CAREER: A Hydrologic Thermostat for the Global Carbon Cycle?

矿物的化学风化减缓了大气中二氧化碳的浓度、陆地和水生生态系统关键营养物质的供应以及自然产生的污染物的释放。因此，化学风化是地球系统的重要组成部分。水在土壤和山坡中的运动是对整体化学风化速率的重要控制，因此，水的运动和地下化学反应之间的联系不仅对了解地球的历史至关重要，而且对了解地球系统如何应对未来的气候和人为变化也至关重要。然而，目前的模型不能预测所观察到的出口溶解溶质景观。 为了解决这一问题，本项目将结合实地研究和反应输运模拟方法，以确定（1）化学反应和溶质输运速率之间的竞争如何决定河流中的浓度-排放关系以及由此产生的化学通量，（2）风化反应和流体混合对沃茨稳定和放射性同位素组成的影响，以及（3）一个“水文恒温器”的运作，它控制着全球范围的化学风化速率，并通过扩展大气中二氧化碳的水平，在地质时间尺度上。 对后者的评价是该项目的首要目标，它有可能提供关于地球历史上最深刻的特征之一的机制的新信息：它的长期温度稳定性。来自不同背景和不同层次的学生将受益于项目过程中的现场测量，数据合成和数值建模。反应输运方法是理解地球环境化学演化的有力工具。然而，在这一领域，研究生院一级或研究生院以外的专业培训机会很少，尽管反应性运输方法在工业和研究中得到广泛使用。该项目的一个主要教育目标是通过在斯坦福大学为来自美国各机构的研究生、博士后研究员和教员提供关于反应性运输的年度短期课程，建立对反应性运输方法和模型的坚实概念理解。该课程将作为一个介绍关键的反应传输概念及其应用到地球化学系统，从而将提供一个切入点进入该领域，并获得越来越多的人使用和开发这些模型的社区。 每年的课程将包括几名教师，并为参与者提供一个机会，讨论他们的研究，并收到反馈和建议。这里提出的研究也将作为例子，我的研究小组的研究生将在继续发展和改进课程中发挥关键作用，获得作为教师的经验，这些经验将延续到他们未来的职业生涯中。

The chemical weathering of minerals moderates the concentration of carbon dioxide in the atmosphere, the supply of key nutrients to terrestrial and aquatic ecosystems and the release of naturally occurring contaminants. As such, chemical weathering is a critical component of the Earth system. The movement of water through soils and hillslopes is an important control on overall chemical weathering rates, and the resulting connection between the movement of water and chemical reactions in the subsurface is thus critical for understanding not only Earth's history, but also how Earth's systems will respond to future climatic and anthropogenic changes. However, current models cannot predict the observed export of dissolved solutes from landscapes. To address this problem, this project will use a combination of field studies and reactive transport modeling approaches to determine (1) how the competition between the rates of chemical reactions and solute transport dictates concentration-discharge relationships in rivers and the resulting chemical fluxes, (2) the consequences of weathering reactions and fluid mixing on the stable and radiogenic isotopic composition of waters, and (3) the operation of a 'hydrologic thermostat' that governs global scale chemical weathering rates, and by extension atmospheric carbon dioxide levels, over geologic timescales. Evaluation of the latter is an overarching goal of this project that has the potential to provide new information about the mechanism underlying one of the most profound features of Earth's history: its long-term temperature stability. Students from diverse backgrounds and across different levels will benefit from the exposure to field measurement, data synthesis and numerical modeling during the course of the project. The reactive transport approach is powerful tool for understanding the chemical evolution of Earth's environments. Nevertheless, there are very few opportunities for professional training in this area at or beyond the graduate school level, although reactive transport approaches are widely used in both industry and research. A major educational goal of this project is to build a solid conceptual understanding of reactive transport approaches and models by offering a yearly short-course on reactive transport at Stanford University for graduate students, postdoctoral fellows and faculty from a broad spectrum of U.S. institutions. The course will serve as an introduction to key reactive transport concepts and their application to biogeochemical systems, and will thus provide an entry point into the field and access to a growing community of people that use and develop these models. Each year the course will include several instructors and provide an opportunity for participants to discuss their research and receive feedback and recommendations. The research proposed here will also be featured as examples, and the graduate students from my research group will play key roles in continuing to develop and improve the course, gaining experience as instructors that will carry over into their future careers.