Organic carbon preservation by reactive iron oxides in South Yellow Sea sediments
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摘要: 土壤和沉积物中活性铁对有机质的吸附对有机质具有长期稳定和保存作用,从而在地质时间尺度上缓冲大气CO2浓度。本文利用连二亚硫酸钠还原性溶解提取活性铁氧化物(FeR)及与之结合的有机碳(Fe-OC),定量研究了南黄海沉积物中FeR与OC之间的结合方式以及FeR对OC的保存作用,讨论了深度增加对二者相互作用的影响。结果表明,南黄海沉积物中Fe-OC占沉积物总有机碳的份数(fFe-OC)为(13.2±7.47)%,即活性铁对OC的年吸附量为0.72 Mt,占全球边缘海沉积物TOC年埋藏通量的0.44%。Fe-OC的平均OC:Fe为4.50±2.61,表明共沉淀作用对有机质的保存起重要作用,且其比值随海源有机质含量增加而增加。Fe-OC稳定碳同位素(δ13CFe-OC)结果表明,FeR优先保存活性有机质,但这种选择性随OC:Fe增大而减弱。随深度增加,fFe-OC和δ13CFe-OC均未表现出显著变化,这与该海域沉积物中有机质活性较低、铁还原作用较弱有关。Abstract: Sorption of organic carbon (OC) on reactive iron (FeR) plays an important role in OC stabilization and preserving in sediments and soils, and thus can buffer the concentration of atmospheric CO2 on geological timescales. Based on the amount of OC associated with FeR (Fe-OC) in three cores from the South Yellow Sea determined by the dithionite reduction extraction, we quantitatively investigated the role of FeR in OC stabilization, mechanisms of OC and FeR association, and variation of Fe-OC with depth. Our results showed that Fe-OC accounted for (13.2±7.47)% of sedimentary total OC in the South Yellow Sea. This means that annually 0.72 Mt of OC buried in the sediments is sequestered by FeR, which is 0.44% of the global OC buried in the continental shelf sea annually. Molar ratios of OC to FeR (average 4.50±2.61) indicate that coprecipitation of OC with FeR plays an important role in OC stabilization, and the ratios increased with an increase in fractions of marine OC in the sediments. Stable isotopic compositions of Fe-OC (δ13CFe-OC) suggested that more labile OC is preferentially trapped by FeR, but this preferential trend decreases with an increase in OC/Fe ratio. No obvious changes in fFe-OCand δ13CFe-OC with depth were observed, which can be ascribed to low degradability of organic matter and consequently weak iron reduction.
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Key words:
- reactive iron oxides /
- organic carbon protection /
- marine sediments /
- sorption /
- South Yellow Sea
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