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

职业：了解钾 (K) 过去和现在的生物地球化学循环及其对全球碳循环的影响：基于稳定 K 同位素的代理开发

• 批准号: 2238685
• 负责人: Xinyuan Zheng
• 金额: $ 59.96万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-03-01 至 2028-02-29
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2238685&HistoricalAwards=false
• 关键词: CAREER; Understanding; past; present; biogeochemical

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.

硅胶的风化是地球自然“恒温器”的重要组成部分。硅酸盐风化可以从大气中擦洗二氧化碳，被认为是一种自然反馈，可以应对全球温度的升高，从而保持可居住的气候。对硅胶岩石中钾（K）同位素的分析与了解过去的硅酮风化速率密切相关。然而，最近的研究表明，从硅酮风化的副产品形成新的硅胶矿物质可能会逆转硅树脂风化的化学反应，从而使过程在冷却地球方面的有效性降低。从副产品形成的粘土，这是一个称为“反向风化”的过程，在深海偏远地区进行研究挑战，并且反应速率很慢。这，这在我们对长期有机硅和碳周期的理解中列出了基本知识差距，从而影响了我们对过去，现在和未来气候的了解。该项目将稳定的钾同位素作为一种新颖的代理或示踪剂，以帮助量化现代和过去的硅胶风化速率。通过分析的地球材料钾同位素，该项目研究了现代和过去的钾周期及其与硅酮风化和全球碳循环的关系。该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强有力的估计。通过整合研究和教育的全面计划，该项目（1）支持地球化学基础设施来履行大学的研究和教育任务； （2）为本科和研究生提供实验室培训，并为小学和中学生提供教育机会； （3）将现代地球化学实验室的可及性扩展到校园边界之外，以吸引和建立与地球化学相关的领域的多元化劳动力； （4）提高公众对地球化学研究和我们星球环境和气候的社会相关性的认识。该研究旨在提高人们对海洋稳定钾（K）同位素循环的理解，以开发用于硅胶风化的强大代理。该项目应用了受控的实验室实验和有目的选择的天然海洋样品的分析，以限制现代海洋同位素循环中的关键不确定性，包括在海水 - 盆地变化和粘土形成过程中同位钾分离术。同位素质量平衡模型被应用于定量估计当今粘土形成或反向风化的全球意义。此外，通过光谱表征补充和建模方法补充的实验室实验将促进有关同位素交换动力学动力学和分馏的知识，这些分馏涉及从相关的地质档案（如海洋蒸发物）中衍生出海水同位素同位素的组成。可交付成果包括开发解释性框架，该框架将使地质档案馆在古老的海洋中重建同位素的钾特征，并评估它们对长期碳循环的影响。通过研究和教育的整合，该项目在同位素钾同位素方面进行了跨学科研究，并扩大了在气候变化的情况下，将开发工具的应用扩展到复杂的植物 - 土壤 - 气候反馈中。该奖项反映了NSF的法定任务，并通过使用基金会的知识优点和广泛影响来评估NSF的法定任务，并被视为诚实的支持。