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

国际地学研究计划的目标是了解海洋中痕量化学元素及其同位素的分布。这项工作的一个关键部分是确定海洋中痕量元素的来源，其中一种来自大气：从空气中落下的尘埃和雨水都会将元素输送到海面。该项目将于2018年秋天沿着美国地理跟踪探险队从阿拉斯加到塔希提岛的路线收集和分析雨水和大气中的颗粒物样本。这次探险的时间与阿拉斯加湾大气粉尘浓度最高的部分相对应，也可能捕捉到亚洲火灾旺季的尾声。相比之下，拟议中的航道的南端已知大气粉尘非常低。气溶胶也将受到亚洲人类活动的影响。船舶航道上大气沉积的预期差异将使我们能够评估这一过程对痕量元素和同位素循环的作用。该项目将支持一名博士后研究员。将与GEOTRACES管理团队合作，在校园开放活动和在线论坛上宣传海洋-大气研究与公众的相关性。根据GEOTRACES的使命，拟议的研究将解决以下生物地球化学和海洋学问题：1)太平洋表面大气气溶胶沉积(湿和干)的规模是多少？2)这些气溶胶的化学成分是什么，成分根据来源(例如阿拉斯加冰粉、亚洲矿物粉尘、生物质燃烧排放)有何不同，人为排放)？3)太平洋气溶胶中痕量元素的溶解度百分比是多少？溶解度是否因气溶胶来源不同而不同？4)可溶气溶胶铁的潜在生物有效性是多少？5)气溶胶痕量元素的可溶分数是如何在操作定义的尺寸类别中分布的？6)大气沉积如何影响其他GEOTRACES参数的分布？在为期70天的探险中，将收集大气气溶胶和降水样本，调查人员将向合作者和其他感兴趣的科学家提供子样本。这些样本将从散装和分级气溶胶样本、气溶胶渗滤液和雨水样本中分析一套关键的微量元素。将对选定的样品使用顺序提取方案，该方案旨在根据FeOx的形态和颗粒大小来增溶气溶胶中的铁，因为了解气溶胶中痕量元素的部分溶解度是评估气溶胶中痕量元素的生物利用度的未来工作的基础。拟议的工作将提供直接有助于GEOTRACES与大气沉积相关的目标的数据，并将有助于解决时间变异性，因为这一巡航部分遵循CLIVAR/重复水文P16N线。这一奖励反映了NSF的法定使命，并通过使用基金会的智力优势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.