The organic carbon cycle operates on multiple time scales with a only small fraction of the global reservoir actively exchanged. For the marine system, the sources are principally recently synthesized material from autotrophic production which annually contribute 44–50 Pg/year of new organic carbon. This is supplemented by terrestrial carbon arriving from rivers, erosion and the atmosphere which contribute to the complex mixture present on oceanic waters. The focus of this review is to highlight the major sources or organic carbon and describe how the interaction of biological, chemical and physical processes provides an efficient mechanism for its eventual recycling.