Collaborative Proposal: The benthic influence on north Atlantic deep water eNd signatures

合作提案：底栖生物对北大西洋深水 eNd 特征的影响

• 批准号: 2148481
• 负责人: April Abbott
• 金额: $ 34.94万
• 依托单位: Coastal Carolina 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=2148481&HistoricalAwards=false
• 关键词: Collaborative; Proposal; 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.

深水流（统称为温盐环流）的速度和模式影响热量和化学物质（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”，其中深水在北大西洋和南极洲附近形成，然后流经全球其他海洋。深水形成的位置和强度的变化对海洋和地球气候产生巨大影响。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，因为深海的交通不便且涉及广阔的空间尺度，地球科学家必须依靠地球化学示踪剂来了解深层环流。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水域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。观察到溶解的痕量金属钕（143Nd 和 144Nd）的同位素比率似乎模仿现代深海环流，这意味着该比率被认为是一种这样的环流示踪剂。不幸的是，目前尚不清楚为什么这个比率表面上反映了深海环流，而且关于钕海洋地球化学循环的既定观点也与观测结果并不完全一致。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中钕的主要来源。该提案与现有要素预算形成鲜明对比，现有要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，研究人员将对北大西洋多个地点的沉积物、其中所含的孔隙水以及上覆海水进行采样，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北大西洋的钕及其同位素的地球化学，北大西洋是了解海洋环流的关键区域之一。限制海洋中对钕的主要控制对于理解海洋-气候相互作用具有重要意义，因为不同的机制可能导致对过去和现在深水环流的钕记录的截然不同的解释。 这种加深的理解将导致对新的和现有的数据进行更准确的解释，这些数据涉及深海环流随时间的变化及其对气候的影响。 钕 (Nd) 是经常用于研究环境过程的 14 种稀土元素 (REE) 之一。除了作为 REE 系列的一部分使用之外，钕同位素比（143Nd/144Nd；eNd）可以说是过去海洋环流最有前途的示踪剂，并且还大量投资于现代海洋的 GEOTRACES 项目。不幸的是，许多观察和理论研究表明，对这两种示踪剂的机制理解存在相当大的问题，导致潜在的错误解释。研究小组之前的工作得出的结论是，海洋中稀土元素的底栖来源对深水中稀土元素和 eNd 的分布具有主要控制作用。迄今为止，这项工作已在太平洋进行，但在该项目中，研究人员将在北大西洋（一个对温盐环流至关重要的地区）检验这一假设。该项目将探索海洋稀土元素和 Nd 同位素地球化学循环的基本方面。因此，这项工作对于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变革性的意义。研究人员做出了具体且（可能）违反直觉的预测，即北大西洋的稀土元素海底通量将大于太平洋的稀土元素通量。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，并为这些元素提供的有关现代和过去海洋环流的信息提供更准确的机械理解。即使被证明是错误的，拟议的测量也将与太平洋地区的测量形成重要对比，并将提供对这些元素及其同位素的全球地球化学循环的深入了解。除了钕的使用和解释之外，这项工作还将进一步了解海底环境对一般意义上的海洋微量金属循环（例如铁、铜、锌、铬等）的重要性。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。