Processes Controlling the Release of Iron from Continental Margin Sediments

铁是一种限制性营养物质，人们普遍认为大气和大陆边缘沉积物是海洋铁的主要来源。有趣的是，大多数研究都集中在水柱中铁的分布和形态上。沉积物中铁的通量只被很少地测量过，而且只在上升流区测量过，因为这些环境可能为地表水提供铁的来源。为了确定沉积物中的铁通量是否对初级生产力具有重要影响，可能与大气输入相媲美，必须证明铁通量来自各种大陆边缘沉积物，包括上升流不明显的地区。在这项研究中，佐治亚理工学院的研究人员将测试三个假设，以确定来自大陆边缘沉积物的铁通量是否显著：(1)在上升流不重要的大陆边缘沉积物-水界面产生了显著的铁浓度。(2)可溶性有机铁（III）配合物是铁助熔剂中最重要的部分。(3)铁通量受沉积物有机质含量和生物扰动强度的间接调节，生物扰动控制着铁和硫酸盐还原的程度。为了验证这些假设，将使用原位测量和最先进的伏安技术，对卡罗莱纳沉积中心沉积物中有机含量和生物扰动强度的梯度进行定量分析，分析溶解铁（III）的通量和形态。此外，调节铁通量通过沉积物-水界面的生物地球化学过程将通过原位测量和沉积物孵育来确定。本研究将评估大陆边缘沉积物在上升流不明显的地区暴露于完全含氧水域中的铁通量的重要性。在不同有机成分和生物扰动强度的沉积物中研究这些过程，将揭示什么样的地球化学条件会诱发铁通量。更广泛的影响：这项研究将有可能改变基本的模式，即上升流和低氧水平需要向上覆水域产生铁通量，并确定大陆边缘沉积物是否应被视为铁的重要来源，可能与大气输入相媲美，为开阔海洋的初级生产力提供燃料。该研究还将扩展我们之前的工作，并以相对较低的成本为大多数终端电子受体和减少代谢物的自主深海原位分析提供能力。这种仪器结构紧凑，适用于任何底栖着陆器，因此可以在巡游中部署在深海沉积物中。原位测量成为海洋学研究的必要组成部分，两名博士生将在最先进的伏安技术、原位部署和动力学建模方面发展专业知识。最后，该项目将有一个重要的教育组成部分，努力将本科工程师和科学家整合到海洋学研究中，每年夏天为教师提供研究经验，让她有机会将新的视角带入课堂，并继续每年带20名学生到海上。

Iron is a limiting nutrient, and it is generally accepted that the atmosphere and continental margin sediments are the main source of iron to the oceans. Interestingly, most investigations have focused on the distribution and speciation of iron in the water column. The flux of iron from sediments has only been sparsely measured and only in upwelling zones because of the likelihood that these environments provide a source of iron to surface waters. To establish whether the flux of iron from sediments has important implications for primary productivity, possibly rivalling atmospheric inputs, it is necessary to demonstrate that a flux of iron occurs from a variety of continental margin sediments, including in areas where upwelling is not significant. In this study, researchers at the Georgia Institute of Technology will test three hypotheses to determine whether the flux of iron from continental margin sediments is significant: (1) A significant concentration of iron is produced at the sediment-water interface of continental margins where upwelling is not important. (2) Soluble organic Fe(III) complexes constitute the most important fraction of the iron flux. (3) The flux of iron is indirectly regulated by the organic matter content of the sediment and the intensity of bioturbation which control the extent of iron and sulfate reduction. To test these hypotheses, the flux and speciation of dissolved Fe(III) will be quantified across a gradient in organic content and bioturbation intensity in the sediments of the Carolina depocenter using in situ measurements and state-of-the-art voltammetric techniques. In addition, the biogeochemical processes regulating the flux of iron across the sediment-water interface will be determined using in situ measurements and sediment incubations. This study will assess the importance of the iron flux from continental margin sediments exposed to fully oxygenated waters in zones where upwelling is not significant. Studying these processes in sediments of different organic composition and bioturbation intensity will demonstrate what geochemical conditions induce a flux of iron. Broader Impacts: This study will potentially modify the underlying paradigm that upwelling and low oxygen levels are required to generate an iron flux to the overlying waters and establish whether continental margin sediments should be considered an important source of iron, possibly rivaling atmospheric inputs to fuel primary productivity in the open ocean. This study will also expand our previous work and provide capability for autonomous deep-sea in situ profiling of most terminal electron acceptors and reduced metabolites at a relatively low cost. This instrumentation will be compact and adaptable to any benthic lander, such that deployments in deep-sea sediments on cruises of opportunities could be performed. In situ measurements become a necessary component of oceanographic research, and two Ph.D. students will develop expertise in state-of-the-art voltammetric technology, in situ deployments, and kinetic modeling. Finally, this project will have an important educational component with efforts to integrate undergraduate engineers and scientists in oceanographic research, provide research experience to a teacher every summer and give her the opportunity to bring a new prospective into the classroom, and continue taking up to 20 students to sea each year.