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，但它在海洋中被极大地稀释了。缺乏铁的地表水限制了被称为浮游植物的微观海洋生物的生长，以及它们从大气和海洋表面去除碳的能力。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。最近的数据显示，深海温泉，也被称为热液喷口，影响全球铁预算，对地表铁供应很重要。全球沿着火山扩张中心发现了热液喷口，在那里通过构造活动形成了新的海底。新的多孔海床允许海水在热的、化学反应的岩石中循环，形成热液流体。这些流体的密度较低（温度为300-400°C），低于深海水（2°C），因此流出喷口的水在与周围海水混合时上升，最终形成热液羽流。这些富含营养的羽状物可以延伸10-1000公里进入海洋内部。为了解释热液铁进入海洋内部的远程运输，模型表明需要稳定剂（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普遍。研究这些机制的热液铁稳定在不同的喷口系统将提供深入了解本地和长期铁利用的深海海洋微生物和浮游植物在海洋表面。在这个项目中，将研究来自四个不同火山扩张中心的热液柱中铁结合有机配体的来源、浓度和特征，以了解它们对铁稳定和向海洋内部运输的影响。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热液衍生的溶解铁在各种热液喷口系统中的中性浮力羽流的远端运输(2)研究热液系统中的微生物是否负责这些强有机配体（即铁载体）的产生。这项工作将使用现有样本和将在即将到来的实地考察中收集的机会样本的组合，每个样本都来自不同的传播中心。这些发现将大大提高我们对热液铁运输的理解，并有助于未来对热液铁在全球铁循环中的命运进行建模。该项目将支持培训两名早期职业科学家、一名本科生实习生和用于中学深海环境项目的STEM讲习班工具包，这些工具包将由合作开发，并通过NOAA太平洋海洋环境教育和推广网页免费提供。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.