NSF GEO-NERC: Constraining the oxic marine sink of novel metal isotope proxies to underpin paleoceanographic reconstructions

NSF GEO-NERC：限制新型金属同位素代理的含氧海洋汇以支持古海洋学重建

• 批准号: 1948716
• 负责人: Sune Nielsen
• 金额: $ 56.1万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-01 至 2025-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948716&HistoricalAwards=false
• 关键词: NSF; GEO; NERC; Constraining; oxic

The evolution of life on Earth is closely tied to conditions, including oxygen levels, in the oceans. Understanding when the oceans first became oxygenated, and how oxygen levels have varied through time, is important to understanding the history of our planet. Chemical clues in marine sediments can be useful in deciphering past conditions. Tools that are currently being investigated as indicators of past oxygen levels include changes in the isotope content of certain trace elements, including thallium, molybdenum, uranium, and zinc. Before these tools can reliably be applied to past sediments, it is important that we understand how these elements are cycled in the present-day ocean, and how they are incorporated into sediments. While most work to date has looked at how these elements and isotopes are incorporated into oxygen-poor sediments, this study would measure these isotopes in a collection of oxygen-rich sediments that spans the world’s oceans. This study would provide essential bounds on marine isotope cycles to better understand modern ocean chemistry and, ultimately, how life and ocean geochemistry co-evolved over Earth history. This study would contribute to the professional development and training of three early-career scientists, and foster international collaboration. This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.This project seeks to understand the modern day cycling of thallium (Tl), molybdenum (Mo), uranium (U) and zinc (Zn) isotopes in the ocean and improve interpretations of paleoceanographic proxies by constraining the oxic deep-sea sediment sink. This goal will be achieved by analyzing the Tl, Mo, U and Zn isotope compositions of the hydrogenous component in a newly assembled set of 73 marine sediment core top samples collected across every ocean basin. The authigenic component of the sediments will be isolated using partial dissolution techniques aimed at only dissolving authigenic minerals. The robustness of these methods will be thoroughly tested using bulk sediment mineral assemblages (obtained by XRD) as well as major and trace element compositions of bulk and partially dissolved samples. The generated dataset will enable an evaluation of the marine oxic output flux magnitude (constrained with 230Th) and stable isotope fractionation for Tl, Mo, U and Zn. A pilot study suggests that the isotope fractionation of these elements is different between Fe-oxides and Mn-oxides within the sediment, which are also unique from ferromanganese crusts and nodules. By expanding the pilot study to a global scale, we will be able to evaluate how previously published records of Tl, Mo, U and Zn isotopes in seawater may need to be reinterpreted due to diverse isotope fractionation patterns in the oxic marine sink.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.

地球上生命的进化与海洋中的条件（包括氧气水平）密切相关，了解海洋何时首次被氧化以及氧气水平如何随时间变化，对于了解我们星球的化学线索非常重要。海洋沉积物可用于破译过去的状况，目前正在研究的工具包括某些微量元素的同位素含量变化，其中包括铊、钼、铀和锌。工具可以可靠地应用于过去的沉积物，但重要的是我们了解这些元素如何在当今的海洋中循环，以及它们如何融入沉积物中，尽管迄今为止的大多数工作都着眼于这些元素和同位素是如何结合的。这项研究将测量遍布世界海洋的富氧沉积物中的这些同位素。这项研究将为海洋同位素循环提供必要的界限，以更好地了解现代海洋化学。这项研究将有助于三名早期职业科学家的专业发展和培训，并促进国际合作。这是一个由美国国家科学基金会地球科学局共同资助的项目。 (NSF/GEO) 和英国国家环境研究委员会 (NERC) 通过 NSF/GEO-NERC 牵头机构协议本协议允许提交一份美国/英国联合提案并进行同行评审。其研究人员拥有最大预算比例的机构在成功联合确定资助后，每个机构都会资助与其本国相关的预算和研究人员的比例。该项目旨在了解铊（Tl）的现代循环。 ）、钼（Mo）、铀（U）和锌（Zn）同位素，并通过限制含氧深海沉积物汇来改善对古海洋代理的解释。这一目标将通过以下方式实现。分析在每个海洋盆地收集的 73 个海洋沉积物岩心顶部样本中的氢成分的 Tl、Mo、U 和 Zn 同位素组成，将使用旨在仅溶解的部分溶解技术来分离沉积物的自生成分。自生矿物。这些方法的稳健性将使用大量沉积物矿物组合（通过 XRD 获得）以及大量和部分溶解样品的主要和微量元素组成进行彻底测试。将能够评估海洋含氧输出通量大小（受限于 230Th）和 Tl、Mo、U 和 Zn 的稳定同位素分馏。一项初步研究表明，这些元素的同位素分馏在铁氧化物和锰氧化物之间是不同的。沉积物中的铁锰结壳和结核也是独一无二的。通过将试点研究扩大到全球范围，我们将能够评估先前发表的 Tl、Mo、由于含氧海洋汇中不同的同位素分馏模式，海水中的 U 和 Zn 同位素可能需要重新解释。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。