Award: OCE-1233373

Microorganisms play a dominant role in the ocean carbon cycle through carbon fixation (photosynthesis) and mineralization (respiration). The balance between these two biological processes influences the concentration of carbon dioxide in the atmosphere and our climate. Bacterial respiration is known to be responsible for the mineralization of about half of all the carbon fixed by photosynthesis every year. Our research investigated the composition and fate of bacterial metabolites that escape mineralization and persist in the ocean. Very little is known about this recently recognized process, which is important because this process can sequester carbon in the ocean and effectively remove carbon dioxide from the atmosphere. Our research used two approaches to investigate the significance of bacterial metabolites in the ocean carbon cycle. The first approach involved growing marine bacteria in the laboratory and harvesting the dissolved metabolites released into the seawater culture. State-of-the-art chemical analyses were used to characterize the composition and structure of the bacterial metabolites. The second approach involved collecting seawater samples form various locations in the ocean and isolating the dissolved molecules to examine their composition and structure using the same state-of-the-art analyses. The age of the dissolved organic molecules collected from the ocean was estimated from radiocarbon analyses and ranged from hundreds to thousands of years, indicating they can persist in the ocean for millennia. Comparison of the bacterial metabolites from the laboratory cultures with the dissolved molecules from the ocean demonstrated striking similarities in chemical composition and structure. This observation is of great significance because it demonstrates that the carbon sequestered in the deep ocean is of biological origin and can be rapidly synthesized by bacteria. Previous studies suggested the sequestered carbon was predominantly the product of abiotic processes, such as thermal and photochemical alterations. Our research and findings also generate many new questions about the controls on the ocean carbon cycle. Graduate and undergraduate students participated in this project along with a postdoctoral associate. All participants engaged in presenting the results of the research at national and regional meetings and conferences. This project provided critical and invaluable experience for these young and aspiring scientists. Last Modified: 09/08/2016 Submitted by: Ronald Benner