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

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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.