Role of manganese in suboxic biogeochemical cycles

锰是海洋氧化还原循环的重要组成部分，因为它存在于多种氧化还原状态，并通过细菌介导的过程在这些状态之间快速循环。电子在锰种之间转移的容易性使得锰循环很容易与其他氧化还原循环耦合。在自然界中，锰以三种氧化态存在：Mn（II）、Mn（III）和Mn（IV）。其中，Mn（III）大多被忽略。不同的测量锰的方法给出了关于沉积物孔隙水中溶解锰分布的矛盾信息，这表明沉积物的亚氧部分含有两种而不是一种可溶性物质，Mn（II）和Mn（III）。Mn（III）在亚氧水和孔隙水中的存在可以解决几个重要问题。它将提供一种将溶解的Mn从沉积物转移到水柱的机制；这将为氮循环中氨被锰直接氧化成氮气的新途径提供证据。我们提议与来自两所美国大学的研究人员合作，开展一项生物地球化学和微生物学研究，分别研究产生和消耗溶解Mn（III）的性质、化学计量学和反应速率。这项研究将在圣劳伦斯河口-萨格奈峡湾环境中进行，原因如下：1)我们有近30年的沉积物和水柱中锰的数据。2)沉积物中含有高浓度的锰，锰循环是主要的成岩作用过程。3)在年代际尺度上，固相锰的分布处于稳定状态，而溶解锰的分布则不稳定。4)该系统提供了低氧和高氧底水的极好例子，可以帮助我们比较和对比端元环境。5)我们将要研究的许多科学问题都源于以前在这个系统中进行的工作。

Manganese is an important component of marine oxidation-reduction cycles because it exists in multiple redox states and is rapidly cycled between these states by bacterially mediated processes. The ease with which electrons are transferred between manganese species allows the manganese cycle to be readily coupled to other redox cycles. In nature, manganese exists in three oxidation states: Mn(II), Mn(III), and Mn(IV). Of these, Mn(III) has mostly been ignored. Different approaches to measuring manganese give contradictory information about the distribution of manganese dissolved in sediment pore waters that suggests that the suboxic part of the sediment contains not one but two soluble species, Mn(II) and Mn(III). The presence of Mn(III) in suboxic water and pore water can resolved several important issues. It would provide a mechanism for transferring dissolved Mn from sediment to water column; and it would provide evidence for a novel pathway in the nitrogen cycle whereby ammonia is oxidized directly to nitrogen gas by manganese. We propose to conduct a biogeochemical and microbiological study, in collaboration with researchers from two US universities, of the nature, stoichiometry, and rate of reactions that respectively produce and consume dissolved Mn(III). The study will be carried out in the St. Lawrence Estuary - Saguenay fjord environment for these reasons: 1)We have nearly 30 years worth of data on manganese in sediment and water column. 2) The sediments contain high concentrations of manganese, and manganese cycling is a dominant diagenetic process. 3) The solid phase manganese distribution is in steady state over decadal time scales, whereas the distribution of dissolved manganese is not. 4) The system provides excellent examples of low oxygen and high oxygen bottom waters that can help us compare and contrast end-member environments. 5) Many of the scientific questions we will investigate stem from previous work carried out in this system.