CAREER: Understanding past and present biogeochemical cycle of potassium (K) and its implications for the global carbon cycle: proxy development based on stable K isotopes

硅酸盐岩石的风化作用是地球天然“恒温器”的重要组成部分。硅酸盐风化可以将二氧化碳从大气中清除出去，被认为是一种自然反馈，可以对抗全球气温的上升，从而保持适宜居住的气候。硅酸盐岩石中钾（K）同位素的分析与了解过去硅酸盐风化速率密切相关。然而，最近的研究表明，从硅酸盐风化的副产品中形成新的硅酸盐粘土矿物可能会逆转硅酸盐风化的化学反应，从而使该过程在冷却地球方面的效果降低。从副产品中形成粘土，这一过程被称为“逆风化”，研究起来很有挑战性，因为它发生在深海的偏远地区，反应速度很慢。因此，这在我们对影响我们对过去，现在和未来气候的长期硅酸盐和碳循环的理解方面存在根本性的知识差距。该项目开发了稳定的钾同位素作为一种新的替代物或示踪剂，以帮助量化现代和过去的硅酸盐风化速率。通过分析地球物质中的钾同位素，研究现代和过去的钾循环及其与硅酸盐风化和全球碳循环的关系。这项研究将量化海洋钾同位素的变化，有助于对海洋粘土形成的全球意义及其对气候的影响提供可靠的估计。该项目通过一个综合的研究和教育计划，（1）支持地球化学基础设施，以完成大学的研究和教育任务;（2）为本科生和研究生提供实验室培训，同时沿着中小学生的教育机会;（3）将现代化的地球化学实验室扩展到校园之外，以吸引和建立地球化学相关领域的多元化劳动力;以及（4）提高公众对地球化学研究的社会意义以及对我们星球的环境和气候的认识。该研究旨在促进对海洋稳定钾（K）同位素循环的理解，以开发一个可靠的硅酸盐风化代用指标。该项目采用受控实验室实验和对有目的地选择的天然海洋样品的分析，以限制现代海洋钾同位素循环中的关键不确定性，包括海水-玄武岩蚀变和粘土形成过程中的钾同位素分馏。同位素质量平衡模型正被用于定量估计当今粘土形成或逆风化的全球意义。此外，实验室实验，辅以光谱表征和建模方法，将推进知识钾同位素交换动力学和分馏有关的海水钾同位素组成的衍生相关的地质档案，如海洋碳酸盐岩。可行性包括制定一个解释框架，使地质档案能够用于重建古海洋中的钾同位素特征，并评估其对长期碳循环的影响。通过研究与教育的结合，该项目推进了钾同位素的跨学科研究，并将开发工具的应用扩展到气候变化背景下复杂的植物-土壤-气候反馈。该奖项反映了NSF的法定使命，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。

The weathering of silicate rocks is an important part of Earth’s natural “thermostat.” Silicate weathering can scrub carbon dioxide out of the atmosphere and is considered a natural feedback that can counter the rise in global temperatures, thus maintaining a habitable climate. The analysis of the potassium (K) isotopes in silicate rocks has been closely linked to understanding past silicate weathering rates. However, recent research suggests that formation of new silicate clay minerals from the byproducts of silicate weathering may reverse the chemical reactions of silicate weathering thus making the processes less effective in cooling the planet. The formation of clays from byproducts, a process termed “reverse weathering”, is challenging to study as it occurs in remote sectors of the deep ocean and the reaction rates are slow. Thus, this presents a fundamental knowledge gap in our understanding of the long-term silicate and carbon cycles impacting what we know about past, present, and future climate. This project develops stable potassium isotopes as a novel proxy, or tracer, to help quantify modern and past silicate weathering rates. Via analyzing potassium isotopes in Earth materials, this project investigates the modern and past potassium cycle and its relationship to silicate weathering and the global carbon cycle. The study will quantify changes in marine potassium isotopes, helping to provide robust estimates on the global significance of marine clay formation and its impact on climate. Through a comprehensive plan integrating research and education, this project (1) supports geochemistry infrastructure to fulfill research and education missions of the university; (2) provides laboratory training for undergraduate and graduate students along with educational opportunities for primary and secondary students; (3) extends accessibility of a modern geochemical laboratory beyond the campus boundary to attract and build a diversified workforce in geochemistry-related fields; and (4) raises public awareness of the societal relevance of geochemistry research and of the environment and climate of our planet.The research aims to advance understanding of the marine stable potassium (K) isotopic cycle to develop a robust proxy for silicate weathering. This project applies controlled laboratory experiments and analysis of purposefully selected natural marine samples to constrain key uncertainties in the modern marine potassium isotopic cycle, including potassium isotope fractionation during seawater–basalt alterations and clay formation. Isotope mass balance models are being applied to quantitatively estimate the global significance of present-day clay formation or reverse weathering. Additionally, laboratory experiments, supplemented by spectroscopic characterization and a modeling approach, will advance knowledge on potassium isotope exchange kinetics and fractionation pertinent to derivation of seawater potassium isotope compositions from relevant geologic archives such as marine evaporites. Deliverables include development of an interpretative framework that will enable the use of geological archives to reconstruct potassium isotope signatures in ancient oceans and to assess their implications to the long-term carbon cycle. Through the integration of research and education, this project advances interdisciplinary research in potassium isotopes and expands application of the developing tool to the complex plant–soil–climate feedbacks in the context of changing climate.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.