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、向陆地和水生生态系统供应关键营养物质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总的化学风化速率的重要控制，因此，水的运动与地下化学反应之间的联系不仅对于了解地球的历史，而且对于了解地球系统将如何应对未来的气候和人为变化至关重要。然而，目前的模型不能预测从景观中观察到的溶解溶质的输出。为了解决这个问题，该项目将使用实地研究和反应输运模拟相结合的方法，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-排放关系和由此产生的化学通量，(2)风化反应和流体混合对水的稳定和放射性同位素组成的影响，以及(3)在地质时间尺度上控制全球范围的化学风化速率并进而影响大气二氧化碳水平的“水文恒温器”的运行情况。对后者的评价是该项目的首要目标，它有可能提供有关地球历史上最深刻的特征之一--长期温度稳定--背后的机制的新信息。来自不同背景和不同水平的学生将在项目过程中受益于实地测量、数据合成和数值建模。反应输运方法是了解地球环境化学演化的有力工具。然而，尽管反应性运输方法在工业和研究中被广泛使用，但在研究生院或研究生院水平或以上的这一领域的专业培训机会很少。该项目的一个主要教育目标是通过在斯坦福大学为来自广泛的美国机构的研究生、博士后研究员和教师提供关于反应性运输的年度短期课程，来建立对反应性运输方法和模型的坚实的概念性理解。本课程将介绍关键的反应运输概念及其在生物地球化学系统中的应用，从而提供进入该领域的切入点，并接触到越来越多的使用和开发这些模型的人。每年，该课程都会有几位讲师，让学员有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，我研究小组的研究生将在继续发展和改进这门课程方面发挥关键作用，获得教师经验，这些经验将延续到他们未来的职业生涯。

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.