Reversible scavenging traps hydrothermal iron in the deep ocean
Reversible scavenging traps hydrothermal iron in the deep ocean
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DOI：
10.1016/j.epsl.2020.116297
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发表时间：
2020-07
影响因子：
5.3
通讯作者：
S. Roshan;T. DeVries;Jingfeng Wu;S. John;Thomas Weber
中科院分区：
文献类型：
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作者：
S. Roshan;T. DeVries;Jingfeng Wu;S. John;Thomas Weber
最近的研究表明，海底热液喷口可能是海洋表面铁（Fe）的重要来源，刺激浮游生物生长和生物碳输出。然而，量化热液铁对海洋表面的供应需要精确地模拟其稳定和去除过程，而这一过程鲜为人知。在这里，我们沿着一个海洋样带确定了溶解铁的物理形态，该样带跟随一个从东太平洋隆起（EPR）发出的相干热液羽流，并在热带南太平洋向西持续4000公里。我们的观测表明，羽流在水平方向上持续存在，但在垂直方向上下降，主要由非常大的铁胶体组成。在这些观测结果的指导下，我们建立了一个新的热液铁在该地区分散的尺寸分辨机制模型，其中热液铁的稳定是通过可逆的颗粒交换过程来解释的。该模型准确地捕捉了热液铁沿该样带的横向分散、向下沉降和物理形态。另一种利用热液来源的铁结合配体来促进铁在深海中的运输的模型可以重现热液铁的远程运输，但不能重现地幔柱的垂直下降。我们的模型显示，从EPR喷出的热液铁被困在深海中，只有1%的铁能到达地表，在那里它可以刺激生物生产力。在全球范围内，3-5%的热液铁到达海洋表面，其中绝大多数来自南大洋的喷口和上涌井。基于海洋环流、地幔3 - He喷发和EPR中热液Fe: 3 - He比值的数据约束估计，我们对全球海洋表面热液Fe供应的最佳估计为0.12±0.07 Gmol yr−1。这比气溶胶尘埃沉积的铁供应量低60-70倍，但在南大洋的南极区可能具有区域性重要意义。
Recent studies suggest that seafloor hydrothermal vents could be an important source of iron (Fe) to the surface ocean, stimulating plankton growth and biological carbon export. However, quantifying the supply of hydrothermal Fe to the surface ocean requires accurately modeling its stabilization and removal processes, which are poorly known. Here, we determine the physical speciation of dissolved Fe along an oceanographic transect following a coherent hydrothermal plume that emanates from the East Pacific Rise (EPR) and persists westward over 4,000 km in the Tropical South Pacific. Our observations show that the plume persists horizontally, but descends vertically, and consists primarily of very large Fe colloids. Guided by these observations, we develop a new size-resolved mechanistic model of hydrothermal Fe dispersion in this region, in which the stabilization of hydrothermal Fe is explained by a reversible particulate exchange process. This model accurately captures the lateral dispersion, downward settling and physical speciation of hydrothermal Fe along this transect. An alternate model that uses a hydrothermal source of Fe-binding ligands to facilitate Fe transport within the deep ocean can reproduce the long-range transport of hydrothermal Fe, but does not reproduce the vertical descent of the plume. Our model shows that hydrothermal Fe vented from the EPR is trapped in the deep ocean, and only 1% of this iron ever makes it to the surface where it can stimulate biological productivity. At the global scale, 3-5% of hydrothermal Fe makes it to the surface ocean, the vast majority of which originates from Southern Ocean vents and upwells in the Southern Ocean. Our best estimate of the global supply of hydrothermal Fe to the surface ocean, based on data-constrained estimates of ocean circulation, mantle 3 He venting, and the hydrothermal Fe: 3 He ratio from the EPR, is 0.12±0.07 Gmol yr− 1. This is about 60-70 times lower than the supply of Fe from aerosol dust deposition, but could be regionally important in the Antarctic zone of the Southern Ocean.