Role of reactive iron in the preservation of organic carbon in marine sediments
Carbon sink of marine sediments is an important part of blue carbon and understanding the carbon storage mechanism of sediments is of great significance to reveal the relationship between climate change and global carbon cycle.The protective effect of minerals on organic carbon is considered to be the most important stabilizing mechanism,among which iron minerals play an important role in capturing organic carbon and forming"rust sink"during the accumulation of organic carbon in sediments.Recent researches on the carbon storage by reactive iron in marine sediments were systematically reviewed and the extraction methods,reactive iron types,carbon sequestration amount/mechanism,organic matter sources and molecular types binded by reactive iron were summarized to deepen the understanding of the interaction between minerals and organic carbon.Reactive iron in marine sediments is ex-tracted by the reduction of disulfite-bicarbonate-citrate(CBD),mainly in the form of goethite,ferrihydrite and hematite.Reactive iron can bind up to about 80％of organic carbon in marine sediments,and the binding mecha-nisms include adsorption dominated by ligand-exchange and coprecipitation/chelation.Reactive iron and organic carbon are combined by adsorption mechanisms when the FeR-OC:Fe molar ratio is lower than 1.00,otherwise combined by coprecipitation,which has higher organic matter binding capacity and stability than adsorption.Reac-tive iron is preferentially combined with marine compounds in most of the marine sediments,but preferentially com-bined with terrestrial compounds in the estuarine and delta areas where redox is frequent.Molecular simulation ex-periments,lignin oxidation degradation and X-ray near-edge absorption spectra showed that reactive iron combined preferentially with aromatic carbon and carboxyl carbon.Reactive iron plays an important role in the preservation of organic matter and mitigating the negative feedback caused by climate change.It is suggested that the binding process of soluble organic matter with iron minerals and the quantitative/comparative study of the importance of dif-ferent mechanism should be evaluated in future studies.
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维普
