Are iron nanoparticles in wet deposition a potential source of bioavailable Fe to marine algae?

矿物尘为海洋生态系统提供铁、磷等营养物质，是大气CO2的主要汇。这些营养素已被证明可以促进浮游植物等固定二氧化碳的海洋微生物的生长，从而间接影响气候系统。对这种影响的定量理解对于模拟地球气候系统并因此预测气候变化至关重要。然而，这种影响目前没有得到充分的模拟，因为来自大气沉积物（干和湿）的生物可利用铁通量是连接地球系统模型的两个主要组成部分的关键参数（即，HadGEM 2）中的气溶胶和生态系统成分的定量化较差。生物可利用铁的海洋通量取决于（1）总粉尘沉降通量，（2）总铁含量的灰尘和（3）铁的生物可利用性的灰尘。在这三个参数中，铁的生物利用度是最不确定的。作为一个重要的，有时是主要的来源，铁的海洋，我们选择集中在湿沉降在这项工作中。目前，模型通常假设所有测量的溶解铁在湿沉降是生物可利用的。然而，在雨水的“溶解”部分中，大部分铁是以纳米颗粒的形式存在的，这在我们最近的一项研究中已经被确定（并可视化）。因此，为了改善全球海洋生物可利用铁通量的模型估计，量化雨水中铁纳米颗粒的生物可利用性是必要的。这项工作的目标是确定如何生物可利用的铁纳米粒子在自然雨水的模式生物海链藻，一个典型的海洋浮游植物（中心硅藻）。这将有助于更准确地估计地球系统模型的生物有效铁通量的全球海洋。该项目的具体目标是：1）证明实验室合成的具有有机涂层的Fe纳米颗粒可以为海链藻提供生物可利用的Fe 2）量化实验室处理的矿物粉尘中Fe纳米颗粒的生物可利用性（经模拟酸处理后，再进行云雾处理）对海链藻的影响3）为了量化天然雨水中Fe纳米颗粒对海链藻的生物利用度，这些目标旨在回答三个复杂程度的问题。实现每个目标的实验将为解释更复杂和更具环境代表性的后续实验提供数据。这些目标将通过实验室纳米颗粒合成、纳米颗粒分离和表征以及实验室海藻培养来实现。将使用NERC环境纳米科学分析和表征设施（FENAC）提供的最先进技术，如扫描透射电子显微镜、纳米颗粒跟踪分析、流场流分级和交叉流超滤，进行纳米颗粒分离和表征。伯明翰大学的地球化学和微生物学实验室将用于纳米粒子合成和海藻培养。研究人员在大气化学和全球地球化学循环方面的专业知识得到了微生物学方面的命名研究员Michala Pettitt博士的补充。我们的专业知识得到了伯明翰大学纳米科学和环境科学教授Jamie Lead和Roy Harrison的进一步加强。科学成果将发表在国际同行评审期刊上，并提供给全球模型，如英国化学和气溶胶模型（UKCA），以改善对大气生物有效铁沉积通量的估计，该模型可以随时提供给英国气象局地球系统模型（HadGEM 3），以预测大气营养物质输入对海洋生产力和气候的影响。

SummaryMineral dust provides nutrients such as iron and phosphorus to marine ecosystem, which is a major sink for atmospheric carbon dioxide. These nutrients have been shown to promote the growth of CO2-fixing marine microorganisms such as phytoplankton, and therefore indirectly affect the climate system. A quantitative understanding of this effect is essential to model the Earth's climatic systems and therefore to predict climate change. However, this effect is currently inadequately modeled because the bioavailable iron flux from atmospheric depositions (both dry and wet), a key parameter to link two major components of earth system models (i.e., AEROSOLS and ECOSYSTEMS components in HadGEM2), is poorly quantified. The bioavailable iron flux to the ocean is dependent on (1) the total dust deposition flux, (2) total iron content in the dust and (3) bioavailability of iron in the dust. In these three parameters, iron bioavailability is the most uncertain one. As a significant and sometimes predominant source of iron to the ocean, we choose to focus on wet deposition in this work. Currently, models often assumed that all the measured dissolved Fe in the wet deposition is bioavailable. However, a large proportion of Fe in the 'dissolved' fraction of rainwater is present as nanoparticles, which have been identified (and visualized) in one of our recent studies. Therefore, to improve the model estimates of the bioavailable iron flux to the global ocean, it is essential to quantify the bioavailability of iron nanoparticles in the rainwater. The goal of this work is to determine how bioavailable are the Fe nanoparticles in natural rainwater to a model organism Thalassiosira pseudonana, a typical marine phytoplankton (centric diatom). This will contribute to a more accurate estimate of the bioavailable iron flux to the global ocean for earth system models. The specific objectives of this project are: 1) To demonstrate that laboratory synthesized Fe nanoparticles with organic coatings can provide bioavailable Fe to Thalassiosira pseudonana 2) To quantify the bioavailability Fe nanoparticles in laboratory-processed mineral dust (after simulated acid and then cloud processing) to Thalassiosira pseudonana 3) To quantify the bioavailability of Fe nanoparticles in natural rainwater to Thalassiosira pseudonanaThese objectives are designed to answer questions of three levels of complexity. The experiment to realize each objective will provide data to interpret the more complex and more environmentally representative later experiments. These objectives will be met by laboratory nanoparticle synthesis, nanoparticle separation and characterization as well as laboratory marine algal culturing. State-of-the-art techniques such as Scanning Transmission Electron Microscopy, nanoparticle tracking analysis, Flow Field Flow Fractionation and Cross Flow Ultrafiltration available at the NERC Facility for Environmental Nanoscience Analysis and Characterisation (FENAC) will be used for nanoparticle separation and characterization. The geochemical and microbiology laboratories in the University of Birmingham will be used for nanoparticle synthesis and marine algal culture. The expertise of the investigator in atmospheric chemistry and global biogeochemical cycles is complemented by that of Named Researcher, Dr. Michala Pettitt, in microbiology. Our expertise is further enhanced by those of Prof. Jamie Lead and Prof. Roy Harrison in nanoscience and environmental sciences at the University of Birmingham. The scientific results will be published in international peer-reviewed journals and fed to global models such as UK Chemistry and Aerosol Model (UKCA) to improve the estimation of atmospheric bioavailable iron deposition flux, which can be readily fed to and Met Office Earth system model (HadGEM3) to predict the impact of atmospheric nutrient input on ocean productivity and climate in the present and the future.