Collaborative Research: Towards a Better Understanding of Tl Isotope Cycling under Different Redox Conditions

合作研究：更好地理解不同氧化还原条件下的 Tl 同位素循环

• 批准号: 2128939
• 负责人: Elizabeth Swanner
• 金额: $ 5.36万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-12-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128939&HistoricalAwards=false
• 关键词: Collaborative; Research; Towards; Better; Understanding

The element thallium (Tl) is gaining momentum as a tool for reconstructing the history of molecular oxygen (O2) in Earth’s ancient oceans. Reconstructing this history is important because the availability of O2 in Earth’s ancient oceans played a key governing role in the origin and evolution of life on our planet. Furthermore, ongoing deoxygenation of modern oceans will affect every human on Earth, and we can better predict and prepare for this deoxygenation if we understand comparable events in Earth’s past. The utility of Tl to track changes in marine O2 stems from the fact that its isotopes are strongly fractionated by interactions with manganese (Mn) oxide minerals, which are formed and buried in marine sediments today only where O2 is present. Indeed, many studies show that Tl isotope ratios preserved in ancient marine rocks can provide important information about past O2 availability in the ocean. Yet, our understanding of the modern Tl isotope cycle is far from complete, due largely to the extremely low abundances of Tl found in environments today, which make it difficult to collect enough material for accurate Tl isotopic analysis. The PIs’ preliminary work in a brackish pond on Cape Cod (Siders Pond) show that it is feasible to generate quality Tl isotope data for water, particles, and sediments in an environment with very low Tl abundances. Furthermore, early results from this work provide important new information about the links that connect Tl isotopes to Mn oxides, and Mn oxides to O2 – links that were probably also present in ancient marine environments. It is the PIs’ plan to upscale their work in Siders Pond and extend it to two freshwater lakes in Minnesota (Deming and Steel lakes). The results of this work will vastly improve our understanding of the modern Tl isotope cycle, in-turn allowing for more confident reconstructions of Earth’s past ocean oxygenation using Tl isotopes. This research will be led by a postdoctoral investigator and will further the education of several undergraduate summer interns. K-12 outreach efforts associated with this research will introduce students and teachers in the greater Boston area to biogeochemistry and Earth science. Measurements of Tl isotope ratios in ancient marine sedimentary rocks have rapidly accelerated over the past half-decade because there is reason to think they can track changes in past ocean oxygenation. Unfortunately, the modern Tl isotope investigations necessary to guide and hone interpretations have not kept pace with the ancient applications. The PIs’ preliminary data from a redox-stratified and brackish pond (Siders Pond, Cape Cod) show that it is feasible, even under very low Tl concentrations, to generate quality Tl isotope data for waters, particles, and sediments in a natural setting. Moreover, these preliminary data identify a strong and temporally dynamic link connecting Tl isotopes to local manganese (Mn) oxide cycling. These results highlight the direct role that Mn oxide minerals – and not O2 – play in driving Tl isotope fractionation effects. The PIs are proposing to expand their Tl isotope investigation of Siders Pond, and also to target two additional geochemically distinct freshwater settings in Minnesota (Deming and Steel lakes). Guided by the preliminary data, the PIs predict that Tl isotope cycling in these additional settings will also be most directly coupled to local Mn cycling, with comparatively little to no effects being driven by other Tl interactions. Objectives guiding this research are (1) to better understand and quantify how Tl and its isotopes are partitioned between waters and particles under different redox conditions, and (2) to better understand and quantify how Tl and its isotopes are retained in sediments under different redox conditions. These objectives will be addressed via a combination of fieldwork, trace metal and isotope ratio measurements, and synchrotron-based techniques. An improved understanding of modern Tl isotope cycling will only serve to strengthen interpretations of ancient sedimentary Tl isotope ratios – and their connections to past ocean oxygenation.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.

元素铊（Tl）作为重建地球古代海洋中分子氧（O2）历史的工具正在获得动力。重建这段历史很重要，因为地球古代海洋中氧气的可用性在我们星球上生命的起源和进化中发挥了关键的控制作用。此外，现代海洋正在进行的脱氧将影响到地球上的每一个人，如果我们了解地球过去的类似事件，我们可以更好地预测和准备这种脱氧。Tl追踪海洋O2变化的效用源于其同位素通过与锰（Mn）氧化物矿物的相互作用而强烈分馏的事实，锰（Mn）氧化物矿物形成并埋藏在今天仅存在O2的海洋沉积物中。事实上，许多研究表明，保存在古代海洋岩石中的Tl同位素比率可以提供有关海洋中过去O2可用性的重要信息。然而，我们对现代Tl同位素循环的理解还远未完成，这主要是由于在当今环境中发现的Tl的丰度极低，这使得难以收集足够的材料用于精确的Tl同位素分析。PI在科德角（赛德斯池塘）的半咸水池塘中的初步工作表明，在铊丰度非常低的环境中生成水、颗粒和沉积物的高质量铊同位素数据是可行的。此外，这项工作的早期结果提供了有关Tl同位素与Mn氧化物的联系以及Mn氧化物与O2联系的重要新信息，这些联系可能也存在于古代海洋环境中。这是PI '计划升级他们的工作在赛德斯池塘，并扩大到两个淡水湖在明尼苏达州（德明和钢湖）。这项工作的结果将大大提高我们对现代铊同位素循环的理解，从而使我们能够使用铊同位素更有信心地重建地球过去的海洋氧合。这项研究将由博士后研究员领导，并将进一步教育几个本科暑期实习生。与这项研究相关的K-12外展工作将向大波士顿地区的学生和教师介绍地球化学和地球科学。在过去的五年里，对古代海洋沉积岩中铊同位素比率的测量迅速加速，因为有理由认为它们可以跟踪过去海洋氧化的变化。不幸的是，指导和磨练解释所必需的现代铊同位素研究没有跟上古代应用的步伐。PI的初步数据从氧化还原分层和半咸水池塘（赛德斯池塘，科德角）表明，它是可行的，即使在非常低的铊浓度，以产生高质量的铊同位素数据的沃茨，颗粒和沉积物在自然环境中。此外，这些初步的数据确定了一个强大的和时间动态的链接连接Tl同位素的本地锰（Mn）氧化物循环。这些结果突出了锰氧化物矿物-而不是O2 -在驱动Tl同位素分馏效应中发挥的直接作用。PI建议扩大他们的锡同位素调查赛德斯池塘，并针对两个额外的地球化学不同的淡水设置在明尼苏达州（德明和钢湖）。在初步数据的指导下，PI预测在这些额外的设置中的Tl同位素循环也将最直接地耦合到局部Mn循环，相对较少或没有影响由其他Tl相互作用驱动。本研究的目的是（1）更好地理解和量化不同氧化还原条件下铊及其同位素在沃茨和颗粒之间的分配;（2）更好地理解和量化不同氧化还原条件下铊及其同位素在沉积物中的保留。这些目标将通过实地考察，微量金属和同位素比测量，同步加速器为基础的技术相结合来解决。对现代铊同位素循环的更好理解只会有助于加强对古代沉积铊同位素比率的解释-以及它们与过去海洋氧化的联系。该奖项反映了NSF的法定使命，并被认为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来支持。

项目成果

Water properties of Arco Lake, Budd Lake, Deming Lake, and Josephine Lake in Itasca State Park from 2006-2009 and 2019-2021, v. 2.

2006-2009 年和 2019-2021 年艾塔斯卡州立公园阿科湖、巴德湖、戴明湖和约瑟芬湖的水特性，v. 2。

• DOI: 10.6073/pasta/692c92ef1c8291162732c2b98cebdaea
• 发表时间: 2022
• 期刊: Environmental Data Initiative
• 作者: Swanner, Elizabeth D;Lascu, Ioan;Ledesma, Gabrielle;Leung, Tania;Akam, Sajjad
• 通讯作者: Akam, Sajjad