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

海洋中的生命常常受到营养物质的限制，如氮和磷。其他丰度低得多的元素也是生物必需的，可能是限制性的，尤其是微量金属，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氧气水平密切相关；大陆的风化作用；不断变化的大气成分；还有生物进化。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的研究，但由于对某些化学方法的试验不足，特别是在现代海洋中，我们的知识仍然存在基本差距。这些方法一旦得到改进，就可以更有信心地探索地球表面过去的大量情况——远远超过今天所看到的情况。从这个强化的优势，研究人员可以开始更严格和全面地想象我们的未来。在地球不断演变的海洋中进行“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。黄铁矿是一种如今和过去都很常见的硫化铁矿物，它可以提供易于获取和高度保存的历史档案。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，但在目前的环境条件（当地和全球）可以直接与矿物成分联系在一起的现代海洋中，以前没有人试图验证和校准黄铁矿示踪剂。这项研究是现代系统中这些关系的第一次全面调查，通过有针对性的实验和新的分析技术得到加强。主要的预期结果是提高对地球表面变化的控制和后果的理解，这些变化表现在海洋化学的演变中——过去、现在和未来——以及与共同进化的生命的因果关系。许多研究现在使用一种叫做激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）的技术来测量黄铁矿的痕量金属含量，作为过去海洋条件的示踪剂，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不同的环境梯度中变化，人们仍然知之甚少。这些不确定性削弱了它们的效用。局部控制和捕获潜在的全球信号之间的关系在很大程度上仍然未知。因此，本研究围绕双管齐下的方法进行设计：(1)在五个经典的、研究充分的现代海洋环境中取样，这些环境具有良好的原始环境条件的多样性；(2)互补的、精心构思的实验室模拟，旨在为硫化铁矿物对微量金属的吸收机制及其对环境背景的敏感性提供前所未有的见解。最终目标是揭示代理和最佳做法的优缺点，同时揭示新的机会，例如跟踪古代深层生物圈中生物必需微量金属的可用性的可能性。计划包括分析现代海洋中不同环境下的孔隙水和沉积物，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随周围环境的条件而变化。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，应用于高分辨率来表征实验和自然样品。这将是第一个将黄铁矿金属含量与周围流体中金属可用性联系起来的系统研究，并将这些数据更广泛地与地球古代生物圈研究中经常包括的各种环境参数和代用物联系起来。这项研究的影响将通过针对里昂实验室的初高中学生和UCR本科生的外展机会广泛扩展，同时在各个层面倡导多样性和包容性。该社区的足迹将通过定期的公共讲座系列和一个完全用西班牙语呈现的校园科学节，以及其他已经经过测试的社区指导的努力来扩大。在CMU，计划包括在弗林特（密歇根州）的两所中学进行地球化学研究，强调水质，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。

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.