Geochemical characteristics, speciation and size-fractionation of iron (Fe) in two marine shallow-water hydrothermal systems, Dominica, Lesser Antilles
Geochemical characteristics, speciation and size-fractionation of iron (Fe) in two marine shallow-water hydrothermal systems, Dominica, Lesser Antilles
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DOI：
10.1016/j.chemgeo.2017.02.021
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发表时间：
2017-04
期刊：
影响因子：
3.9
通讯作者：
C. Kleint;T. Pichler;A. Koschinsky
中科院分区：
文献类型：
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作者：
C. Kleint;T. Pichler;A. Koschinsky
海洋浅水热液系统迄今在痕量金属通量和可能的稳定络合过程方面基本上被忽视，尽管它们将流体直接排放到透光层。因此，目前尚不清楚由浅喷口输入到表层沃茨中的稳定溶解金属的影响以及对世界海洋中初级生产率最高区域内生物活性微量金属的迁移和生物利用度的影响。粒级分布（胶体和可溶性）以及氧化还原形态和不稳定浓度的限制微量营养元素铁（Fe）在两个海洋浅水热液系统（香槟温泉和苏弗里埃），加勒比小安的列斯群岛岛弧，多米尼加海岸，两个不同喷口的地球化学特征表明，两者都受到大气和海水的影响，苏弗里埃的大气影响比香槟温泉强。以水杨醛肟（SA）为人工配体，采用改进的竞争配体交换-吸附阴极溶出伏安法（CLE-AdCSV）对可溶性和不稳定性铁进行了测定。我们的研究结果表明，集中在海底排放的流体，以及热液孔隙流体，尽管计算的理论氧化半衰期只有6.4分钟，高度富集在Fe（II），表明铁（II）的强络合，强到足以防止Fe（II）的氧化和沉淀。由于这些流体显示出富集的溶解有机碳（DOC）浓度，和非常低的化学不稳定Fe的分数，有机碳可能会发生络合作用，这是最近提出的也是一个因素，在深海热液非浮力plumes.Our研究结果表明，浅水热液作用关闭多米尼加海岸释放高浓度的稳定，生物可利用的Fe（II）进入透光层，影响了表层沃茨中Fe的生态地球化学循环。考虑到许多区域海洋浅水热液系统的丰富性，这种过程甚至可能在全球海洋dFe循环中发挥作用。
Marine shallow-water hydrothermal systems have so far largely been neglected with respect to trace metal fluxes and possible stabilizing complexation processes, even though they emit their fluids directly into the photic zone. The impact of stabilized dissolved metal input by shallow vents into surface waters as well as the effect on the transport and bioavailability of bioactive trace metals within the area of highest primary production rates in the world oceans is therefore, at present, mostly unknown.In this study, we investigated the concentration, size fraction distribution (colloidal and soluble) as well as redox speciation and labile concentrations of the limiting micronutrient iron (Fe) at two marine shallow-water hydrothermal systems (Champagne Hot Springs and Soufriere) off the coast of Dominica, Lesser Antilles Island Arc, Caribbean.Geochemical characterization of the two different vent sites showed that both are affected by meteoric and seawater influence, with a stronger meteoric influence at Soufriere than at Champagne Hot Springs. Measurements of soluble and labile Fe were performed using a modified competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) with salicylaldoxime (SA) as the artificial ligand. Our results show that focused fluids discharging at the seafloor, as well as hydrothermal pore fluids are, despite a calculated theoretical oxidation half-life of only 6.4 min, highly enriched in Fe(II), indicating a strong complexation of Fe(II), strong enough to prevent Fe(II) from oxidation and precipitation. Since these fluids show enriched dissolved organic carbon (DOC) concentrations, and very low fractions of chemically labile Fe, complexation may occur by organic carbon, which was recently suggested to also be a factor in stabilizing particulate Fe(II) in deep-sea hydrothermal non-buoyant plumes.Our results indicate that shallow-water hydrothermalism off the coast of Dominica releases high concentrations of stabilized, bioavailable Fe(II) into the photic zone, which influences the biogeochemical cycle of Fe in surface waters. Considering the abundance of marine shallow-water hydrothermal systems in many regions, such processes may even play a role in the global oceanic dFe cycle.