In marine systems DOC originates from either autochthonous or allochthonous sources. Autochthonous DOC is produced within the system, primarily by plankton organisms  and in coastal waters additionally by benthic microalgae, benthic fluxes, and macrophytes, whereas allochthonous DOC is mainly of terrestrial origin supplemented by groundwater and atmospheric inputs. In addition to soil derived humic substances, terrestrial DOC also includes material leached from plants exported during rain events, emissions of plant materials to the atmosphere and deposition in aquatic environments (e.g., volatile organic carbon and pollens), and also thousands of synthetic human-made organic chemicals that can be measured in the ocean at trace concentrations.
Dissolved organic carbon (DOC) represents one of the Earth's major carbon pools. It contains a similar amount of carbon as the atmosphere and exceeds the amount of carbon bound in marine biomass by more than two-hundred times. DOC is mainly produced in the near-surface layers during primary production and zooplankton grazing processes. Other sources of marine DOC are dissolution from particles, terrestrial and hydrothermal vent input, and microbial production. Prokaryotes (bacteria and archaea) contribute to the DOC pool via release of capsular material, exopolymers, and hydrolytic enzymes, as well as via mortality (e.g. viral shunt). Prokaryotes are also the main decomposers of DOC, although for some of the most recalcitrant forms of DOC very slow abiotic degradation in hydrothermal systems or possibly sorption to sinking particles may be the main removal mechanism. Mechanistic knowledge about DOC-microbe-interactions is crucial to understand the cycling and distribution of this active carbon reservoir.