Collaborative Research: EAR-Climate: Physical Controls on CO2 Release from Shale Weathering

合作研究：EAR-气候：页岩风化中二氧化碳释放的物理控制

• 批准号: 2141519
• 负责人: Joel Scheingross
• 金额: $ 37.85万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2141519&HistoricalAwards=false
• 关键词: Collaborative; Research; EAR; Climate; Physical

Shales, commonly found sedimentary rocks, contain a large amount of organic carbon and have been mined for oil, natural gas, and other fossil fuels. Analogous to how the burning of fossil fuels releases carbon dioxide (CO2) to the atmosphere, the natural weathering of shale also releases CO2. While this CO2 release occurs slowly, it has potential to change Earth’s climate over million-year timescales. The scientific community currently lacks understanding about how shale weathering (and associated CO2 release) occurs, and this limits understanding of both past changes in Earth’s climate and predictions of future changes. This project examines how changes in climate and erosion influence the rate of shale weathering via performing a detailed field study in shale rock exposed throughout California. Field work results will be incorporated into a mathematical model that will allow estimates of the rate of CO2 release from shale weathering across the globe. This project will thus both advance understanding of an important natural control on Earth’s climate, and provide a framework to improve predictions of climate change in the future. In addition to these benefits, the project will also provide training for graduate and undergraduate students and project members will engage in K-8 and community outreach to provide geoscience education. Despite previous work on the chemical and biological processes that drive shale weathering, there does not exist a mechanistic understanding of how physical processes modulate CO2 release from shale weathering. This project addresses this knowledge gap by quantifying how variations in physical erosion rate, precipitation rate, and local topography influence shale weathering. The project tests the hypothesis that feedbacks between the supply of carbon during conversion of rock to regolith, chemical kinetics, and topographic controls on weathering zone thickness cause CO2 release from shale weathering to be maximized for areas with modest erosion rates, modest precipitation rates, and high topographic curvature (i.e., ridges). To accomplish this, the researchers will measure the loss of organic carbon in depth-profiles of shale up to 10 m deep, focusing on shales of the Monterey, Rincon, and Cozy Dell formations in the Santa Ynez Mountains, California, where a 6-fold erosion gradient allows assessment of how variation in erosion influences shale weathering. The Santa Ynez Mountain samples will be supplemented with depth profiles of Monterey Shale from Point Reyes National Seashore and Carrizo Plain, California, allowing exploration of shale weathering over a 5-fold gradient in precipitation within the same lithologic formation. The field data will be used to calibrate and modify a reactive-transport model based on physical forcing, thereby providing new opportunities to link geomorphic transport laws with biogeochemical models, and predict CO2 release from shale weathering across a wide range of spatial and temporal scales. Documenting links between physical processes and silicate weathering has led to major advances in the understanding of feedbacks between climate, tectonics, and topography, and documenting such tradeoffs for shale weathering in this project is a logical, yet critical next step to advance understanding of the geologic carbon cycle.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.

页岩是常见的沉积岩，含有大量的有机碳，已被开采用于石油、天然气和其他化石燃料。与燃烧化石燃料向大气释放二氧化碳(CO2)类似，页岩的自然风化也释放出二氧化碳。虽然二氧化碳的释放速度很慢，但它有可能在一百万年的时间尺度上改变地球的气候。科学界目前对页岩风化(以及相关的二氧化碳释放)是如何发生的缺乏了解，这限制了对地球气候过去变化和对未来变化预测的了解。该项目通过对加州各地暴露的页岩进行详细的实地研究，研究气候和侵蚀的变化如何影响页岩风化的速度。实地工作结果将被纳入一个数学模型，该模型将允许估计全球页岩风化释放二氧化碳的速度。因此，该项目既将促进对地球气候的重要自然控制的理解，也将提供一个框架，以改进对未来气候变化的预测。除了这些好处外，该项目还将为研究生和本科生提供培训，项目成员将参与K-8和社区外联活动，以提供地球科学教育。尽管之前对驱动页岩风化的化学和生物过程进行了研究，但对于物理过程如何调节页岩风化释放的二氧化碳，还没有一个机械上的理解。该项目通过量化物理侵蚀速率、降雨率和局部地形的变化如何影响页岩风化来解决这一知识鸿沟。该项目测试了一种假设，即在岩石向风化层转化过程中碳的供应、化学动力学和地形对风化带厚度的控制之间的反馈，使得在侵蚀速率适中、降水速率适中和地形曲率(即山脊)较高的地区，页岩风化释放的二氧化碳最大。为了实现这一目标，研究人员将测量页岩深度剖面中有机碳的损失，深度可达10米，重点是加利福尼亚州圣伊内斯山脉蒙特雷、Rincon和Cozy Dell地层的页岩，在那里，6倍的侵蚀梯度可以评估侵蚀变化如何影响页岩风化。Santa Ynez山样品将补充来自Point Reyes National Seashore和加利福尼亚州Carrizo Plain的蒙特雷页岩的深度剖面，允许勘探同一岩性地层内超过5倍降水梯度的页岩风化。现场数据将用于校准和修改基于物理强迫的反应迁移模型，从而提供新的机会，将地貌迁移规律与生物地球化学模型联系起来，并在广泛的空间和时间尺度上预测页岩风化释放的二氧化碳。记录物理过程和硅酸盐风化之间的联系在了解气候、构造和地形之间的反馈方面取得了重大进展，并在该项目中记录了页岩风化的这种权衡，这是促进对地质碳循环理解的合乎逻辑的关键下一步。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。