EAR-PF: Light- and Iron-Mediated Oxidation Mechanisms of Organic Matter

Joe-Wong, Claresta Michelle, Stanford CA

Investigators

Abstract

Dr. Claresta Joe-Wong has been awarded a postdoctoral fellowship to work at Lawrence Berkeley National Laboratory on understanding carbon cycling between the atmosphere and inland waters, which is of increasing importance due to global climate change. Inland waters are a crucial component of the global carbon cycle because they transport organic carbon from soils to oceans; bury it in sediments; and release it as carbon dioxide, yet the natural processes that oxidize organic carbon to carbon dioxide in inland waters are not well understood. This project will characterize one of the most important yet poorly constrained of these processes, the oxidation of dissolved organic carbon in sunlight when iron is present. This research, which links these mechanisms at the molecular level to broad climatic changes, will be used to inform undergraduate lesson plans that link chemical principles to earth sciences processes. Undergraduates will be engaged in summer research internships and expose them to innovative techniques in the earth sciences. The postdoctoral fellow will benefit from broadening her research perspective and methods as well as the mentoring experience gained for her future career. Complexation with iron can enhance the reactivity of organic carbon with light, resulting in the release of carbon dioxide. However, the plethora of oxidation pathways involving short-lived radical intermediates makes it difficult to predict the effects of iron. The proposed work will experimentally characterize the reaction mechanisms and reactive intermediates of iron-mediated photo-oxidation using ultrafast spectroscopy with sub-picosecond resolution. Spectroscopic characterization of the photoreactivity of model carboxylates will be paired with laboratory experiments determining the kinetics and products of iron-mediated photolysis of dissolved organic carbon collected from the East River watershed in Colorado and Arctic Long-Term Ecological Research site in Alaska. Ultimately, integrating a mechanistic understanding of the photo-oxidation of dissolved organic carbon with large-scale models of carbon fluxes may promote a more comprehensive conceptual framework of carbon dynamics. 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.