US GEOTRACES GP17-OCE: Investigating the role of the Southern Ocean's biogeochemical divide in shaping the global distributions of radium and barium isotopes

GEOTRACES项目旨在了解海洋中微量元素及其同位素的分布。微量元素，就其本质而言，是稀缺的。尽管稀缺，但微量元素是研究海洋过程的宝贵工具，例如：跟踪从陆地或海底向海洋输入的化学物质，识别海洋混合模式，以及追踪海洋生物学。这个项目将通过测量和模拟两种化学上相似的元素——镭和钡的分布来研究这些过程。这些测量将在作为美国GEOTRACES GP17-OCE考察的一部分收集的样本上进行。这支探险队将于2022年底从南大洋采集样本。南大洋经历了深层混合，这对将营养物质带到海面很重要。测量这些样品中的镭和钡同位素将有助于研究支持南大洋及更远海域海洋生物的营养物的来源、循环和汇。这些发现将通过与当地海洋资助计划的合作与地区科学教师和学生分享，这些数据将支持参与GEOTRACES的其他科学家的研究。在过去的25年里，我们对海洋营养循环控制的理解发生了范式转变。现在认为，许多要素的大尺度分布不是由局部垂直过程引起的，而是由发生在南大洋的过程引起的，然后通过侧向环流传播到低纬度地区。循环驱动的机制也被假设有助于镭和钡同位素的全球分布，但这仍有待检验。在这个项目中，伍兹霍尔海洋研究所的研究人员将通过分析从南大洋太平洋地区收集的溶解和颗粒样品中的镭和钡同位素来验证这一假设。这些测量将确定南源模态/中间和底水的组成，它们是全球翻转环流的重要末端成员。该小组还将研究控制端元组成的过程——颗粒的形成和溶解、与沉积物的相互作用、热液作用——并利用统计和力学模型评估它们的重要性。研究结果将揭示南大洋在控制全球镭和钡同位素分布中的作用，这将有助于完善这些示踪剂的应用，作为研究现在和过去海洋生物地球化学过程的工具。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 GEOTRACES program aims to understand the distribution of trace elements and their isotopes in the oceans. Trace elements, by their very nature, are scarce. Despite their scarcity, trace elements are valuable tools for studying marine processes, such as: tracking chemical inputs to the ocean from the land or seafloor, identifying patterns of ocean mixing, and tracing ocean biology. This project will study these processes by measuring and modeling the distributions of two chemically similar elements — radium and barium. These measurements will be made on samples collected as part of the U.S. GEOTRACES GP17-OCE expedition. This expedition will collect samples from the Southern Ocean in late 2022. The Southern Ocean experiences deep mixing, which is important for bringing nutrients to the sea surface. Measuring radium and barium isotopes in these samples will help study the sources, cycling, and sinks of nutrients that support marine biology in the Southern Ocean and beyond. The findings will be shared with regional science teachers and students through a collaboration with the local Sea Grant Program, and the data will support the research of other scientists involved in GEOTRACES.The last 25 years have seen a paradigm shift in our understanding of the controls on marine nutrient cycles. Rather than arising from local vertical processes, the large-scale distributions of many elements are now thought to arise from processes occurring in the Southern Ocean, which are then communicated to lower latitudes through lateral circulation. A circulation-driven mechanism is also hypothesized to contribute to the global distributions of radium and barium isotopes, but this remains to be tested. In this project, researchers from the Woods Hole Oceanographic Institution will test this hypothesis by analyzing radium and barium isotopes in dissolved and particulate samples collected from the Pacific Sector of the Southern Ocean. These measurements will establish compositions for the southern-sourced mode/intermediate and bottom waters that are important end-members in the global overturning circulation. The team will also study the processes that control the composition of the end-members — particle formation and dissolution, interactions with sediments, hydrothermalism — and assess their significance using statistical and mechanistic modeling. The results will reveal the role of the Southern Ocean in controlling the global distributions of radium and barium isotopes, which will help refine the application of these tracers as tools for studying biogeochemical processes in the present and past 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.