An understanding of the cycling of carbon and nitrogen in the surface ocean is necessary for many reasons, including understanding the impacts of marine and other environmental changes in a changing climate. Much of the research focus has been on inorganic forms of carbon and nitrogen and, in particular, little is known about the cycling of dissolved organic nitrogen (DON) compounds in the surface ocean and their impact. Researchers at the University of Texas at Austin will investigate peptides and proteins, one class or organic nitrogen compounds released from marine biota. These compounds can be taken up and incorporated if they have sufficiently small molecular weight and/or recycled back to inorganic nitrogen by bacteria, potentially supporting primary production. Conversion, primarily by extracellular enzymatic hydrolysis, produces small peptides or free amino acids that can be assimilated by microbes. The proposed research will investigate the mechanisms of peptide hydrolysis, their importance in the overall breakdown and/or preservation of DON in ocean waters, and the role of chemical structure in influencing the reaction pathways. The study will use novel and innovative techniques which are a substantial advancement over currently used approaches, to examine these processes. These approaches include the use of isotopically labeled compounds as well as specific compounds (peptides and related compounds) manufactured in the laboratory. The study should provide significant advancements in our understanding of DON dynamics in the marine nitrogen cycle. The project will involve students at the graduate, undergraduate and high school level and will have a significant outreach component. Interactions will include summer undergraduate programs, public seminars and related activities and Science and the Sea, a syndicated radio program.