Abstract We investigated the speciation of Fe and distributions of Fe-binding ligands in the hydrothermal plumes over high- and low-temperature vents and over diffuse venting fields above the Mariana back-arc spreading center. The concentrations of ligands ([L]) and conditional stability constants (K’FeL) of the natural Fe ligand pool were measured by a reverse titration-competitive ligand exchange-adsorption cathodic stripping voltammetry (RT-CLE-ACSV). The results showed that the buoyant and non-buoyant plume samples over the low-temperature Burke had the highest dissolved Fe/total Fe (DFe/TFe) of 82.2 ± 8.8% and labile Fe/total Fe (FeLab/TFe) of 43.3 ± 5.6%. In contrast, in the plume samples above the high-temperature Perseverance field, TFe had the lowest proportions of DFe (48.8 ± 12.2%) and FeLab (19.4 ± 8.8%). The linear relationships between Fe species and total Mn (TMn) in the buoyant plume over Burke suggest a simple conservative mixing with ambient seawater, which resulted in constant values of DFe/TFe. However, in the non-buoyant plume over Burke, DFe/TFe decreased with plume dilution. The plume samples sourced from the diffuse flow over newly erupted lava had the highest proportion of DFe present as FeLab (74.6 ± 4.0%). The [L] in the buoyant plumes over low-temperature Burke vent were up to 113.6 nM, and the logK’FeL decreased with increasing DFe and [L], suggesting the importance of weaker ligands in stabilizing Fe. For all the plume samples, the organically complexed Fe (FeL) constituted significant proportions of the DFe (29.0 ± 9.3%) and FeLab (57.5 ± 15.6%) fractions. These Fe-binding ligands were likely sourced from diffuse venting fluids adjacent to the venting sites, and may be also produced by microbes within the hydrothermal plumes.

中文翻译：

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马里亚纳弧后热液羽流中铁形态和铁结合配体的特征

摘要 我们研究了马里亚纳弧后扩张中心上方高温和低温喷口以及扩散喷口场上的热液羽流中 Fe 的形态和 Fe 结合配体的分布。通过反向滴定-竞争性配体交换-吸附阴极溶出伏安法 (RT-CLE-ACSV) 测量天然 Fe 配体池的配体浓度 ([L]) 和条件稳定性常数 (K'FeL)。结果表明，低温伯克上的浮力和非浮力羽流样品的溶解铁/总铁（DFe/TFe）最高，为 82.2±8.8%，不稳定铁/总铁（FeLab/TFe）为 43.3± 5.6%。相比之下，在高温 Perseverance 场上方的羽流样本中，TFe 的 DFe (48.8 ± 12.2%) 和 FeLab (19.4 ± 8.8%) 的比例最低。伯克上空的浮力羽流中 Fe 种类与总 Mn (TMn) 之间的线性关系表明与周围海水进行了简单的保守混合，从而导致 DFe/TFe 的恒定值。然而，在 Burke 上空的非漂浮羽流中，DFe/TFe 随羽流稀释而降低。来自新喷发熔岩上的扩散流的羽流样本中 DFe 的比例最高，为 FeLab (74.6 ± 4.0%)。低温伯克喷口上方的浮力羽流中的 [L] 高达 113.6 nM，并且 logK'FeL 随着 DFe 和 [L] 的增加而降低，表明较弱的配体在稳定 Fe 方面的重要性。对于所有羽流样品，有机络合的 Fe (FeL) 构成了 DFe (29.0 ± 9.3%) 和 FeLab (57.5 ± 15.6%) 部分的重要比例。