Digging into Soil Carbonate Formation Processes with Triple Oxygen Isotopes

该奖项全部或部分根据2021年美国救援计划法案（公法117-2）资助。旱地是水资源有限的生态系统，覆盖地球陆地表面的40%，是25亿人的家园，特别容易受到气候变化的影响。碳酸盐形成的土壤在旱地生态系统中很常见，是碳循环的重要组成部分，对建立过去气候记录至关重要，但我们并不完全了解它们是如何形成的。本项目将调查土壤水分流失作为土壤碳酸盐形成机制的作用。研究小组将使用氧的三种稳定同位素16 O、17 O和18 O来区分土壤水分通过蒸发流失与植物吸收的作用。虽然氧同位素18 O与16 O的比值通常用于研究土壤碳酸盐和其他气候档案，但第三稳定氧同位素17 O的丰度要低得多，并且尚未完全开发用于土壤和过去气候的研究。该项目将开发三重氧同位素分布（比较所有三种氧同位素）作为工具，通过在美国主要生态和干旱梯度的实地工作，研究现代和古代气候中的土壤形成过程，包括旱地临界区网络中的地点。这项工作的结果将改善过去气候的重建，特别注意检测古代生态系统中的干旱和干旱。该项目将为博士后科学家提供培训，为建立自己的分析密集型实验室和研究计划做准备，满足对更多实验室和PI的需求，这些实验室和PI能够进行具有分析挑战性的三重氧同位素测量。在三个机构培训本科生将是本研究实地组成部分不可或缺的一部分。这项工作的本科生部分将扩大地球科学的参与，包括通过密歇根大学地球营计划招募参与者。由于现代气候变化，水文循环的变异性增加，可能会导致水和碳储存的反馈。与此同时，现代气候变化增强了对工具的需求，以确定古代气候中的水压力，作为我们未来世界的类似物。该项目使用三重氧同位素来评估在美国土壤碳酸盐形成过程中蒸发和蒸腾在土壤脱水中的作用。这项工作将包括对土壤中碳酸盐及其母源大气沃茨中三重氧同位素的研究。我们的实地工作将集中在美国的四个地点，包括加州的超干旱莫哈韦沙漠，密歇根州的半湿润落叶林，以及两个干旱环境中的中间地点，爱达荷州的雷诺兹溪和新墨西哥州的Jornada盆地。 这项工作的成果将包括消除蒸发对成土碳酸盐三角洲18 O影响的工具，以揭示大气降水三角洲18 O，这是古水文学和古高度测量学的圣杯。这项工作将提高我们对非生物和生物过程如何各自控制成土碳酸盐形成的理解;这种理解是必要的，以便能够预测在预测的增加的水文变化下，成壤碳酸盐将如何以及在何处沉淀在自然和农业土壤中，该奖项反映了NSF的法定使命，并被认为是值得的。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，

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Drylands are water-limited ecosystems that cover 40% of Earth's land surface, are home to 2.5 billion people, and are particularly vulnerable to climate change. Carbonate-forming soils, which are common in dryland ecosystems, are important components to the carbon cycle and critical for building records of past climate, but we do not fully understand how they form. This project will investigate the role of water loss from soils as a mechanism for soil carbonate formation. The team will use the three stable isotopes of oxygen, 16O, 17O and 18O, to distinguish between the role of soil water loss via evaporation vs. uptake by plants. While ratios of oxygen isotopes 18O to 16O are commonly used to study soil carbonate and other climate archives, 17O, the 3rd stable oxygen isotope, is far less abundant and has not been fully developed for studies of soils and past climate. This project will develop triple oxygen isotope distributions (comparing all three oxygen isotopes) as tools for investigating soil formation processes in modern and ancient climates through field work across major ecological and aridity gradients in the U.S., including sites in the Drylands Critical Zone Network. The results from this work will improve reconstructions of past climate, with particular attention to detecting drought and aridity in ancient ecosystems. The project will provide training for a postdoctoral scientist in preparation for building her own analytically intensive laboratory and research program, filling the need for more laboratories and PIs who are capable of making analytically challenging triple oxygen isotope measurements. Training of undergraduates at three institutions will be integral to the field components to this research. The undergraduate component to this work will broaden participation in the geosciences and include recruiting participants through the University of Michigan Earth Camp program.Increased variability in the hydrologic cycle due to modern climate change will potentially lead to feedbacks in water and carbon storage. At the same time, modern climate change enhances the need for tools to identify water stress in ancient climates as analogues for our future world. This project uses triple oxygen isotopes to evaluate the role of evaporation and transpiration in soil dewatering during soil carbonate formation in the U.S. This work will include a study of triple oxygen isotopes in carbonate in soils and in their parent meteoric waters. Our field work will focus on four sites in the US that include the hyper-arid Mojave Desert of California, the subhumid deciduous forest in Michigan, and two intermediate sites in arid environments, Reynolds Creek, Idaho and the Jornada Basin in New Mexico. The outcomes of this work will include tools for stripping away the effects of evaporation on pedogenic carbonate delta 18O to reveal meteoric water delta 18O, which is the holy grail for paleohydrology and paleoaltimetry. This work will improve our understanding of how abiotic and biotic processes each control pedogenic carbonate formation; this understanding is necessary to be able to predict how and where pedogenic carbonate will precipitate in natural and agricultural soils under the predicted increased hydrological variability, with implications for carbon sequestration and water storage in dryland critical zones.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.