Collaborative Research: Source apportionment of iron in the marine atmosphere - application of stable iron isotopic measurements

在世界海洋的许多区域，初级生产力不受主要营养物质（氮、磷和二氧化硅）的限制，而是受微量营养物质铁（Fe）的限制。铁的一个主要来源是大气运输和气溶胶沉积到公海。气溶胶来自自然来源，如土壤和灰尘以及生物质燃烧，以及与工业过程和能源生产有关的人为排放。我们对这些来源的理解受限于我们识别铁的起源的能力。追踪气溶胶来源的机制包括使用元素比率，因为特定的来源具有特定的元素信号。铁同位素变化最近被证明是铁来源的潜在重要示踪剂。该项目由亚利桑那州立大学和北亚利桑那大学的研究人员合作，将探索使用铁同位素作为气溶胶的自然和人为来源的示踪剂，以评估它们作为铁来源对开放海洋的重要性。众所周知，铁限制了许多高营养、低叶绿素区域的初级生产，因此了解向海洋输送的铁的来源及其对海洋微生物的可利用性非常重要。此外，来自不同来源的气溶胶在海水中具有不同的大小和溶解度，因此这也影响了铁的生物利用度。对气溶胶中铁同位素的检查可以帮助解决这些问题，因为研究人员先前的研究已经证明，气溶胶中铁的同位素组成有明显的变化，这些变化来自自然和人为来源。这项研究将在一年的时间里测量在百慕大收集的气溶胶颗粒的铁同位素组成。之所以选择百慕大，是因为季节差异导致不同类型的气溶胶沉积——夏季风从东部吹来，携带撒哈拉土壤尘埃和其他气溶胶，而冬季风来自北美上空。该项目将把百慕大的结果与可能成为大西洋铁来源的关键人为和自然气溶胶材料的结果进行比较。此外，对这些气溶胶的元素分析将为铁同位素的结果提供独立的证实。尺寸分离样品的分析将提供额外的信息，并将与溶解度实验相结合，以评估可溶铁分数。更广泛的影响：这项工作的科学影响涉及更好地了解影响铁（一种重要的限制性微量营养素）对海洋和海洋微生物的来源和可用性的因素。作为拟议项目的一部分，研究人员将开展互动教育活动，向非理科生教授海洋营养物质可用性和有限性的主要概念，这将成为新课程“宜居世界”的一部分。此外，拟议的项目将支持研究生培训，并使代表性不足的群体受益。

In many regions of the world's ocean, primary productivity is not limited by the major nutrients (nitrogen, phosphorous and silica) but by the micronutrient iron (Fe). One major source of Fe is the atmospheric transport and deposition of aerosols to the open ocean. The aerosols come from natural sources, such as soils and dust and biomass burning, and from anthropogenic emissions related to industrial processes and energy generation. Our understanding of the sources is limited by our ability to identify the origin of the Fe. Mechanisms of tracing the sources of aerosols include the use of the elemental ratios as specific sources have specific elemental signals. Fe isotopic variation has recently been demonstrated to be a potentially important tracer of Fe sources. This project, a collaboration between investigators at Arizona State University and Northern Arizona University, will explore the use of Fe isotopes as a tracer of natural and anthropogenic sources of aerosols to assess their importance as a source of Fe to the open ocean. Fe is known to limit primary production in many high nutrient, low chlorophyll areas, so it is important to understand the origin of the Fe that is delivered to the oceans and its availability to marine microorganisms. Additionally, aerosols from different sources have variable size and solubility in seawater and therefore this also impacts Fe bioavailability. Examination of the isotopes of Fe in aerosols could help address these questions as the investigators' prior research has demonstrated distinct variations in the isotopic composition of aerosol Fe that arise from natural and anthropogenic sources. The study will measure the Fe isotopic compositions of aerosol particles collected on Bermuda over a period of one year. Bermuda was chosen as seasonal differences lead to different aerosol types being deposited - summer winds flow from the east and carry Saharan soil dust and other aerosols, while winter winds originate from over North America. The project will compare the Bermuda results with that of key anthropogenic and natural aerosol materials that could be a source of Fe to the Atlantic Ocean. In addition, elemental analyses of these aerosols will provide an independent confirmation of the Fe isotopes results. Analysis of size-segregated samples will provide additional information and will be coupled with solubility experiments designed to assess the soluble Fe fraction. Broader Impacts: The scientific impact of this work relates to obtaining a better understanding of the factors that impact the sources and availability of Fe, an important limiting micronutrient, to the ocean, and to marine microorganisms. As a part of the proposed project, the investigators will develop interactive educational activities to teach the major concepts of ocean nutrient availability and limitation to non-science students, which will be part of a new course "Habitable Worlds". Additionally, the proposed project will support graduate student training, and benefit under-represented groups.