EAR-PF: Controls of and connections between silicate weathering and organic carbon cycling in watersheds: A test case in the Upper Deschutes Basin, Oregon, USA

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。Evan J. Ramos博士获得了美国国家科学基金会EAR博士后奖学金，在莱斯大学和布朗大学分别接受Mark A. Torres和Daniel E. Ibarra教授的指导，进行研究、专业发展和外展活动。该项目研究了美国俄勒冈州喀斯喀特山脉流域的硅酸盐风化、有机碳（OC）循环及其潜在耦合的性质。土壤中的硅酸盐风化和OC循环影响固体地球与地球海洋和大气之间CO2的转移，从而迫使并响应一系列时间尺度上的气候变化。众所周知，这些过程是相互影响的，但如果没有工具可以同时定量地探测这两个过程，我们了解硅酸盐风化或OC循环如何响应过去的气候变化或它们将如何响应未来的能力是非常有限的。该项目的目标是开发一种多代理地球化学方法，允许在跨越数千年至数百万年的时间尺度上对硅酸盐风化和OC循环进行双重分析。在夏威夷土壤年龄序列中，已公布的土壤锂（Li）同位素组成（硅酸盐风化强度的量度）与土壤OC浓度之间存在显著的负相关，拉莫斯博士将通过以下方法来测试这些综合测量的适用性：(1)测量具有不同于夏威夷的环境和地质条件的分水岭土壤和河流沉积物中的Li同位素组成和OC浓度；(2)开发模拟土壤中硅酸盐风化和OC循环的模型。研究和专业发展将包括对莱斯大学和布朗大学的一名本科生进行样本采集、土壤地球化学分析、模型开发以及书面和口头科学交流方面的培训。项目结果将被纳入生态系统和流域的虚拟实地体验，与此虚拟实地体验相关的课程计划将与休斯顿地区的科学教育者一起开发，用于初中和高中科学课程。土壤中的硅酸盐风化和有机碳（OC）循环在数千年到数百万年的时间尺度上响应和影响气候。虽然通常是相互独立的研究，但硅酸盐风化和有机碳循环都是通过土壤中养分、酸和活性表面的预算密切相关的。结果是一组复杂的正反馈和负反馈，这使得预测风化或OC循环如何响应环境变化变得困难。此外，风化作用和有机碳循环之间的关系不一定是相同的，而是可能被不同景观元素（如山地、山坡、洪泛平原）上的物理过程所改变。拉莫斯博士将测试这样一个假设，即在千年的时间尺度上，硅酸盐风化和有机碳储存是通过相互依赖于层状硅酸盐（粘土）矿物形成的速率而正耦合的，因此，有利于粘土矿物形成的景观元素（例如，洪积平原）强烈影响二氧化碳的净排放量。该项目将包括对河流沉积物、土壤和基岩进行采样，并随后测量从高地到洪泛平原过渡的Li同位素比率、OC含量和放射性碳（14C）含量，以进一步了解无机碳和有机碳耦合循环。俄勒冈瀑布的上德舒特盆地提供了一个令人信服的环境来收集关键数据，以验证我们的假设，因为它的岩性（火山）均匀性，地质新近形成（6.8 kya），其地理特征与最近冰川消退的地形上的其他水源集水区相似。此外，研究结果将用于开发一个通用模型，以解决现代风化预算中突出的不一致性，以及由于地质时期景观形式的变化而导致的长期C旋回变化的潜在幅度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. Evan J. Ramos has been awarded an NSF EAR Postdoctoral Fellowship to conduct research, professional development, and outreach activities at Rice University and Brown University under the mentorship of Professors Mark A. Torres and Daniel E. Ibarra, respectively. This project investigates the nature of silicate weathering, organic carbon (OC) cycling, and their potential couplings across a watershed in the Cascade Mountains of Oregon, USA. Silicate weathering and OC cycling in soils influence the transfer of CO2 between the solid Earth and Earth’s ocean and atmosphere, thereby forcing and responding to changes in climate over a range of timescales. These processes are known to influence one another, but without tools to quantitatively probe both simultaneously, our ability to understand how either silicate weathering or OC cycling have responded to past climate change or how they will respond in the future is critically limited. The goal of this project is to develop a multiproxy geochemical approach that allows for the dual analyses of silicate weathering and OC cycling over timescales spanning millennia to millions of years. Motivated by a significant inverse correlation found between published soil lithium (Li) isotope compositions (a measure of silicate weathering intensity) and soil OC concentrations in a soil age sequence in Hawaii, Dr. Ramos will test the applicability of these combined measurements by (1) measuring Li isotope compositions and OC concentrations in soil and river sediments across a watershed with environmental and geologic conditions that differ from Hawaii and (2) developing models that simulate silicate weathering and OC cycling in soils. Research and professional development will involve the training of one undergraduate at Rice and one at Brown in sample acquisition, geochemical analysis of soils, model development, and written and verbal scientific communication. Project findings will be incorporated into a virtual field experience on ecosystems and watersheds, and lesson plans related to this virtual field experience will be developed with Houston-area science educators for usage in middle and high school science classes.Silicate weathering and organic carbon (OC) cycling in soils respond to and affect climate on a range of timescales, from millennia to millions of years. While typically studied independently of one another, both silicate weathering and OC cycling are intimately tied via the budgets of nutrients, acids, and reactive surfaces in soils. The result is a complex set of positive and negative feedbacks that make it difficult to predict how either weathering or OC cycling will respond to environmental change. Moreover, the relationship(s) between weathering and OC cycling need not be the same across a landscape and may instead be modified by the physical processes operating on distinct landscape elements (e.g., mountain hillslopes, floodplains). Dr. Ramos will test the hypothesis that, over millennial timescales, silicate weathering and OC storage are positively coupled through a mutual dependence on the rate of phyllosilicate (clay) mineral formation and that, as a result, landscape elements where clay mineral formation is favored (e.g., floodplains) strongly impact the net amount of CO2 drawdown. This project will involve sampling of river sediments, soils, and bedrock and subsequent measurements of Li isotope ratios, OC contents, and radiocarbon (14C) contents across an upland to floodplain transition to further our understanding of the coupled inorganic and organic C cycles. The Upper Deschutes Basin in the Oregon Cascades offers a compelling setting to gather critical data that test our hypothesis because of its lithologic (volcanic) uniformity, geologically recent formation (6.8 kya), and its physiographic similarity to other headwater catchments in recently deglaciated terrains. Additionally, results will be used to develop a generic model to address outstanding inconsistencies in modern weathering budgets and the potential magnitude of secular C cycle variation due to changing landscape forms over geologic time.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.