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活性铁对海洋沉积物中有机碳的保存作用
李亢,黄华梅
0
(国家海洋局南海规划与环境研究院,广东 广州510300;中国科学院南海海洋研究所,广东 广州 510301)
摘要:
沉积物碳汇是海洋碳汇的重要组成部分,揭示沉积物的储碳机制对研究气候变化与全球碳循环的相互作用具有重要意义。矿物对有机碳的保护作用是有机碳最重要的稳定机制,其中活性铁(FeR)在沉积物有机碳的累积作用中发挥着捕获有机碳并形成“铁锈碳汇”的重要作用。本文系统梳理了近年来关于海洋沉积物中FeR的固碳的研究成果,总结了海洋沉积物中FeR的提取方式、类型、固碳量、固碳机制、结合有机质来源及分子类型,阐述了FeR固碳的重要意义,旨在加深对矿物与有机碳相互作用的理解。海洋沉积物中FeR常通过柠檬酸盐碳酸氢盐连二亚硫酸盐(CBD)还原提取,主要以针铁矿、水铁矿及赤铁矿等氧化物形式存在。FeR可以结合沉积物中约80%的有机碳,结合机制包括以配体交换为主的吸附机制和共沉淀/螯合机制。FeR与有机碳的结合机制可依据铁结合有机碳(FeROC)与FeR的摩尔比值(FeROC∶FeR)简单判定,当FeROC∶FeR低于1.00时以吸附方式结合,大于1.00时以共沉淀方式结合,且共沉淀相比吸附机制具有更高的有机碳结合量及稳定性。大部分海洋沉积物中FeR优先与海源类有机质结合,但在氧化还原频繁的河口及三角洲地区倾向与陆源类有机质结合。分子模拟实验、木质素氧化降解及近边X射线吸收精细结构光谱表明FeR与芳香碳及羧基碳等有机质具有更高的亲和性。FeR对有机质的稳定保存及减缓气候变化引起的负反馈具有重要意义,建议未来更多关注沉积物中有机质与铁矿物结合的具体过程及不同沉积环境FeR固碳的差异机制,更加关注不同结合机制的定量化及重要性对比研究。
关键词:  海洋地质学  海洋沉积物  活性铁  有机碳  固碳量  结合机制
DOI:10.3969/J.ISSN.2095-4972.20230406001
基金项目:中国海洋发展基金会(2022)(CODF-002-ZX-2021);广东省促进经济高质量发展专项资金海洋经济发展项目(粤自然资合[2023]41号);林业专项(2023):典型滨海湿地碳储量核查、增汇潜力评估及碳汇交易机制研究;林业专项(2023):海洋保护地人类活动核查、生态环境和典型生态系统监测评估
Role of reactive iron in the preservation of organic carbon in marine sediments
LI Kang,HUANG Huamei
(South China Sea Institute of Planning and Environment Research, SOA,Guangzhou 510300, China;South China Sea Institute of Oceanology, CAS, Guangzhou 510301, China)
Abstract:
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 extracted 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 mechanisms include adsorption dominated by ligand-exchange and coprecipitation/chelation. Reactive iron and organic carbon are combined by adsorption mechanisms when the FeROC∶Fe molar ratio is lower than 1.00, otherwise combined by coprecipitation, which has higher organic matter binding capacity and stability than adsorption. Reactive iron is preferentially combined with marine compounds in most of the marine sediments, but preferentially combined with terrestrial compounds in the estuarine and delta areas where redox is frequent. Molecular simulation experiments, 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 different mechanism should be evaluated in future studies.
Key words:  marine geology  marine sediments  reactive iron  organic carbon  carbon sequestration  binding mechanism

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