Collaborative Research: Trace Elements in Pyrite—Validation and Calibration of a Novel Paleoenvironmental Proxy

海洋中的生命往往受到氮和磷等营养物质的限制。其他元素的丰度要低得多，也是生物必需的，并可能限制，特别是微量金属，如铁和钼。这些金属是许多生物过程中的辅助因素，它们在时间和空间上的分布与海洋中的含氧量、大陆的风化、不断变化的大气成分和生物进化密切相关。所有这些因素都与气候变化密切相关，气候变化是陆地和海洋金属循环的关键驱动因素和后果。然而，尽管对现代和古代海洋中的金属进行了广泛研究，但由于某些化学方法测试不足，特别是在现代海洋中，我们的知识仍然存在基本空白。这些方法，一旦完善，将允许更有信心地探索地球表面的大量过去条件-远远超出今天所看到的。从这种强化的Vantage出发，研究人员可以开始更严格、更全面地想象我们的未来。通过地球不断演变的海洋进行“时间旅行”的最有希望的方法之一是对黄铁矿进行元素分析，黄铁矿是一种在今天和过去都很常见的硫化铁矿，可以提供易于访问和高度可重复的历史档案。 令人惊讶的是，尽管这种方法可能具有优势，并且已经取得了成功的迹象，但以前没有任何努力试图在现代海洋中验证和校准黄铁矿示踪剂，其中目前的环境条件，当地和全球，可以直接与矿物的组成联系在一起。通过有针对性的实验和新的分析技术得到加强。主要的预期成果是更好地理解地球表面变化的控制和后果，如过去、现在和未来不断演变的海洋化学所表现的那样，以及与共同进化的生命的因果关系。利用LA-ICP-MS技术测量黄铁矿中微量金属含量，作为过去海洋环境的示踪剂，初步结果令人鼓舞。也就是说，对于微量元素如何以及何时被纳入黄铁矿以及这些模式和控制如何在环境梯度中变化，仍然没有什么机械的理解。这些不确定性削弱了它们的效用。局部控制与潜在全球信号捕获之间的关系在很大程度上仍然未知。因此，本研究围绕两个方面进行设计：（1）在五个经典的，经过充分研究的现代海洋环境中进行采样，主要环境条件具有良好的特征多样性;（2）互补的，精心构思的实验室模拟，旨在为铁硫化物矿物的微量金属吸收机制及其对环境背景的敏感性提供前所未有的见解。最终目标是揭示代用品和最佳做法的优缺点，同时揭示新的机会，例如追踪古代深层生物圈中生物必需微量金属的可能性。计划包括分析现代海洋不同环境中的孔隙沃茨和沉积物，并在实验结果的框架内解释这些数据，以揭示痕量金属含量如何与周围环境的条件成比例。该方法的实用性将进一步探索使用新的，高度复杂的分析方法，适用于高分辨率的实验和自然样品的特点。这将是第一个系统的研究，相关的黄铁矿金属含量与周围流体中的金属可用性，并将这些数据更广泛地涉及到广泛的环境参数和代理人往往包括在地球的古代生物圈的研究。这项研究的影响将通过针对里昂实验室的初中和高中学生以及UCR本科生的外展机会广泛扩展，同时倡导各级的多样性和包容性。这一社区足迹将通过一个经常性的公开讲座系列和一个完全用西班牙语举办的校园科学节，以及其他已经经过测试的社区导向的努力来扩大。CMU的计划包括在弗林特（密歇根州）的两所中学进行一项地球化学研究，重点是水质，并利用这些数据为弗林特建立一个新的、急需的社区驱动的水质数据库。该奖项反映了NSF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。

Life in the oceans is often limited by the availability of nutrients, such as nitrogen and phosphorus. Other elements occurring in far lower abundances are also bioessential and potentially limiting—particularly trace metals such as iron and molybdenum. These metals are co-factors in many biological processes, and their distributions through time and space are strongly coupled to oxygen levels in the oceans; weathering of the continents; evolving atmospheric composition; and biological evolution. All of these factors tie intimately to climate change as a critical driver and consequence of metal cycling on land and in the oceans. Yet, despite extensive study of metals in modern and ancient oceans, basic gaps remain in our knowledge because of inadequate testing of certain chemical methods, particularly in the modern oceans. These methods, once refined, would allow for more confident exploration of a vast array of past conditions at Earth’s surface—far beyond those seen today. From that reinforced vantage, researchers can begin to imagine more rigorously and comprehensively what may lie in our future. One of the most promising methods for ‘time travel’ through Earth’s evolving oceans is elemental analysis of pyrite, an iron sulfide mineral common today and in the past that may provide easily accessible and highly preservable historical archives. Surprisingly, despite the advantages that may lie with this approach and hints of success already, no previous effort has attempted to validate and calibrate the pyrite tracer in modern oceans where present environmental conditions, local and global, can be tied directly to the composition of the mineral. This study is the first comprehensive investigation of these relationships in modern systems, strengthened by targeted experiments and novel analytical techniques. The principal expected outcome is an improved understanding of the controls and consequences of change at Earth’s surface as expressed in evolving ocean chemistry—past, present, and future—and the cause-and-effect relationships with co-evolving life.Many studies are now using a technique called laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to measure trace metal contents of pyrite as a tracer for past marine conditions, and the initial results are encouraging. That said, there is still little mechanistic understanding of how and when trace elements are incorporated into pyrite and how these patterns and controls vary across environmental gradients. These uncertainties weaken their utility. The relationships among local controls and the capture of potentially global signals remain largely unknown. Thus motivated, this study is designed around a two-pronged approach: (1) sampling in five classic, well-studied modern marine environments with a well characterized diversity of primary environmental conditions and (2) complementary, carefully conceived laboratory simulations designed to provide unprecedented insight into the mechanisms of trace metal uptake by iron sulfide minerals and their sensitivity to environmental backdrops. The ultimate goal is to expose the strengths and weaknesses of the proxy and best practices while revealing new opportunities, such as the possibility of tracking the availability of bioessential trace metals in the ancient deep biosphere. Plans include analyzing pore waters and sediments from diverse settings in modern oceans and interpreting those data within the framework of experimental results to reveal how trace metal content scales with conditions in the surrounding environment. The utility of the approach will be explored further using novel, highly sophisticated analytical methods applied at high resolution to characterize experimental and natural samples. This will be the first systematic study that correlates pyrite metal contents with metal availability in surrounding fluids and relates such data more generally to the wide range of environmental parameters and proxies often included in studies of Earth’s ancient biosphere. The impacts of this study will extend broadly through outreach opportunities targeting middle and high school students and UCR undergraduates placed in the Lyons lab, while championing diversity and inclusion at all levels. That community footprint will be expanded through a recurring public lecture series and an on-campus science festival presented entirely in Spanish, among other already tested community-directed efforts. At CMU, plans include a geochemical study at two middle schools in Flint (MI) emphasizing water quality and use of those data to construct a new, much-needed community-driven water quality database for Flint.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.