Collaborative Research: Transformations of soluble Mn(III) along horizontal and vertical oxygen gradients

锰（Mn）是海洋生物生长的重要微量营养元素。 在过去，所有溶解在海水中的锰被认为只以一种化学形式存在：Mn（II）。 最近的研究表明，在沃茨和沉积物中，几乎没有氧气，锰（III）可以是溶解锰的主要形式，甚至可以存在于含氧的水，如果连接到特定的有机分子称为配体。这项研究将进一步研究这些发现，旨在量化负责Mn（III）在不同氧浓度下循环的化学和微生物过程。该研究将比较布罗德基尔河湿地，切萨皮克湾和下圣劳伦斯河口的实地考察;测量已知具有强氧梯度和不同有机碳源的水柱和沉积物，这些有机碳源可以改变配体的可用性和结合强度，从而稳定溶解的Mn（III）。在某些化学形式中，锰倾向于像铁一样起作用，因此这项研究可能会通过帮助海洋化学家更多地了解类似氧梯度中的铁循环而产生更广泛的影响。随着人们对海洋中氧浓度降低（缺氧）的日益关注，特别是在沿海地区，了解Mn（III）与有机配体在氧梯度上的反应对于了解Mn对生物体的可用性可能变得重要。该项目包括支持一名研究生和两名博士后研究人员的参与和指导，并将有一个美国-加拿大合作。各种公众宣传活动的计划与K-12教师被选为参与者的研究巡航。锰（III）最近才被认为是一个重要的氧化还原态锰在海水中。以前，人们普遍认为，通过0.2或0.4 μm过滤器的所有Mn都是溶解的Mn（II），而保留的部分是固体Mn（III，IV）氧化物。 在黑海、波罗的海和切萨皮克湾的研究表明，可溶性Mn（III）可高达水柱中溶解Mn的100%。 此外，Mn（III）可以作为与有机配体的络合物存在于含氧海水中。该项目将量化和限制周围的机制弱和强锰（III）配体转换垂直和水平的氧梯度。 实地研究包括各种有机碳源和氧动力学系统：下圣劳伦斯河口，切萨皮克湾，布罗德基尔河湿地河口。这项研究将继续告知我们目前对沿海系统中锰地球化学的理解正在发生的根本转变。 结果也应该适用于涉及铁（III）配体转化的氧化还原过程，因为锰和铁往往表现出类似的氧化还原化学在类似的环境条件下。

Manganese (Mn) is an important trace nutrient for biological growth in marine organisms. In the past, all Mn dissolved in seawater was thought to exist in only one chemical form: Mn(II). Recent work in waters and sediments with little or no oxygen has shown that Mn(III) can be the dominant form of dissolved Mn and can even be present in oxygenated water if attached to specific organic molecules called ligands. This research will further investigate these discoveries, aiming to quantify the chemical and microbiological processes responsible for Mn(III) cycling under varying oxygen concentrations. The research will compare field sites in the Broadkill River wetland, the Chesapeake Bay, and the Lower St. Lawrence Estuary; measuring the water column and sediments known to have strong oxygen gradients and different organic carbon sources that could change the availability and binding strength of ligands that would stabilize dissolved Mn(III). In some chemical forms, Mn tends to act like iron, so this research may have broader implications by helping marine chemists to understand more about iron cycling in similar oxygen gradients. With growing concerns over diminished oxygen concentrations (hypoxia) in the ocean, and particularly in coastal regions, understanding the reactions of Mn(III) with organic ligands across oxygen gradients could become important for understanding Mn availability to organisms. The project includes support for the participation and mentoring of one graduate student and two postdoctoral researchers, and there will be a U.S.-Canada collaboration. A variety of public outreach activities are planned with a K-12 teacher to be selected as a participant on a research cruise.Mn(III) has only recently been recognized as an important redox state for Mn in seawater. Previously, it was widely accepted that all Mn that passes through a 0.2 or 0.4 µm filter is dissolved Mn(II) while the retained portion is solid Mn(III, IV) oxide. Research in the Black Sea, the Baltic Sea, and the Chesapeake Bay has shown that soluble Mn(III) can be up to 100% of the dissolved Mn in the water column. Also, Mn(III) can exist as complexes with organic ligands in oxygenated seawater. This project will quantify and constrain the mechanisms surrounding weak and strong Mn(III) ligand transformations across vertical and horizontal oxygen gradients. Field sites to be studied include systems with a variety of organic carbon sources and oxygen dynamics: the Lower St. Lawrence Estuary, Chesapeake Bay, and Broadkill River wetland estuary. This research will continue to inform the fundamental shift that is taking place in our current understanding of Mn biogeochemistry in coastal systems. The results should also be applicable to redox processes involving Fe(III) ligand transformations, since Mn and Fe tend to exhibit similar redox chemistry under similar environmental conditions.