Fractionation of Fe isotopes during Fe(II) oxidation by a marine photoferrotroph is controlled by the formation of organic Fe-complexes and colloidal Fe fractions
Fractionation of Fe isotopes during Fe(II) oxidation by a marine photoferrotroph is controlled by the formation of organic Fe-complexes and colloidal Fe fractions
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DOI：
10.1016/j.gca.2015.05.024
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发表时间：
2015-09
影响因子：
5
通讯作者：
E. Swanner;Wenfang S. Wu;R. Schoenberg;J. Byrne;F. Marc Michel;Yongxin Pan;A. Kappler
中科院分区：
文献类型：
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作者：
E. Swanner;Wenfang S. Wu;R. Schoenberg;J. Byrne;F. Marc Michel;Yongxin Pan;A. Kappler
人们对发现富铁沉积物中Fe（II）氧化细菌（FeOB）的矿物学、有机、形态学或同位素生物特征很感兴趣，这可能表明这些生物在富铁海水中的活动，在前寒武纪时代更常见。到目前为止，在由Fe（II）氧化代谢产生的Fe矿物中建立明确的Fe同位素特征的努力已经被大的动力学分馏所阻碍，这是由于新鲜氧化的含水Fe（III）在接近中性的pH下迅速沉淀为Fe（III）（oxyhydr）氧化物矿物。前体，并且不能清楚地与FeOB同位素形成的矿物区分开。然而，在海洋热液系统和富Fe（II）的泉水中，考虑到Fe（II）已被氧化的部分和实验确定的分馏因素，形成的矿物往往比预期的同位素轻。我们测量了铁同位素组成的水溶液（Feaq）和最终的铁矿物（Feppt）在批实验中产生的海洋Fe（II）氧化光养Rhodovulum iodosum。δ 56 Feaq数据最好用动力学分馏模型描述，而δ 56 Feppt的演化似乎受一个单独的分馏过程控制。我们认为，可溶性Fe（III），Fe（II）和Fe（III）提取的FePt可能作为中间体之间的Fe（II）氧化和Fe（III）沉淀。基于~（57）Fe穆斯堡尔谱、扩展X射线吸收精细结构（EXAFS）谱和X射线全散射，我们认为这些Fe相（统称Fe（II/III）中间体）可能由有机配体结合、吸附和/或胶体Fe（II）和Fe（III）矿物相组成，它们的同位素比最终的Fe（III）矿物产物轻。响应于由FeOB和无机配体（例如，SiO 44 −或PO 43 −），可以在许多天然的Fe（II）氧化环境中形成。我们建议，这些中间体的形成很可能发生在富含有机物的系统中，因此可能控制了Fe（II）被氧化或在地球过去的微生物存在下的系统中Fe矿物的最终同位素组成。
Much interest exists in finding mineralogical, organic, morphological, or isotopic biosignatures for Fe(II)-oxidizing bacteria (FeOB) that are retained in Fe-rich sediments, which could indicate the activity of these organisms in Fe-rich seawater, more common in the Precambrian Era. To date, the effort to establish a clear Fe isotopic signature in Fe minerals produced by Fe(II)-oxidizing metabolisms has been thwarted by the large kinetic fractionation incurred as freshly oxidized aqueous Fe(III) rapidly precipitates as Fe(III) (oxyhydr)oxide minerals at near neutral pH. The Fe(III) (oxyhydr)oxide minerals resulting from abiotic Fe(II) oxidation are isotopically heavy compared to the Fe(II) precursor and are not clearly distinguishable from minerals formed by FeOB isotopically. However, in marine hydrothermal systems and Fe(II)-rich springs the minerals formed are often isotopically lighter than expected considering the fraction of Fe(II) that has been oxidized and experimentally-determined fractionation factors. We measured the Fe isotopic composition of aqueous Fe (Feaq) and the final Fe mineral (Feppt) produced in batch experiment using the marine Fe(II)-oxidizing phototrophRhodovulum iodosum. The δ56Feaqdata are best described by a kinetic fractionation model, while the evolution of δ56Fepptappears to be controlled by a separate fractionation process. We propose that soluble Fe(III), and Fe(II) and Fe(III) extracted from the Fepptmay act as intermediates between Fe(II) oxidation and Fe(III) precipitation. Based on57Fe Mössbauer spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray total scattering, we suggests these Fe phases, collectively Fe(II/III)interm, may consist of organic-ligand bound, sorbed, and/or colloidal Fe(II) and Fe(III) mineral phases that are isotopically lighter than the final Fe(III) mineral product. Similar intermediate phases, formed in response to organic carbon produced by FeOB and inorganic ligands (e.g., SiO44−or PO43−), may form in many natural Fe(II)-oxidizing environments. We propose that the formation of these intermediates is likely to occur in organic-rich systems, and thus may have controlled the ultimate isotopic composition of Fe minerals in systems where Fe(II) was being oxidized by or in the presence of microbes in Earth’s past.