U.S. GEOTRACES Pacific Meridional Transect: Measurements of Actinium-227 to Trace Solute Transport

国际GEOTRACES计划的目标是了解微量化学元素及其同位素在海洋中的分布。该项目将支持测量2018年美国GEOTRACES考察太平洋水样中天然存在的放射性同位素锕-227（Ac-227），该考察从阿拉斯加向南延伸到塔希提岛。此外，研究人员计划分析该项目收集的沉积物岩心中的铅-210和锕-227，以将Ac-227的来源限制在底部沉积物中的水。在水柱中测量Ac-227的价值，特别是如果底部源函数是已知的，在于使用它来测量水的混合和运输速率的潜力。这些运输估计，然后可以应用于了解分布的其他微量元素测量的远征。该项目将支持一名研究生、几名本科生和一名高中生，并与当地退伍军人团体进行外联，鼓励他们参与STEM项目。尽管Ac-227的半衰期（22年）非常适合研究深海中的垂直和横向运输，但在深海中进行的测量很少。仪器的最新进展促进了这种分析，GEOTRACES计划提供的协同作用将为获得更多数据提供理想的机会。此外，AC-227将在确定中太平洋广泛范围内混合率的空间变异性方面具有价值，特别是当与基于Ra-228（6年半衰期）分布的估计相结合时，这是一个合作的GEOTRACES计划将确定的示踪剂场。通过使用具有不同半衰期的多种示踪剂，可以区分混合和平流的影响，从而更全面地了解太平洋深部的动态。这些传输估计，然后可以应用到其他溶质，包括金属和营养物质的浓度场，但将是特别重要的碱度和酸度，这应该有很强的benthic sources.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. This project will support the measurement of the naturally occurring radioisotope actinium-227 (Ac-227) in water samples from the 2018 U.S. GEOTRACES expedition in the Pacific Ocean, running south from Alaska to Tahiti. In addition, the investigators plan to analyze lead-210 and actinium-227 in sediment cores collected by the project, in order to constrain the source of Ac-227 to the water from bottom sediments. The value of measuring Ac-227 in the water column, particularly if the bottom source function is known, lies in the potential to use it to measure rates of mixing and transport of the water. These transport estimates can then be applied to understand the distributions of other trace elements measured on the expedition. The project would support a graduate student, several undergraduates, and a high school student, as well as outreach to local veterans groups encouraging their participation in STEM programs.Despite having a half-life (22 years) that is well suited for the study of both vertical and lateral transport in the deep ocean, few Ac-227 measurements have been made in the deep sea. Recent advances in instrumentation facilitate this analysis, and the synergy provided by the GEOTRACES program will provide an ideal opportunity to obtain additional data. In addition, Ac-227 will be of value in defining the spatial variability of mixing rates across a broad reach of the central Pacific, particularly when combined with estimates based on Ra-228 (6 year half-life) distribution, a tracer field that a collaborating GEOTRACES program will determine. By using multiple tracers with different half-lives, influences of mixing and advection may be distinguished, allowing a more complete understanding of the deep Pacific dynamics. These transport estimates can then be applied to concentration fields of other solutes, including metals and nutrients, but will be of particular importance for alkalinity and silicic acid, which should have strong benthic sources.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.