OCE-PRF Isotopic and microbial investigations of the iron geochemistry and bioavailability of glaciogenic particles

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。微量元素如铁在海洋生物过程中起着重要作用。在浮游植物生长并支持海洋食物网基础的地表水中，铁通常以极低的浓度存在，靠近两极，可以限制浮游植物的生产力。由于海洋普遍缺铁，微生物已经发展出专门的策略来获取即使是相对难以获得的矿物形式的铁，如颗粒物质。富铁颗粒的一个来源是冰川融水流入海洋，随着气候持续变暖，预计融水将增加。这里提出的研究旨在研究冰川融化提供的铁与微生物利用这种新铁营养来源的能力之间的关系。为了做到这一点，微生物的生长将在两个受冰川严重影响的沿海地区的冰川冰颗粒上进行测试：南极洲和阿拉斯加。该项目将支持培养一名博士后学者，并支持PI参与阿拉斯加本土科学与工程项目（ANSEP）和斯克里普斯本科生研究奖学金（SURF）项目开展的教育和推广活动，包括指导一名本科生进行研究项目。冰川融水由于其高含量的生物可利用铁（Fe），预计将成为高纬度海洋的肥料。冰川来源的铁的生物利用度通常是从大小和化学不稳定性来推断的，以前的生物系统研究使用有限数量的铁基质来探测选定浮游植物物种的生物利用度。对海洋环境中冰川期铁获取和生物吸收的机制理解仍然是需要的。充分表征冰川期铁的地球化学和微生物获取的机制研究有可能极大地帮助我们了解冰川融水供应与生态系统生产力之间的耦合相互作用。本研究旨在评估冰川衍生含铁颗粒的生物利用度，方法是结合对离散冰川冰块中经化学处理的冰川形成颗粒的铁同位素组成的检测，以及利用转基因海洋异养细菌进行的生长实验。关于冰川期颗粒的化学不稳定性和生物可利用性，本文提出了两种假设：1)冰川期颗粒的铁稳定同位素特征与化学不稳定性有关，可以用来衡量沉积物输送到海洋环境的施肥潜力及其随后的命运；2)化学稳定性可以通过微生物获取铁直接与生物利用度联系起来，而生物利用度反过来又影响铁稳定同位素特征。该项目有助于我们了解哪些海洋微生物群落成员将受益于冰川衍生的铁，铁获取策略在铁同位素特征和海洋系统生物可利用性中的作用，以及冰冻圈风化输入增加对海洋的施肥潜力。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).Trace element micronutrients such as iron, play important roles in biological processes in the ocean. In surface waters where phytoplankton grow and support the base of the marine food web, iron is often present at vanishingly small concentrations and near the poles, can limit phytoplankton productivity. Motivated by widespread oceanic iron deficiency, microbes have developed specialized strategies for accessing even relatively unavailable mineral forms of iron, such as particulate matter. One source of iron-rich particles is the delivery of glacial meltwater to the ocean, which is expected to increase as the climate continues to warm. The research proposed here seeks to study the relationships between iron supplied from the melting of glaciers and the ability of microbes to take advantage of this new source of iron nutrition. To do this, the growth of microbes will be tested on glacial ice particles from two coastal locations heavily influenced by glaciers: Antarctica and Alaska. This project will support the training of a postdoctoral scholar, and the participation of the PI in education and outreach activities carried out through the Alaskan Native Science & Engineering Program (ANSEP) and Scripps Undergraduate Research Fellowship (SURF) programs, including mentorship of an undergraduate in a research project. Glacial meltwater is expected to fertilize the high-latitude oceans due to its high content of bioavailable iron (Fe). Bioavailability of glacially-derived Fe is typically inferred from size and chemical lability, and previous investigations in biological systems use a limited number of Fe substrates to probe the bioavailability with select phytoplankton species. A mechanistic understanding of glaciogenic Fe acquisition and biological uptake in marine environments is still needed. Mechanistic studies which fully characterize the geochemical and microbial acquisition of glaciogenic iron have the potential to greatly inform our understanding of the coupled interaction between the supply of glacial meltwater and ecosystems productivity. This proposal seeks to assess the bioavailability of glacially-derived Fe-bearing particles by combining examinations of the Fe isotopic composition of chemically treated glaciogenic particles from discrete glacial ice pieces with growth experiments using a genetically-modified marine heterotrophic bacteria. Two hypotheses regarding chemical lability and bioavailability of glaciogenic particles will be examined in the proposed work: 1) The Fe-stable isotopic signatures of glaciogenic particles are linked to chemical lability, and can be used to gauge the fertilization potential of sediment transported to marine environments and its subsequent fate; and 2) Chemical lability can be directly linked to bioavailability via microbial iron acquisition, which in turn affects Fe-stable isotopic signatures. This project stands to contribute to our understanding of which members of the marine microbial community will benefit from glacially-derived Fe, the role of Fe acquisition strategies in Fe isotopic signatures and bioavailability in marine systems, and the fertilization potential of increased cryospheric weathering inputs to the ocean.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.