Rivers and nitrate control DOC distribution in the upper Atlantic Ocean

By virtue of its global inventory, oceanic dissolved organic carbon (DOC) is an important intermediate in the global carbon cycle. Small changes in that inventory will have important impacts on the carbon cycle and on climate. DOC is mostly produced by primary production, in turn supported by nutrients that reach the euphotic zone. The newly produced material primarily supports heterotrophic microbes, but not all DOC is consumed; a fraction accumulates in the upper ocean until eventually being exported to depth. Here we seek to understand the controls on the distribution of DOC in the surface ocean, looking to the net DOC production terms. DOC in the surface ocean is not homogeneously distributed, with higher concentrations found in the tropics than at high latitudes (where unaffected by rivers). We have decomposed the main physical processes triggering net DOC production in the surface layer of the Atlantic Ocean: winter vertical mixing at high latitudes, and upwelling at low latitudes. A third control on the distribution is the input of terrigenous DOC by rivers. Using climatological nitrate and satellite-sensed salinity data, we reproduce reasonably well the distribution of DOC in the upper Atlantic, showing that the main controls of DOC are nitrate consumption (in support of net community production) and terrestrial inputs.