Congratulations to Rebekah Stein who defended her dissertation on Friday, November 6, 2020
Advisor: Nathan Sheldon
During modern times of unprecedented climate change, understanding the role that the terrestrial biosphere plays in the carbon and water cycle is imperative. Plants and soils are excellent records for climate because of the direct interaction between the terrestrial biosphere and the atmosphere and their preservation potential. Organic carbon isotope records in plants and soils have been linked to several environmental, evolutionary, and edaphic drivers, in addition to being used to measure ecosystem stress. The period of Industrialization provides a natural experiment with measurable, uncontrolled climate, ideal for investigating the relationship between climate change (particularly related to the carbon and water cycles) and C isotope values. This dissertation includes several high-resolution spatiotemporal studies of a number of plant species over Industrialization; in Chapter II, leaf carbon isotope values from a single Great Lakes region species are compared to several atmospheric carbon and water variables in addition to a number of other climate drivers over the span of 200 years. Chapter III expands on results from previous experiments, tackling the controversial relationship between the carbon dioxide of the atmosphere and plant carbon isotope geochemistry with eight focal species from across the Northern Hemisphere. In Chapter IV, findings from previous chapters are re-examined from the context of aboveground carbon integrator: soils. This work explores the relationship between carbon isotope values found in modern soil organic matter compared to climate. This work also tests the relationship between soil carbon isotopes and precipitation in ancient soils (paleosols). Chapter V integrates the results and conclusions from early dissertation chapters with pre-established geochemical and physiognomic proxies, for a comprehensive analysis of early Eocene hothouse sediments. Though climate variables are not as well-constrained as the unique period of Industrialization, depositional basins from the Eocene are well-studied and contain opportunities for multi-proxy-based environmental reconstruction. In summary, this dissertation contains case studies incorporating the roles of soils and plants in the carbon and water cycle in modern, historical and deep time.