Development and Intercomparison of Methodologies to Measure Dissolved Ferrous Iron in Seawater

微量金属铁是整个海洋中的一种关键微量营养素，在调节初级生产方面发挥着重要作用。铁（化学符号Fe）可以以不同的电离状态存在于环境中，主要是还原形式的Fe（II）和氧化形式的Fe（III），这会影响其在水柱中的化学行为，并最终影响研究人员准确测量其丰度的能力。化学海洋学界迫切需要准确测量水体中的Fe（II），因为目前使用的方法可能会高估从某些深度收集的水样中的浓度。在这项研究中，南加州大学的研究人员将重新开发一种未被充分利用的方法来测量Fe（II），并在两种方法之间进行评估和比较。这项工作将使估计的Fe（II）浓度的细化，目前一个强大的方法，供未来使用，并澄清条件，目前的方法可以有效地使用。该项目将涉及强大的本科生研究机会，该研究将与来自印度的国际研究人员合作进行。Fe（II）在海水中存在氧或硝酸盐时是化学不稳定的，但它的存在已被报道在表面沃茨和氧最小区。对Fe（II）测量的严格评估很重要，因为它的化学和生物利用度与Fe（III）非常不同。Fe（II）形成弱络合物，弱水解，在海水中高度溶解。Fe（III）形成强络合物，微溶且强烈水解。在铁限制条件下，即使是少量的铁作为Fe（II）的存在也可以提高生物利用度。在纳摩尔至亚纳摩尔水平测定Fe（II）的最广泛使用的方法涉及Fe（II）催化的鲁米诺氧化，这是一种荧光（CL）反应。这种方法存在潜在的人为因素，特别是在透光层，其他减少的物种可能会干扰。研究人员将开发一种新的，修改后的版本的已发表的替代方法，以CL涉及的预浓缩的Fe（II）络合的合成螯合剂。虽然这种替代方法容易产生伪影和污染，限制了其在公海中的价值，但新方法为独立于鲁米诺方法的准确和灵敏的协议创造了一条合理的路径。在新方法开发之后，该项目将与CL方法进行相互比较，比较将在实验室、缺氧围隔生态系统、加州海岸外的沿海时间序列站和热带北太平洋东部进行。

The trace metal iron is a key micronutrient throughout the oceans that plays an important role in regulating primary production. Iron (chemical symbol Fe) can exist in different ionization states in the environment, primarily as the reduced form Fe(II) and the oxidized form Fe(III), which impacts its chemical behavior within the water column, and ultimately the ability of researchers to accurately measure its abundance. There is an urgent need in the chemical oceanography community for accurate measurements of Fe(II) in the water column, as currently used methods may overestimate concentrations in water samples collected from certain depths. In this study, researchers from the University of Southern California will significantly redevelop an underutilized methodology to measure Fe(II), and carry out an evaluation and inter-comparison between the two methodologies. This work will enable the refinement of estimates of Fe(II) concentration, present a robust methodology for future use, and clarify conditions where the current methodology can be used effectively. This project will involve strong undergraduate research opportunities, and the research will be conducted in collaboration with an international researcher from India.Fe(II) is thermodynamically unstable in seawater in the presence of oxygen or nitrate, yet its presence has been reported both in surface waters and in oxygen minimum zones. A rigorous assessment of Fe(II) measurements is important because its chemistry and bioavailability are so different than Fe(III). Fe(II) forms weak complexes, is weakly hydrolyzed and highly soluble in seawater. Fe(III) forms strong complexes, is sparingly soluble and strongly hydrolyzed. The presence of even a modest fraction of Fe as Fe(II) under Fe-limited conditions could increase bioavailability by orders of magnitude. The most widely used methodology to determine Fe(II) at nanomolar to sub-nanomolar levels involves the Fe(II) catalyzed oxidation of luminol, a chemiluminescent (CL) reaction. There are potential artifacts with this methodology, especially in the euphotic zone, where other reduced species might interfere. Researchers will develop a new, modified version of a published alternative method to CL involving the preconcentration of Fe(II) complexed by a synthetic chelator. While this alternative method is prone to artifacts and contamination that has limited its value in the open ocean, new approaches create a plausible path to an accurate and sensitive protocol that is independent of the luminol method. Following the new method development, this project will implement inter-comparisons with the CL approach, which will be conducted in the laboratory, in an anoxic mesocosm system, at a coastal time-series station off the California coast, and in the Eastern Tropical North Pacific.