EAR-PF: Clumped and Triple Oxygen Isotopes of Terrestrial Carbonates: New Tools to Estimate Aridity and Precipitation in California During Past Greenhouse Climates

Julia Kelson博士被授予NSF EAR博士后奖学金，在密歇根大学安娜堡分校开展研究和教育活动。该项目研究了气候条件下的水循环，这些气候条件的特点是大气中含有高浓度的温室气体（吸热气体），如二氧化碳。只要大气中温室气体的浓度继续增加，我们就可能在未来气候中观察到更多的蒸发和更多的季节性强降水（雨/雪）。理解这种水文循环强度变化的一种方法是探索古代高二氧化碳气候时期的蒸发和降水记录，例如早期新生代时期（6500万至3000万年前）。本项目将开发一种新的工具，利用古代土壤碳酸盐和软体动物壳来估计蒸发强度。这些古老碳酸盐物质的化学成分包含了形成温度的信息，以及它们赖以生长的雨水/地下水受蒸发影响的程度。因此，这个工具将允许同时估计地球表面温度和干旱。研究者将通过密歇根大学附属的外展项目传达理解古代环境变化的重要性。其中一个项目是地球夏令营，它免费将未被充分代表的高中生带到大学和实地。另一个项目是“女性在数学和工程科学方面更出色”（FEMMES），鼓励女孩探索她们在科学方面的潜力。该项目利用两种新的稳定碳酸盐同位素测量来提高我们重建古代气候干旱和降水的能力。本研究由两个部分组成：1)现代校准研究，测量现代土壤碳酸盐和软体动物壳的同位素组成，以及现代大气水的同位素，以增加对碳酸盐同位素组成如何反映其环境的日益增长的理解；2)应用于古代温室气候；这些新指标被应用于加利福尼亚的古新世剖面，该剖面既有古土壤碳酸盐也有软体动物，以重建过去的干旱和水分来源。通过瞄准海洋和陆地碳酸盐共存的环境，研究人员可以了解碳酸盐材料可能带来的潜在季节性偏差以及水文循环的不同方面。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。

Dr. Julia Kelson has been granted an NSF EAR Postdoctoral fellowship to carry out research and educational activities at the University of Michigan, Ann Arbor. This project investigates the water cycle during climates that are characterized by atmospheres with high concentrations of greenhouse (heat-trapping) gases like carbon dioxide. As long as atmospheric concentrations of greenhouse gases continue to increase, we may observe more evaporation and more seasonally intense precipitation (rain/snow) in future climates. One way to understand such changes in the intensity of the hydrologic cycle is to explore the record of evaporation and precipitation during ancient high carbon dioxide climates, such as those of the early Cenozoic time period (65-30 million years ago). This project will develop a new tool to estimate the intensity of evaporation using ancient soil carbonates and mollusk shells. The chemical composition of these ancient carbonate materials contains information about the temperature of formation and the extent to which the rain/ground water from which they grew was affected by evaporation. Thus, this tool will allow for a simultaneous estimate of earth surface temperature and of aridity. The investigator will convey the importance of understanding ancient environmental change through outreach programs affiliated with the University of Michigan. One program is Earth Camp, which brings underrepresented high school students at no-cost to the university and to the field. Another program is Females Excelling More in Math and Engineering Sciences (FEMMES), which encourages girls to explore their potential in science. This project is leveraging two novel stable carbonate isotope measurements to improve our ability to reconstruct aridity and precipitation of ancient climates. This research consists of two components: 1) a modern calibration study, where the isotopic composition of modern soil carbonates and mollusk shells are measured, along with the isotopes of modern meteoric waters, to add to the growing understanding of how the isotopic composition of carbonates reflect their environment, and 2) an application to an ancient greenhouse climate, where these new proxies are applied to a Paleocene section in California that has both paleosol carbonates and mollusks in order to reconstruct past aridity and moisture sources. By targeting environments where marine and terrestrial carbonates are collocated, the investigator can understand the potential seasonal biases that the carbonate materials may impart as well as different aspects of the hydrologic 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.