Are strong ligands and dissolved iron tightly coupled in hydrothermal systems?

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。铁是地壳中最丰富的元素之一，但在海洋中被极度稀释。贫铁的表层沃茨限制了被称为浮游植物的微小海洋生物的生长，也限制了它们从大气和表层海洋中去除碳的能力。然而，在过去的几十年里，我们对铁如何进入海洋的理解已经发生了变化。最近的数据表明，深海温泉，也称为热液喷口，影响全球铁的收支，对地表铁的供应很重要。热液喷口遍布全球，沿着火山扩张中心，那里的构造活动产生了新的海底。新的多孔海底允许海水通过热的化学反应性岩石循环，产生热液流体。这些流体的密度（300-400°C）低于深海沃茨（2°C），因此，从喷口流出的水在与周围海水混合的同时上升，最终形成热液羽流。这些营养丰富的羽流可以延伸到海洋内部10- 1000公里。 为了解释热液铁向海洋内部的远距离迁移，模型显示需要稳定剂（即有机配体）来防止铁沉淀和沉降到海底。然而，我们仍然不知道这些有机配体的来源和身份，以及它们在全球海洋的各种热液系统中有多常见。对不同喷口系统热液铁稳定化的这些机制进行调查，将有助于深入了解深海海洋微生物和表层海洋浮游植物对铁的本地和远距离利用。在这个项目中，铁结合有机配体的来源，浓度和身份的热液羽从四个不同的火山扩张中心将进行检查，以了解其对铁的稳定和运输到海洋内部的影响。本研究的主要目的是测试（1）强有机配体的浓度是否严格控制中性浮力羽流中的热液溶解铁在各种热液喷口系统中的远距离运输，以及（2）调查热液系统中的微生物是否负责产生这些强有机配体（即铁载体）。这项工作将使用现有的样本和样本的机会，将收集在即将到来的实地考察，每一个从不同的传播中心的组合。这些发现将大大提高我们对热液铁运输的理解，并有助于未来对全球铁循环中热液铁命运的建模工作。该项目将支持两名早期职业科学家的培训，一名本科实习生，以及用于中学深海环境课程的STEM研讨会套件，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Iron is one of the most abundant elements in the Earth’s crust, but it is extremely diluted in the ocean. Iron-poor surface waters limit the growth of microscopic marine life, called phytoplankton, and their ability to remove carbon from the atmosphere and surface ocean. However, over the last few decades, our understanding of how iron enters the ocean has evolved. Recent data has shown that deep-sea hot springs, also known as hydrothermal vents, impact global iron budgets and are important for surface iron supply. Hydrothermal vents are found globally along volcanic spreading centers where new seafloor is created through tectonic activity. The new porous seafloor allows seawater to circulate through the hot, chemically reactive rocks to create hydrothermal fluids. These fluids are less dense (hotter, 300-400°C) than deep ocean waters (2°C), so the water exiting the vents rises while mixing with ambient seawater, eventually forming hydrothermal plumes. These nutrient-rich plumes can extend for 10-1000s of kilometers into the ocean interior. To account for the long-range transport of hydrothermal iron into the ocean interior, models have shown that stabilizing agents (i.e. organic ligands) are needed to prevent iron from precipitating and settling to the seafloor. However, we still do not know the sources and identities of these organic ligands, as well as how common they are in various hydrothermal systems across the global ocean. Investigating these mechanism(s) for hydrothermal iron stabilization across different vent systems will provide insight into both local and long-range iron utilization by deep-sea marine microorganisms and phytoplankton in the surface ocean. In this project, the sources, concentration, and identities of iron-binding organic ligands in hydrothermal plumes from four different volcanic spreading centers will be examined to understand their impact on iron stabilization and transport into the ocean interior. The major aim of this research is to test whether (1) the concentrations of strong organic ligands tightly control the distal transport of hydrothermally derived dissolved iron in neutrally buoyant plumes across a variety of hydrothermal vent systems and (2) investigate if microbes from hydrothermal systems are responsible for production of these strong organic ligands (i.e. siderophores). This work will use a combination of existing samples and samples of opportunity that will be collected during an upcoming field expedition, each from distinct spreading centers. These findings would significantly enhance our understanding of hydrothermal iron transport and aid in future modeling efforts on the fate of hydrothermal iron in the global iron cycle. This project will support the training of two early career scientists, an undergraduate intern, and STEM workshop kits for middle school programs about deep-sea environments, which will be developed in collaboration and made freely available through the NOAA Pacific Marine Environmental Education and Outreach webpage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.