Collaborative Research: How and Why eNd Tracks Ocean Circulation

合作研究：eNd 如何以及为何追踪海洋环流

• 批准号: 1850789
• 负责人: Benjamin Twining
• 金额: $ 32.54万
• 依托单位: Bigelow Laboratory for Ocean Sciences
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-05-15 至 2024-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1850789&HistoricalAwards=false
• 关键词: Collaborative; Research; How; Why; eNd

Circulation of water is a fundamental trait of the oceans that impacts its physics, chemistry and biology; however, understanding modern and past patterns of circulation - especially in the vast bodies of deep water - is challenging because global circulation defies direct measurement. The problems with direct measurement largely stem from the vast scales of space and time that are of interest in understanding global circulation. One tool for estimating global circulation patterns that holds promise is seen in neodymium isotopes which appear to be powerful tracers of deep ocean circulation, over a variety of timescales. Unfortunately, the elemental behavior of neodymium contrasts the isotopic behavior of neodymium in the oceans, a puzzle branded the "neodymium paradox." This inconsistency of geochemical behavior opens to question the application of neodymium isotopes as a tracer of circulation. Therefore, scientists from Oregon State University, Tulane University, and Bigelow Laboratory of Ocean Sciences propose to test the hypothesis that there is a yet unconstrained (even poorly identified) source of neodymium to the oceans that can explain the discrepancies seen between the elemental and isotopic neodymium marine budgets. The scientists further seek to understand the mechanistic cause of this source and thus be able to start making global constraints on its influence. Understanding these processes will fundamentally change our interpretations of neodymium data and allow us to more accurately quantify ocean circulation with a greater degree of confidence. For outreach activities, the scientists plan to participate in open house days held at Oregon State University, da Vinci days, National Ocean Science Bowls, Salmon Bowl and Bigelow Laboratory for Ocean Sciences' Cafe Scientifique. Undergraduate students and one graduate student from Tulane University would be supported and trained as part of this project. Scientists from Oregon State University, Tulane University, and Bigelow Laboratory for Ocean Sciences propose to test the hypothesis that there is a benthic source of neodymium (Nd) to the oceans that exerts a primary control over the distribution of this element and its isotopes (eNd) in the ocean. This benthic flux results from early diagenetic reactions that release rare earth elements (REEs) from the solid phase to pore fluid. The scientists contend this flux will explain eNd distributions throughout the modern and past global oceans. The planned research will be guided by three questions:(1) What are the mechanisms that control the magnitude and isotope composition of the benthic flux?(2) What are the relationships among bottom water, pore fluid, and the terminal solid phase compositions? Particularly, how and under what chemical conditions does an eNd signature become part of a preserved archival record of [Nd] and eNd?(3) Can our understanding of the deep water benthic fluxes account for the integrated bottom water eNd as a function of apparent water mass age and circulation path (e.g., how do the pore fluid and solid phase values reconcile with the existing water column signature and water mass age data)?To test these ideas, sediments and their pore fluids will be collected from a diverse set of deep sea sites in the Pacific Ocean that reflect slow-to-fast sedimentation rates, carbonate-, terrigenous-, volcaniclastic- and siliceous-sediment, and low-to-high organic carbon. The sediments and porewater samples, as well as samples from the overlying water column will be characterized for the following parameters: major, minor, and trace metals, Nd isotopes, carbonate chemistry, oxygen, nutrients, particulate organic carbon, particulate organic nitrogen, radiocarbon, porosity, and grain size. With these observations we will build a quantitative numeric geochemical model (e.g., PHREEQC, Geochemist's Workbench, Humic Ion Binding Model) that can capture the cardinal controls over the benthic source. Our goal is to provide a new interpretive framework for Nd and eNd, such that we can offer quantitative estimates of benthic fluxes for use in models of global circulation. This work has potentially transformative implications on our understanding and application of REEs and Nd isotope data in both the 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.

水的循环是影响其物理，化学和生物学的海洋的基本特征。但是，了解现代和过去的循环模式，尤其是在深水的巨大体内，这是具有挑战性的，因为全球循环违反了直接测量。 直接测量的问题在很大程度上源于在理解全球循环的广泛时空和时间范围内。 在各种时间尺度上，在近代的同位素中可以看到一种估计全球循环模式的工具，这些工具似乎是深海循环的强大示踪剂。 不幸的是，新近二岛的元素行为与海洋中新生虫的同位素行为形成了鲜明的对比，这个拼图标记了“北极悖论”。 地球化学行为的这种不一致使质疑新近同位素作为循环的示踪剂的应用。 因此，俄勒冈州立大学，图兰大学和海洋科学实验室的科学家建议检验以下假设：尚未受到约束（甚至很差）向海洋的新近媒体来源，可以解释可以解释元素和同位素新医生预算之间的差异。 科学家们进一步寻求了解该来源的机械原因，从而能够开始对其影响进行全球限制。 了解这些过程将从根本上改变我们对近代数据的解释，并使我们能够更加准确地量化海洋循环。 为了进行外展活动，科学家计划参加俄勒冈州立大学，达芬奇时代，国家海洋科学碗，鲑鱼碗和海洋科学咖啡馆科学实验室的开放日期。 本科生和一名来自杜兰大学的研究生将获得该项目的一部分。 俄勒冈州立大学，杜兰大学和海洋科学实验室的科学家建议检验以下假设：底栖近代的近代矿山（ND）的来源对海洋施加了对该元素及其同位素（其同位素（End））海洋分布的主要控制。 这种底栖通量是由早期的成岩反应引起的，该反应释放了从固相到孔隙流体的稀土元素（REE）。 科学家认为，这种通量将解释整个现代和过去的全球海洋中的最终分布。计划的研究将以三个问题为指导：（1）控制底栖通量的幅度和同位素组成的机制是什么？（2）底水，孔隙流体和末端固相组成之间有什么关系？特别是，终端签名如何成为[nd]和结束的保留档案记录的一部分？（3）我们对深水底栖通量的理解能够解释底部水的终端的一部分？从太平洋中的一组深海地点收集，反映了缓慢的沉积速率，碳酸盐，地缘，火山碎裂和硅质 - 阳离子，以及低到高的有机碳。 沉积物和孔水样品以及上上覆的水柱中的样品的特征是以下参数：主要，小型，小型和微量金属，ND同位素，碳酸盐化学，氧气，氧气，营养素，颗粒有机碳，颗粒有机碳，颗粒有机氮，辐射氮，孔隙率和晶粒尺寸。 通过这些观察，我们将构建一个定量的数字地球化学模型（例如，地球化学家的工作台，腐殖离子结合模型），可以捕获底栖源的基本控制。 我们的目标是为ND和End提供一个新的解释框架，以便我们可以对底栖通量进行定量估计，以用于全球循环模型。 这项工作对我们在现代和古老海洋中对REE和ND同位素数据的理解和应用具有潜在的变革意义。该奖项反映了NSF的法定任务，并使用基金会的智力优点和更广泛的影响评估审查标准，被认为值得通过评估来支持。

项目成果

Potassium isotope signatures in modern marine sediments: Insights into early diagenesis

• DOI: 10.1016/j.epsl.2022.117849
• 发表时间: 2022-12
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Wenshuai Li;Xiao-ming Liu;Kun Wang;J. McManus;B. Haley;Yoshio Takahashi;Mohsen Shakouri;Yongfeng Hu

Reactive-transport modeling of neodymium and its radiogenic isotope in deep-sea sediments: The roles of authigenesis, marine silicate weathering and reverse weathering

• DOI: 10.1016/j.epsl.2022.117792
• 发表时间: 2022-09-08
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Du, Jianghui;Haley, Brian A.;Vance, Derek
• 通讯作者: Vance, Derek