Civil & Environmental Engineering, Duke University, Box 90287, Durham, NC 27708, USA.
Geochem Trans. 2008 May 19;9:6. doi: 10.1186/1467-4866-9-6.
The speciation of dissolved sulfide in the water immediately surrounding deep-ocean hydrothermal vents is critical to chemoautotrophic organisms that are the primary producers of these ecosystems. The objective of this research was to identify the role of Zn and Fe for controlling the speciation of sulfide in the hydrothermal vent fields at the Eastern Lau Spreading Center (ELSC) in the southern Pacific Ocean. Compared to other well-studied hydrothermal systems in the Pacific, the ELSC is notable for unique ridge characteristics and gradients over short distances along the north-south ridge axis.
In June 2005, diffuse-flow (< 50 degrees C) and high-temperature (> 250 degrees C) vent fluids were collected from four field sites along the ELSC ridge axis. Total and filtered Zn and Fe concentrations were quantified in the vent fluid samples using voltammetric and spectrometric analyses. The results indicated north-to-south variability in vent fluid composition. In the high temperature vent fluids, the ratio of total Fe to total Zn varied from 39 at Kilo Moana, the most northern site, to less than 7 at the other three sites. The concentrations of total Zn, Fe, and acid-volatile sulfide indicated that oversaturation and precipitation of sphalerite (ZnS(s)) and pyrite (FeS2(s)) were possible during cooling of the vent fluids as they mixed with the surrounding seawater. In contrast, most samples were undersaturated with respect to mackinawite (FeS(s)). The reactivity of Zn(II) in the filtered samples was tested by adding Cu(II) to the samples to induce metal-exchange reactions. In a portion of the samples, the concentration of labile Zn2+ increased after the addition of Cu(II), indicating the presence of strongly-bound Zn(II) species such as ZnS clusters and nanoparticles.
Results of this study suggest that Zn is important to sulfide speciation at ELSC vent habitats, particularly at the southern sites where Zn concentrations increase relative to Fe. As the hydrothermal fluids mix with the ambient seawater, Zn-sulfide clusters and nanoparticles are likely preventing sulfide oxidation by O2 and reducing bioavailability of S(-II) to organisms.
立即在深海热液喷口周围水中溶解的硫化物的形态对于化能自养生物至关重要，这些生物是这些生态系统的主要生产者。本研究的目的是确定 Zn 和 Fe 在控制南太平洋东劳扩张中心（ELSC）热液喷口场中硫化物形态方面的作用。与太平洋中其他研究充分的热液系统相比，ELSC 的特点是在沿南北脊轴的短距离内具有独特的脊特征和梯度。
2005 年 6 月，从 ELSC 脊轴沿线的四个野外地点采集了漫流（<50°C）和高温（>250°C）的喷口流体。使用伏安法和光谱法分析定量测定了喷口流体样品中的总和过滤 Zn 和 Fe 浓度。结果表明，喷口流体组成存在从北到南的变化。在高温喷口流体中，总 Fe 与总 Zn 的比值从最北部的基洛莫纳（Kilo Moana）的 39 变化到其他三个地点的不到 7。总 Zn、Fe 和可挥发酸的浓度表明，当喷口流体与周围海水混合时，由于冷却，闪锌矿（ZnS(s)）和黄铁矿（FeS2(s)）的过饱和和沉淀是可能的。相比之下，大多数样品相对于磁黄铁矿（FeS(s)）是不饱和的。通过向样品中添加 Cu(II)来测试过滤样品中 Zn(II)的反应性，以诱导金属交换反应。在部分样品中，添加 Cu(II)后可溶 Zn2+的浓度增加，表明存在强结合的 Zn(II)物种，如 ZnS 簇和纳米颗粒。
本研究结果表明，Zn 在 ELSC 喷口生境中的硫化物形态中很重要，特别是在 Zn 浓度相对于 Fe 增加的南部站点。随着热液流体与环境海水混合，Zn-硫化物簇和纳米颗粒可能会阻止 O2 氧化硫化物，并降低 S(-II)对生物的生物利用度。
