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，含有大量有机碳，可开采石油、天然气和其他化石燃料。与化石燃料的燃烧向大气中释放二氧化碳 (CO2) 类似，页岩的自然风化也会释放二氧化碳。虽然二氧化碳的释放缓慢，但它有可能在数百万年的时间内改变地球的气候。科学界目前对页岩风化（以及相关的二氧化碳释放）如何发生缺乏了解，这限制了对地球气候过去变化的理解和对未来变化的预测。该项目通过对整个加利福尼亚州暴露的页岩进行详细的现场研究，研究气候和侵蚀的变化如何影响页岩风化速率。 现场工作结果将被纳入数学模型中，该模型将能够估计全球页岩风化造成的二氧化碳释放率。因此，该项目将增进对地球气候重要自然控制的理解，并提供一个框架来改进对未来气候变化的预测。除了这些好处之外，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 和社区外展活动，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中二氧化碳的释放还没有一个机械的理解。该项目通过量化物理侵蚀率、降水率和当地地形的变化如何影响页岩风化来解决这一知识差距。该项目测试了这样的假设：岩石转化为风化层期间的碳供应、化学动力学和地形对风化带厚度的控制之间的反馈导致页岩风化中二氧化碳的释放在侵蚀率适中、降水率适中和地形曲率高（即山脊）的地区最大化。为了实现这一目标，研究人员将测量深达 10 m 的页岩深度剖面中有机碳的损失，重点关注加利福尼亚州圣伊内斯山脉的 Monterey、Rincon 和 Cozy Dell 地层的页岩，那里的 6 倍侵蚀梯度可以评估侵蚀变化如何影响页岩风化。圣伊内斯山样品将补充来自雷斯岬国家海岸和加利福尼亚州卡里索平原的蒙特利页岩的深度剖面，从而可以在同一岩性地层内勘探 5 倍降水梯度的页岩风化作用。现场数据将用于校准和修改基于物理强迫的反应输运模型，从而提供将地貌输运规律与生物地球化学模型联系起来的新机会，并预测在广泛的时空尺度上页岩风化所释放的二氧化碳。记录物理过程和硅酸盐风化之间的联系在理解气候、构造和地形之间的反馈方面取得了重大进展，并且在该项目中记录页岩风化的这种权衡是推进对地质碳循环的理解的合乎逻辑但又至关重要的下一步。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，被认为值得支持 标准。