Colored dissolved organic matter (CDOM) is distributed throughout the world ocean and may be a major determinant of the optical properties of oligotrophic ocean waters. It may also play a major role in biogeochemically significant photochemical reactions that we are only beginning to recognize -- let alone understand. In this study, three young scientists at the Bermuda Biological Laboratory for Research will test several hypotheses regarding microbially-mediated production of CDOM and its photolytic decomposition. Four sets of experiments will be undertaken in Sargasso Sea environments near the Bermuda Atlantic Time-Series site to determine (1) the microbial production of CDOM as a function of the quality of DOM, (2) the photophysical properties of CDOM as a function of origin, (3) alternate sources of CDOM (for example, zooplankton as opposed to phytoplankton and bacterioplankton), and (4) changes in the bioavailability of CDOM to microbes after bleaching. The team expects to produce a quantitative description of the factors controlling CDOM distribution in the open ocean gyres far from land.