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

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

doi:10.1038/s41467-024-50578-5

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

Nat Commun. 2024 Jul 29;15(1):6370. doi: 10.1038/s41467-024-50578-5.

Authors

Yunru Chen^{1

2}, Liang Dong³, Weikang Sui³, Mingyang Niu¹, Xingqian Cui³, Kai-Uwe Hinrichs^{2

4}, Fengping Wang^{5

6

7}

Affiliations

¹ State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, China.
² MARUM-Center for Marine Environmental Sciences, University of Bremen, D-28359, Bremen, Germany.
³ Key Laboratory of Polar Ecosystem and Climate Change, Ministry of Education, and School of Oceanography, Shanghai Jiao Tong University, Shanghai, 200240, China.
⁴ Faculty of Geosciences, University of Bremen, D-28359, Bremen, Germany.
⁵ State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, China. fengpingw@sjtu.edu.cn.
⁶ Key Laboratory of Polar Ecosystem and Climate Change, Ministry of Education, and School of Oceanography, Shanghai Jiao Tong University, Shanghai, 200240, China. fengpingw@sjtu.edu.cn.
⁷ Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, 519000, China. fengpingw@sjtu.edu.cn.

Abstract

Reactive iron (Fe_R) 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 (Fe_R-OC). However, the fate of Fe_R-OC in subseafloor sediments and its availability to microorganisms, remain undetermined. Here, we reconstructed continuous Fe_R-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 Fe_R-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 Fe_R-OC, are observed in the sulfate-methane transition zone (SMTZ). Fe_R-OC is suggested to be remobilized by microbially mediated reductive dissolution of Fe_R and subsequently remineralized, the flux of which is 18-30% of the methane consumption in the SMTZ. The global reservoir of Fe_R-OC in microbially active Quaternary marine sediments could be 19-46 times the size of the atmospheric carbon pool. Thus, the Fe_R-OC pool may support subseafloor microorganisms and contribute to regulating Earth's carbon cycle.

Abstract

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