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: 1850765
• 负责人: Brian Haley
• 金额: $ 36.76万
• 依托单位: Oregon State University
• 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=1850765&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.

水循环是海洋的一个基本特征，影响其物理、化学和生物学；然而，了解现代和过去的环流模式（尤其是在广阔的深水中）具有挑战性，因为全球环流无法直接测量。 直接测量的问题很大程度上源于理解全球循环所需要的广阔的空间和时间尺度。 钕同位素是一种有望用于估计全球环流模式的工具，它似乎是各种时间尺度的深海环流的强大示踪剂。 不幸的是，钕的元素行为与海洋中的同位素行为形成鲜明对比，这个谜题被称为“钕悖论”。 这种地球化学行为的不一致引发了对钕同位素作为循环示踪剂的应用的质疑。 因此，来自俄勒冈州立大学、杜兰大学和毕格罗海洋科学实验室的科学家提议检验这样一个假设：海洋中存在一种尚未受到限制（甚至尚未确定）的钕来源，该来源可以解释元素和同位素钕海洋预算之间的差异。 科学家们进一步寻求了解这一来源的机械原因，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钕数据的解释，并使我们能够更加准确、更有信心地量化海洋环流。 对于外展活动，科学家们计划参加在俄勒冈州立大学举办的开放日、达芬奇日、国家海洋科学碗、鲑鱼碗和毕格罗海洋科学实验室的科学咖啡馆。 作为该项目的一部分，杜兰大学的本科生和一名研究生将得到支持和培训。 来自俄勒冈州立大学、杜兰大学和毕格罗海洋科学实验室的科学家提议检验这样一种假设：海洋中存在着海底的钕 (Nd) 来源，该来源对该元素及其同位素 (eNd) 在海洋中的分布发挥着主要控制作用。 这种底栖通量是由早期成岩反应引起的，该反应将稀土元素 (REE) 从固相释放到孔隙流体中。 科学家们认为，这种通量将解释整个现代和过去全球海洋的 eNd 分布。计划的研究将围绕三个问题进行指导：（1）控制底栖通量大小和同位素组成的机制是什么？（2）底水、孔隙流体和终端固相组成之间的关系是什么？特别是，eNd 特征如何以及在什么化学条件下成为 [Nd] 和 eNd 保存的档案记录的一部分？（3）我们对深水底栖通量的理解能否将综合底水 eNd 解释为表观水团年龄和循环路径的函数（例如，孔隙流体和固相值如何与现有水柱特征和水团年龄数据相一致）？为了检验这些想法，沉积物及其孔隙流体将被 从太平洋不同的深海地点收集，这些地点反映了从慢到快的沉积速率、碳酸盐、陆源、火山碎屑和硅质沉积物，以及从低到高的有机碳。 沉积物和孔隙水样品以及来自上覆水柱的样品将表征以下参数：主要、次要和痕量金属、Nd 同位素、碳酸盐化学、氧、营养物、颗粒有机碳、颗粒有机氮、放射性碳、孔隙度和粒度。 通过这些观察，我们将建立一个定量数值地球化学模型（例如，PHREEQC、地球化学家工作台、腐殖离子结合模型），该模型可以捕获对底栖来源的主要控制。 我们的目标是为 Nd 和 eNd 提供一个新的解释框架，以便我们可以提供用于全球环流模型的底栖通量的定量估计。 这项工作对我们对现代和古代海洋中稀土元素和 Nd 同位素数据的理解和应用具有潜在的变革性影响。该奖项反映了 NSF 的法定使命，并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，被认为值得支持。