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，正获得越来越多的动力。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起着关键的控制作用。此外，现代海洋正在进行的脱氧将影响地球上的每一个人，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用于追踪海洋O2变化的效用源于这样一个事实，即它的同位素通过与锰（Mn）氧化物矿物的相互作用而强烈分馏，锰（Mn）氧化物矿物今天仅在存在O2的海洋沉积物中形成和埋藏。事实上，许多研究表明，保存在古代海相岩石中的Tl同位素比率可以提供关于过去海洋中氧气可用性的重要信息。然而，我们对现代Tl同位素循环的理解还远远不够完整，这主要是由于当今环境中发现的Tl丰度极低，这使得难以收集足够的材料进行准确的Tl同位素分析。PIs在科德角（Siders pond）一个咸淡水池塘的初步工作表明，在一个Tl丰度非常低的环境中，对水、颗粒和沉积物产生高质量的Tl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氧化物连接的重要新信息，以及Mn氧化物与O2连接的重要新信息，这些连接可能也存在于古代海洋环境中。PIs计划将他们在Siders Pond的工作升级，并将其扩展到明尼苏达州的两个淡水湖（Deming和Steel湖）。这项工作的结果将极大地提高我们对现代Tl同位素循环的理解，进而允许使用Tl同位素更自信地重建地球过去的海洋氧合。这项研究将由一名博士后研究员领导，并将进一步教育几名本科生暑期实习生。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生物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Tl同位素比率的测量迅速加速，因为有理由认为它们可以追踪过去海洋氧合的变化。不幸的是，指导和完善解释所必需的现代Tl同位素研究并没有跟上古代应用的步伐。PIs从氧化还原层状咸淡水池塘（科德角Siders池塘）获得的初步数据表明，即使在非常低的Tl浓度下，也可以在自然环境中为水、颗粒和沉积物生成高质量的Tl同位素数据。此外，这些初步数据确定了Tl同位素与局部锰（Mn）氧化物循环之间存在强烈的、时间动态的联系。这些结果突出了锰氧化物矿物在驱动Tl同位素分馏效应中的直接作用，而不是O2。pi计划扩大他们对Siders池塘的Tl同位素调查，并将明尼苏达州另外两个地球化学上不同的淡水环境（Deming湖和Steel湖）作为目标。在初步数据的指导下，pi预测这些附加环境中的Tl同位素循环也将最直接地与局部Mn循环耦合，其他Tl相互作用驱动的影响相对较小或没有影响。指导本研究的目的是：(1)更好地了解和量化不同氧化还原条件下Tl及其同位素在水体和颗粒之间的分配情况；(2)更好地了解和量化不同氧化还原条件下Tl及其同位素在沉积物中的保留情况。这些目标将通过实地考察、痕量金属和同位素比值测量以及基于同步加速器的技术相结合来实现。对现代Tl同位素循环的更好理解只会有助于加强对古代沉积Tl同位素比率的解释——以及它们与过去海洋氧合作用的联系。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

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