Collaborative Research: US GEOTRACES GP17-ANT: Constraining the Neodymium (Nd) Isotope and Rare Earth Element Cycles near the Amundsen Sea Continental Margin

海水中的微量元素与气候和人类社会有关，因为它们可以作为海洋生态系统的必要营养物质或各种海洋过程的有用化学指纹。国际GEOTRACES计划旨在确定控制全球海洋中关键微量元素及其同位素分布的过程和通量，并确定这些分布如何对不断变化的环境做出反应。钕(ND)同位素和稀土元素(REE)是这类关键元素的显著例子，因为它们可用于追踪过去和现在的海洋混合以及海洋中的微量元素来源。在这个项目中，调查人员将参加美国GEOTRACES科学考察队GP17-ANT到南极大陆边缘阿蒙森海段的考察，并分析这次考察队采集的样品中的ND同位素比率和稀土元素浓度。这一海洋区域具有特别重要的意义，因为在过去的几十年里，它正在经历快速的环境变化，包括整个南极周围冰架融化的最快速度。该项目的测量结果将促进我们对导致当地冰架融化的海洋过程的理解，并将为维持该地区上层海洋异常高的生物生产力的营养来源提供新的线索。该项目将有助于支持不同职业层次的南极研究、教学和外联工作的发展。外展活动将提供大量的机会，让K-12学生、来自代表性不足的群体的学生和公众在正式和非正式的环境中参与海洋科学和南极环境的讨论。美国GEOTRACES GP17-ANT邮轮前往阿蒙森海提供了一个特殊的机会，研究与南极大陆边缘、快速冰盖融化、生产性多年生生物和水团过程有关的微量元素及其同位素的海洋生物地球化学循环。该项目将研究调节该地区海水中ND同位素和稀土元素分布的来源和过程。将研究并尽可能量化的具体来源和过程包括：(1)水团传输和混合；(2)坡度交换；(3)气溶胶；(4)海冰；(5)冰下融水；(6)沉积物和陆架交换；(7)颗粒相互作用。将对一套精心挑选的海水、颗粒物、沉积物、气溶胶和海冰样品进行Nd同位素和稀土元素浓度分析，以限制这些不同控制措施的性质和相对意义，从而全面了解南极边缘的ND同位素和稀土元素循环。这些结果不仅将对与理解该地区所有其他微量元素生物地球化学循环直接相关的水团过程和成岩输入提供关键限制，而且还将提高ND同位素和REE模式作为研究现代和古代海洋的有用示踪剂的效用。这一奖项反映了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。

Trace elements in seawater are relevant to climate and human society, because they can act as essential nutrients for marine ecosystems or useful chemical fingerprints for a variety of oceanographic processes. The international GEOTRACES program is intended to identify processes and quantify fluxes that control the distributions of key trace elements and their isotopes in the global ocean, and to establish how these distributions could respond to changing environments. Neodymium (Nd) isotopes and rare earth elements (REEs) are notable examples of such key elements because of their utility in tracing past and present ocean mixing and sources of trace elements to the ocean. In this project, investigators will participate in the US GEOTRACES science expedition GP17-ANT to the Amundsen Sea sector of the Antarctic continental margin, and analyze Nd isotope ratios and REE concentrations in samples collected from this expedition. This region of the ocean is of particular significance because it is experiencing rapid environmental changes in the past few decades, including the fastest melting of ice shelves around the entire Antarctic. Measurements from this project will advance our understanding of ocean processes that cause melting of local ice shelves, and also will shed new light on nutrient sources that sustain the unusually high biological productivity in the upper ocean of this region. This project will contribute to support the development of diverse involvement in Antarctic research, teaching and outreach efforts across career levels. The outreach activities will provide ample opportunities to engage K-12 students, students from underrepresented groups, and general public in discussions of ocean sciences and the Antarctic environment in both formal and informal settings.The US GEOTRACES GP17-ANT cruise to the Amundsen Sea provides an exceptional opportunity to study marine biogeochemical cycles of trace elements and their isotopes in relation to the Antarctic continental margin, fast iceshelf melting, productive polynyas, and water mass processes in an area especially susceptible to ongoing climate change. This project will study sources and processes that regulate the distribution of Nd isotopes and REEs in seawater in this region. Specific sources and processes that will be studied, and quantified where possible, include: (1) water mass transport and mixing; (2) slope exchange; (3) aerosols; (4) sea ice; (5) subglacial meltwaters; (6) sediments and shelf exchange; (7) particle interactions. Nd isotope and REE concentration analyses will be conducted on a suite of carefully selected seawater, particulate, sediment, aerosol, and sea ice samples to constrain the nature and relative significance of these different controls, providing a comprehensive understanding of Nd isotope and REE cycling in the Antarctic margin. These results will not only provide critical constraints on water mass processes and lithogenic inputs that are directly relevant to understand all other trace element biogeochemical cycles in this region, but also improve the utility of Nd isotopes and REE patterns as useful tracers for studies of modern and ancient oceans.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.