Dissolved Organic Carbon (DOC)

Dissolved organic carbon (DOC) is the operationally defined fraction of organic carbon that passes a filter, commonly 0.2 to 0.7 micrometers, separating it from particulate organic carbon. At about 660 petagrams it is one of the largest reduced-carbon reservoirs in the ocean, comparable to atmospheric CO2. Surface DOC near 60 to 80 micromoles per liter falls to roughly 34 to 40 micromoles in the deep sea, where the residual is refractory with a radiocarbon age of thousands of years. Phytoplankton exudation and grazing release labile DOC that the microbial loop consumes, routing carbon back to CO2.