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.

深水电流的速度和模式，统称为热盐循环，影响热和化学物质的全球分布，包括溶解的氧气和二氧化碳。现代的热盐循环被描述为“传送带”，其中在北大西洋和南极附近形成深水，然后在整个全球海洋中移动。深水形成的位置和强度的变化对海洋和地球的气候都产生了巨大影响。但是，无法直接测量地球过去的循环，并且很难测量现代海洋循环，因为深海和涉及的广泛空间尺度的难以接近，地球科学家必须依靠地球化学示踪剂来了解深层循环。这些示踪剂使地球科学家能够了解来自现代海水和海洋沉积物中的古老水的海洋循环变化，从而为预测未来变化的模型提供了信息。观察到溶解的痕量金属邻居的同位素比（第143和第144位）似乎模仿了现代深海循环，这意味着该比率被认为是这样的循环示踪剂。不幸的是，这尚不理解为什么表面上可以反映海洋循环的原因，也没有对新近媒体的海洋地球化学循环的既定观点完全与观察结果一致。为了解决这些不一致之处，研究人员假设海底的沉积物是海洋的主要来源。与现有元素预算相反的提案，该提案认为沉积物是主要的水槽，从海洋中去除霓虹灯。为了测试这一想法，研究人员将采样沉积物，所含的孔隙水以及来自北大西洋多个地点的上覆的海水，在所有这些样品中测量了一套元素和同位素。这项研究将有助于更好地了解北大西洋的新近山及其同位素的地球化学，这是对了解海洋循环至关重要的地区之一。限制海洋近代的主要控制对于对海洋气候相互作用的理解意义重大，因为不同的机制可能会导致对过去和现在深水循环的新近岛记录的解释。这种改善的理解将导致对新数据和现有数据的更准确的解释，这些数据随着时间的流逝而变化及其对气候的影响。 Neododmium（ND）是经常用于研究环境过程的14种稀土元素（REE）之一。除了用作REE系列的一部分之外，Neododium（143/144nd; End）的同位素比也可以说是过去海洋循环中最有希望的示踪剂，并且在现代海洋的Geotraces项目中也大量投资。不幸的是，许多观察性研究和理论研究表明，对这两种示踪剂的机理理解都考虑了问题，导致了潜在的错误解释。研究团队的事先努力得出的结论是，海洋的底栖底栖来源对REES的分布产生了主要控制，并在深水中结束。迄今为止，这项工作是在太平洋进行的，但是在这个项目中，研究人员将测试北大西洋的假设，北大西洋是热盐循环至关重要的地区。该项目将探讨海洋雷斯和ND同位素的地球化学周期的基本方面。这是对REES和ND同位素数据在现代和古代海洋中的理解和应用的变革含义。研究人员对北大西洋中REE的底栖通量的特定和（也许）的违反直觉预测要比太平洋地区所测量的范围更大。如果被证明是正确的，这些结果将改变一大堆现有数据的解释，并对这些元素提供有关现代和过去海洋循环的信息提供更准确的机械理解。即使被证明是不正确的，提议的测量将与太平洋中的测量值形成重要对比，并将深入了解这些元素及其同位素的全球地球化学循环。除了使用和解释新山岛之外，这项工作还将进一步理解底栖环境对海洋痕量金属循环的重要性（例如，对于铁，铜，锌，铬等），该奖项反映了NSF的法定任务，并认为通过基金会的知识优点和广泛的criperia来评估通过评估来获得评估。