tong University

Nature Communications, 2024, vol. 15, issue 1, 1-11

Abstract: Abstract Reactive iron (FeR) serves as an important sink of organic carbon (OC) in marine surface sediments, which preserves approximately 20% of total OC (TOC) as reactive iron-bound OC (FeR-OC). However, the fate of FeR-OC in subseafloor sediments and its availability to microorganisms, remain undetermined. Here, we reconstructed continuous FeR-OC records in two sediment cores of the northern South China Sea encompassing the suboxic to methanic biogeochemical zones and reaching a maximum age of ~100 kyr. The downcore 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). FeR-OC is suggested to be remobilized by microbially mediated reductive dissolution of FeR and subsequently remineralized, the flux of which is 18–30% of the methane consumption in the SMTZ. The global reservoir of FeR-OC in microbially active Quaternary marine sediments could be 19-46 times the size of the atmospheric carbon pool. Thus, the FeR-OC pool may support subseafloor microorganisms and contribute to regulating Earth’s carbon cycle.

Date: 2024
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DOI: 10.1038/s41467-024-50578-5

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