Diffuse Hydrothermal Venting: A Hidden Source of Iron to the Oceans
Diffuse Hydrothermal Venting: A Hidden Source of Iron to the Oceans
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DOI：
10.3389/fmars.2019.00329
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发表时间：
2019-07
影响因子：
3.7
通讯作者：
A.J.M. Lough;D. Connelly;W. Homoky;Jeffrey A. Hawkes;V. Chavagnac;A. Castillo;M. Kazemian;K. Nakamura;T. Araki;B. Kaulich;R. Mills
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文献类型：
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作者：
A.J.M. Lough;D. Connelly;W. Homoky;Jeffrey A. Hawkes;V. Chavagnac;A. Castillo;M. Kazemian;K. Nakamura;T. Araki;B. Kaulich;R. Mills
铁 (Fe) 限制或共同限制世界大片海洋区域的初级生产力和固氮作用。深海的热液铁供应量广泛；然而，这项工作的大部分重点是检查高温、集中在山脊轴上的流动，这些流动会产生“黑烟”羽流。其他类型的喷发对全球海洋铁循环的贡献很少受到关注。为了彻底了解海洋热液铁的来源，必须比较不同类型的喷口地点。为了检查更分散、更高 pH 值的喷发源的作用，对冯达姆喷发场 (VDVF) 上方的热液羽流进行了采样，以检测总可溶性铁（未过滤，TDFe）、溶解性铁（<0.2 µm，dFe）和可溶性铁（<0.02 µm，sFe）。使用扫描电子显微镜和软 X 射线光谱显微镜对原位采样的羽流颗粒进行了表征。 VDVF 喷口排放出明显清澈的液体，颗粒铁 (TDFe-dFe) 浓度高达 196 nmol kg-1，与大西洋中脊黑烟羽羽中测量的浓度相当。随着 TDFe 浓度的降低，胶体铁 (cFe) 和 sFe 占 TDFe 的比例增加。羽流中 sFe 和 cFe 百分比的增加不能用颗粒沉降或与背景海水混合来解释。需要通过 pFe 的分解在羽流中产生新的 cFe 和 sFe 来关闭 Fe 预算。我们认为，cFe 和 sFe 的比例增加反映了通风口附近含铁有机颗粒的夹带、分解和回收。 VDVF 的铁羽流剖面与之前对“黑烟囱”喷口的研究有很大不同，在羽流中形成新的 pFe 会减少 cFe 的量。富铁胶体和颗粒的形成和去除将控制从热液系统供应到深海的 dFe 的数量和物理化学成分。这项研究强调了离轴扩散源与黑烟熏源热液铁稳定性的差异。由于检测和定位此类地点的困难，离轴扩散通风代表了海洋中潜在的重要且先前被忽视的铁源。
Iron (Fe) limits or co-limits primary productivity and nitrogen fixation in large regions of the world’s oceans. Hydrothermal supply of Fe to the deep ocean is extensive; however most of this work has focused on examining high temperature, focused flow on ridge axes that create “black smoker” plumes. The contribution of other types of venting to the global ocean Fe cycle has received little attention. To thoroughly understand hydrothermal Fe sources to the ocean, different types of vent site must be compared. To examine the role of more diffuse, higher pH sources of venting, a hydrothermal plume above the Von Damm vent field (VDVF) was sampled for Total dissolvable Fe (unfiltered, TDFe) dissolved Fe (<0.2 µm, dFe) and soluble Fe (<0.02 µm, sFe). Plume particles sampled in-situ were characterised using scanning electron microscopy and soft x-ray spectromicroscopy. The VDVF vents emit visibly clear fluids with particulate Fe (TDFe-dFe) concentrations up to 196 nmol kg-1 comparable to concentrations measured in black smoker plumes on the Mid-Atlantic Ridge. Colloidal Fe (cFe) and sFe increased as a fraction of TDFe with decreasing TDFe concentration. This increase in the percentage of sFe and cFe within the plume cannot be explained by settling of particulates or mixing with background seawater. The creation of new cFe and sFe within the plume from the breakdown of pFe is required to close the Fe budget. We suggest that the proportional increase in cFe and sFe reflects the entrainment, breakdown and recycling of Fe bearing organic particulates near the vents. Fe plume profiles from the VDVF differ significantly from previous studies of “black smoker” vents where formation of new pFe in the plume decreases the amount of cFe. Formation and removal of Fe-rich colloids and particles will control the amount and physico-chemical composition of dFe supplied to the deep ocean from hydrothermal systems. This study highlights the differences in the stabilization of hydrothermal Fe from an off-axis diffuse source compared to black smokers. Off-axis diffuse venting represent a potentially significant and previously overlooked Fe source to the ocean due to the difficulties in detecting and locating such sites.