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

Authors :: Chen Y
Dong L
Sui W
Niu M
Cui X
Hinrichs KU
Wang F
Source :: Nature communications [Nat Commun] 2024 Jul 29; Vol. 15 (1), pp. 6370. Date of Electronic Publication: 2024 Jul 29.
Publication Year :: 2024
Abstract: Reactive iron (Fe <subscript>R</subscript> ) 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 <subscript>R</subscript> -OC). However, the fate of Fe <subscript>R</subscript> -OC in subseafloor sediments and its availability to microorganisms, remain undetermined. Here, we reconstructed continuous Fe <subscript>R</subscript> -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 <subscript>R</subscript> -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 <superscript>13</superscript> C depletion of Fe <subscript>R</subscript> -OC, are observed in the sulfate-methane transition zone (SMTZ). Fe <subscript>R</subscript> -OC is suggested to be remobilized by microbially mediated reductive dissolution of Fe <subscript>R</subscript> and subsequently remineralized, the flux of which is 18-30% of the methane consumption in the SMTZ. The global reservoir of Fe <subscript>R</subscript> -OC in microbially active Quaternary marine sediments could be 19-46 times the size of the atmospheric carbon pool. Thus, the Fe <subscript>R</subscript> -OC pool may support subseafloor microorganisms and contribute to regulating Earth's carbon cycle.<br /> (© 2024. The Author(s).)