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: 2141520
• 负责人: Mark Torres
• 金额: $ 25.82万
• 依托单位: William Marsh Rice University
• 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=2141520&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。类似于化石燃料的燃烧如何向大气中释放二氧化碳（CO2），页岩的自然风化也会释放CO2。虽然这种二氧化碳释放发生缓慢，但它有可能在数百万年的时间尺度上改变地球的气候。科学界目前缺乏对页岩风化（以及相关的二氧化碳释放）如何发生的理解，这限制了对地球气候过去变化和未来变化预测的理解。该项目通过对整个加州的页岩进行详细的实地研究，考察气候和侵蚀的变化如何影响页岩风化的速率。 现场工作结果将被纳入一个数学模型，该模型将允许估计整个地球仪页岩风化的二氧化碳释放率。因此，该项目将促进对地球气候的重要自然控制的理解，并提供一个框架，以改善对未来气候变化的预测。除了这些好处，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。尽管以前的工作，推动页岩风化的化学和生物过程，有没有一个机械的理解，如何物理过程调制二氧化碳释放页岩风化。该项目通过量化物理侵蚀速率、降水速率和当地地形的变化如何影响页岩风化来解决这一知识缺口。该项目测试了这样一个假设，即岩石向风化层转化过程中碳的供应、化学动力学和风化带厚度的地形控制之间的反馈，导致页岩风化产生的CO2释放在侵蚀速率适中、降水速率适中和地形曲率较高的地区（即，脊）。为了实现这一目标，研究人员将测量10米深的页岩深度剖面中有机碳的损失，重点是加州Santa Ynez山脉Monterey，Rincon和Cozy Dell地层的页岩，其中6倍的侵蚀梯度允许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和加州Carrizo Plain的Monterey页岩深度剖面，允许在同一岩性地层中勘探超过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传输模型，从而提供新的机会，将地貌传输规律与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的CO2释放。记录物理过程和硅酸盐风化之间的联系，使人们对气候、构造和地形之间的反馈的理解取得了重大进展，在本项目中记录页岩风化的这种权衡是合乎逻辑的，这一奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。