Collaborative Research: US GEOTRACES PMT: Quantification of Atmospheric Deposition and Trace Element Fractional Solubility

国际GEOTRACES项目的目标是了解海洋中微量化学元素及其同位素的分布。这项工作的一个重要部分是确定海洋微量元素的来源，其中之一来自大气：从空气中落下的灰尘和雨水都将元素输送到海面。该项目将于2018年秋季沿着美国GEOTRACES探险队从阿拉斯加到塔希提岛收集和分析大气中的雨水和颗粒样本。考察的时间与阿拉斯加湾一年中大气尘埃浓度最高的部分相对应，也可能赶上亚洲火灾高峰季节的尾声。相比之下，我们知道，拟议中的航迹南端的大气尘埃含量非常低。在亚洲，气溶胶也会受到人类活动的影响。预计沿航迹大气沉积的差异将有助于评估这一过程对微量元素和同位素循环的作用。该项目将资助一名博士后。海洋大气研究与公众的相关性将与GEOTRACES管理团队合作，在校园开放日活动和在线论坛上进行交流。与GEOTRACES的任务一致，拟议的研究将解决以下生物地球化学和海洋学问题：1)大气气溶胶沉积（干湿）到太平洋表面的大小是多少？2)这些气溶胶的化学成分是什么？其成分如何根据来源（如阿拉斯加冰川粉、亚洲矿物粉尘、生物质燃烧排放、人为排放）而变化？3)太平洋气溶胶中微量元素的溶解度是多少？溶解度是否因气溶胶来源而异？4)可溶性气溶胶铁的潜在生物利用度是多少？5)气溶胶微量元素的可溶部分如何在操作定义的尺寸类别中分布？6)大气沉降如何影响其他GEOTRACES参数的分布？大气气溶胶和降水样本将在70天的考察中收集，调查人员将向合作者和其他感兴趣的科学家提供子样本。这些样品将分析一套关键的微量元素，从散装和大小分馏气溶胶样品，气溶胶渗滤液和雨水样品。由于了解气溶胶微量元素的分数溶解度对未来评估气溶胶衍生微量元素的生物利用度至关重要，因此将在选定的样品上使用顺序萃取方案来根据其FeOx形态和粒度来溶解气溶胶Fe。拟议的工作将为GEOTRACES与大气沉积相关的目标提供直接的数据，并将有助于解决时间变化问题，因为该巡航部分遵循CLIVAR/Repeat Hydrography P16N线。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。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. An essential part of this effort is determining the sources of trace elements to the oceans, one of which is from the atmosphere: dust falling from the air, and rain, both deliver elements to the sea surface. This project would collect and analyze samples of rainwater and of particles from the atmosphere, along a U.S. GEOTRACES expedition from Alaska to Tahiti in the fall of 2018. The timing of the expedition corresponds to the part of the year with the highest atmospheric dust concentrations in the Gulf of Alaska and may also capture the tail end of peak fire season in Asia. In contrast, the southern end of the proposed ship track is known to have very low atmospheric dust. Aerosols will be influenced by human activity in Asia as well. The anticipated differences in atmospheric deposition along the ship track will allow the assessment of the role of this process on trace element and isotope cycling. The project will support a postdoctoral investigator. The relevance of ocean-atmosphere studies to the public will be communicated at campus open house events and in online forums in collaboration with the GEOTRACES management team.In alignment with the mission of GEOTRACES, the proposed research will address the following biogeochemical and oceanographic questions: 1) What is the magnitude of atmospheric aerosol deposition (wet and dry) to the surface of the Pacific Ocean? 2) What is the chemical composition of these aerosols and how does composition vary based on source (e.g. Alaskan glacial flour, Asian mineral dust, emissions from biomass burning, anthropogenic emissions)? 3) What is the fractional solubility of trace elements in Pacific aerosols and does solubility vary based on aerosol source? 4) What is the potential bioavailability of soluble aerosol Fe? 5) How is the soluble fraction of aerosol trace elements distributed across operationally defined size classes? 6) How does atmospheric deposition impact distributions of other GEOTRACES parameters? Atmospheric aerosol and precipitation samples will be collected over the 70-day expedition and the investigators will provide sub-samples to collaborators and other interested scientists. These samples will be analyzed for a suite of key trace elements from bulk and size-fractionated aerosol samples, aerosol leachates, and rain samples. A sequential extraction scheme designed to solubilize aerosol Fe as a function of its FeOx morphology and particle size will be used on selected samples because an understanding of aerosol trace element fractional solubility is fundamental to future work to assess the bioavailability of aerosol derived trace elements. The proposed work will provide data that directly contribute to the GEOTRACES objectives related to atmospheric deposition and will help to address temporal variability as this cruise section follows the CLIVAR/Repeat Hydrography P16N line.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.