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.

铊 (Tl) 元素作为重建地球古代海洋中分子氧 (O2) 历史的工具，正在获得越来越多的发展势头。重建这段历史非常重要，因为地球古代海洋中氧气的可用性在地球上生命的起源和进化中发挥了关键的控制作用。此外，现代海洋持续的脱氧现象将影响地球上的每个人，如果我们了解地球过去发生的类似事件，我们就可以更好地预测这种脱氧现象并为此做好准备。 Tl 用于追踪海洋 O2 变化的用途源于这样一个事实，即它的同位素通过与氧化锰 (Mn) 矿物的相互作用而被强烈分馏，而现在只有 O2 存在的地方才形成并埋藏在海洋沉积物中。事实上，许多研究表明，古代海洋岩石中保存的 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，这主要是由于当今环境中发现的 Tl 丰度极低，这使得收集足够的材料进行准确的 Tl 同位素分析变得困难。 PI 在科德角咸水池塘（Siders Pond）进行的初步工作表明，在铊丰度极低的环境中生成水、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连接铊同位素与锰氧化物以及锰氧化物与 O2 的链接的重要新信息，这些链接可能也存在于古代海洋环境中。 PI 计划扩大其在 Siders Pond 的工作范围，并将其扩展到明尼苏达州的两个淡水湖（戴明湖和斯蒂尔湖）。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，从而使我们能够利用 Tl 同位素更自信地重建地球过去的海洋氧化作用。这项研究将由一名博士后研究员领导，并将进一步促进几名本科生暑期实习生的教育。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铊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铊同位素研究并没有跟上古代应用的步伐。 PI 来自氧化还原层微咸水池塘（科德角的 Siders Pond）的初步数据表明，即使在非常低的 Tl 浓度下，生成自然环境中的水、颗粒和沉积物的高质量 Tl 同位素数据也是可行的。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大的时间动态联系。这些结果强调了锰氧化物矿物（而不是 O2）在驱动 Tl 同位素分馏效应中发挥的直接作用。 PI 提议扩大对 Siders Pond 的 Tl 同位素调查，并针对明尼苏达州另外两个地球化学特征不同的淡水环境（戴明湖和斯蒂尔湖）。在初步数据的指导下，PI 预测这些额外环境中的 Tl 同位素循环也将最直接地与局部 Mn 循环相关，而其他 Tl 相互作用驱动的影响相对较小甚至没有。指导这项研究的目标是（1）更好地了解和量化不同氧化还原条件下铊及其同位素如何在水和颗粒之间分配，以及（2）更好地了解和量化不同氧化还原条件下铊及其同位素如何保留在沉积物中。这些目标将通过现场工作、痕量金属和同位素比测量以及基于同步加速器的技术相结合来实现。提高对现代 Tl 同位素循环的理解只会有助于加强对古代沉积 Tl 同位素比率及其与过去海洋氧化的联系的解释。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。

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