Fig. 3. Major production and loss pathways for marine RDOC.

These include (i) photochemical degradation via sunlight (hν) in seawater to form CO₂ and other oxidized products, some of which are biologically labile or chemically reactive; (ii) biological, chemical, and physical formation and loss processes associated with living and nonliving POC; (iii) degradation during transit through hydrothermal vent systems; and (iv) the association of RDOC with rising bubble plumes and subsequent emission into the atmosphere as a component of PMA. The RDOC associated with PMA may then be photochemically degraded (see Discussion) and/or (v) transported inland or (vi) returned to the sea.