Collaborative Research: The benthic influence on North Atlantic deep water eNd signatures

合作研究：底栖生物对北大西洋深水 eNd 特征的影响

• 批准号: 2148005
• 负责人: Brian Haley
• 金额: $ 93.48万
• 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: 2022
• 资助国家: 美国
• 起止时间: 2022-07-15 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2148005&HistoricalAwards=false
• 关键词: Collaborative; Research; benthic; influence; North

The speeds and patterns of deep water currents, collectively known as thermohaline circulation, impact the global distribution of heat and chemicals including dissolved oxygen and carbon dioxide. Modern thermohaline circulation has been described as a "conveyor belt," wherein deep water is formed in the North Atlantic and near Antarctica, then moves throughout the rest of the global oceans. Changes in the location and strength of deep water formation have dramatic impact on both the ocean and on Earth’s climate. However, direct measurement of circulation from Earth’s past is not possible and measuring modern ocean circulation is difficult, because of the inaccessibility of the deep ocean and the vast spatial scales involved, geoscientists must rely on geochemical tracers to understand deep circulation. These tracers allow geoscientists to understand changes in ocean circulation from both modern ocean water and ancient waters recorded in ocean sediments, and thus inform models that predict future change. Observations that the isotopic ratio of the dissolved trace metal neodymium (143Nd and 144Nd) appears to mimic modern deep ocean circulation has meant that this ratio is considered one such circulation tracer. Unfortunately, it is not yet understood why this ratio ostensibly mirrors deep ocean circulation, nor is the established view on the marine geochemical cycle of neodymium completely consistent with observations. To resolve these inconsistencies, the researchers hypothesize that the sediments at the seafloor are a major source of neodymium to the ocean; a proposal in contrast to existing element budgets which consider the sediments to be primarily a sink removing neodymium from the ocean. To test this idea, the investigators will sample sediments, the pore water they contain, and the overlying ocean water from several sites in the North Atlantic, measuring a suite of elements and isotopes in all these samples. This research will contribute to better understand the geochemistry of neodymium and its isotopes in the North Atlantic, one of the regions critical to understanding ocean circulation. Constraining the major controls on neodymium in the ocean is significant to the understanding of ocean-climate interactions as different mechanisms can lead to very different interpretations of the neodymium record of past and present deep water circulation. This improved understanding will result in more accurate interpretations of new and existing data with respect to changes in deep ocean circulation through time and its impact on climate. Neodymium (Nd) is one of 14 rare earth elements (REEs) frequently used to investigate environmental processes. In addition to its use as part of the REE series, the isotope ratio of neodymium (143Nd/144Nd; eNd) is arguably the most promising tracer of past ocean circulation, and is also heavily invested in the GEOTRACES project for the modern ocean. Unfortunately, many observational and theoretical studies indicate that the mechanistic understanding of both of these tracers has considerable problems, leading to potentially erroneous interpretations. The research team prior efforts have concluded that a benthic source of REEs to the oceans exerts a primary control over the distribution of REEs and eNd in deep waters. To date this work has been conducted in the Pacific Ocean, but in this project the investigators will test the hypothesis in the North Atlantic, a region critical for thermohaline circulation. This project will explore fundamental aspects of the geochemical cycle of marine REEs and Nd isotopes. Thus, this work has transformative implications on the understanding and application of the REEs and Nd isotope data in both the modern and ancient oceans. The investigators make the specific and (perhaps) counterintuitive prediction that benthic fluxes of the REEs will be greater in the North Atlantic than those measured in the Pacific. If proven correct, these results will transform the interpretations of a large suite of existing data and provide a more accurate mechanistic understanding of what information these elements provide about modern and past ocean circulation. Even if proven incorrect, the proposed measurements will provide an important contrast to those made in the Pacific and will offer insight into the global geochemical cycling of these elements and their isotopes. Beyond the use and interpretation of neodymium, the work will further the understanding of the importance of the benthic environment on marine trace metal cycling in a general sense (e.g., for iron, copper, zinc, chromium, etc.)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.

被统称为温盐环流的深海水流的速度和模式影响着热量和化学物质（包括溶解氧和二氧化碳）的全球分布。现代温盐环流被描述为“传送带”，其中深层水在北大西洋和南极洲附近形成，然后在全球海洋的其余部分移动。深水形成的位置和强度的变化对海洋和地球气候都有巨大的影响。然而，直接测量地球过去的环流是不可能的，测量现代海洋环流也很困难，因为深海难以进入，涉及的空间尺度很大，地球科学家必须依靠地球化学示踪剂来了解深海环流。这些示踪剂使地球科学家能够从海洋沉积物中记录的现代海水和古代沃茨中了解海洋环流的变化，从而为预测未来变化的模型提供信息。观察到溶解的微量金属钕（143 Nd和144 Nd）的同位素比率似乎模拟了现代深海环流，这意味着这个比率被认为是一种这样的环流示踪剂。不幸的是，目前还不清楚为什么这个比率表面上反映了深海环流，也不是关于钕的海洋地球化学循环的既定观点完全与观测一致。为了解决这些不一致的问题，研究人员假设海底沉积物是海洋钕的主要来源;这一提议与现有的元素预算相反，现有的元素预算认为沉积物主要是从海洋中去除钕的汇。为了验证这一想法，研究人员将从北大西洋的几个地点对沉积物、它们所含的孔隙水以及上覆的海水进行采样，测量所有这些样本中的一系列元素和同位素。这项研究将有助于更好地了解钕及其同位素在北大西洋的地球化学，这是了解海洋环流的关键区域之一。限制钕在海洋中的主要控制是重要的海洋气候相互作用的理解，不同的机制可能会导致非常不同的解释过去和现在的深水循环的钕记录。 这一更好的了解将导致更准确地解释关于深海环流随时间变化及其对气候影响的新数据和现有数据。 钕（Nd）是14种稀土元素之一，常用于研究环境过程。除了作为稀土元素系列的一部分，钕的同位素比值（143 Nd/144 Nd; eNd）可以说是过去海洋环流最有前途的示踪剂，也是现代海洋GEOTRACES项目的重中之重。不幸的是，许多观测和理论研究表明，这两种示踪剂的机械理解有相当大的问题，导致潜在的错误解释。研究小组先前的努力得出结论，海洋中稀土元素的海底来源对深层沃茨中稀土元素和钕的分布具有主要控制作用。迄今为止，这项工作是在太平洋进行的，但在本项目中，调查人员将在北大西洋检验这一假设，这是一个对温盐环流至关重要的区域。该项目将探索海洋稀土元素和钕同位素地球化学循环的基本方面。因此，这项工作具有变革性的影响，在现代和古代海洋的稀土和钕同位素数据的理解和应用。研究人员作出了具体的和（也许）违反直觉的预测，即北大西洋的稀土元素的底栖通量将大于在太平洋测量的通量。如果被证明是正确的，这些结果将改变对大量现有数据的解释，并提供更准确的机械理解，这些元素提供了关于现代和过去海洋环流的信息。即使被证明是不正确的，拟议的测量将提供一个重要的对比，在太平洋地区所做的，并将提供深入了解这些元素及其同位素的全球地球化学循环。除了钕的使用和解释之外，这项工作还将进一步理解海底环境对海洋微量金属循环的重要性（例如，铁、铜、锌、铬等）该奖项反映了NSF的法定使命，并被认为是值得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的支持。