Surface ocean marine dissolved organic matter (DOM) serves as an important reservoir of carbon (C), nitrogen (N), and phosphorus (P) in the global ocean, and is produced and consumed by both autotrophic and heterotrophic communities. While prior work has described distributions of dissolved organic carbon (DOC) and nitrogen (DON) concentrations, our understanding of DOC:DON:DOP stoichiometry in the global surface ocean has been limited by the availability of DOP concentration measurements. Here we estimate mean surface ocean bulk and labile DOC:DON:DOP stoichiometry in biogeochemically and geographically defined regions, using newly available marine DOM concentration databases. Global mean surface ocean bulk (C:N:P = 387:26:1) and labile (C:N:P = 179:20:1) DOM stoichiometries are higher than Redfield stoichiometry, with labile DOM stoichiometry similar to that of global mean surface ocean particulate organic matter (C:N:P = 160:21:1) reported in a recent compilation. DOM stoichiometry varies across ocean basins, ranging from 251:17:1 to 638:43:1 for bulk and 83:15:1 to 414:49:1 for labile DOM C:N:P, respectively. Surface ocean DOP exhibits larger relative changes than DOC and DON, driving surface ocean gradients in DOC:DON:DOP stoichiometry. Inferred autotrophic consumption of DOP helps explain intra- and inter-basin patterns of marine DOM C:N:P stoichiometry, with regional patterns of water column denitrification and iron supply influencing the biogeochemical conditions favoring DOP use as an organic nutrient. Specifically, surface ocean marine DOM exhibits increasingly P-depleted stoichiometries from east to west in the Pacific and from south to north in the Atlantic consistent with patterns of increasing P stress and alleviated iron stress, respectively.

Dissolved organic nitrogen (DON) and phosphorus (DOP) are potential nutrient sources to sustain productivity in the oligotrophic ocean where inorganic nutrient concentrations are low. Variations in the carbon(C):nitrogen(N):phosphorus(P) stoichiometry of surface ocean dissolved organic matter (DOM) can trace patterns of DON and DOP production and consumption, however, concurrent dissolved organic carbon (DOC), DON, and DOP concentration observations are limited. Using new global ocean DOM concentration datasets, we develop inverse DOC and DON models to obtain global ocean DOC and DON concentration fields and associated biogeochemical fluxes. Including autotrophic DON uptake improves the model fit to observations. Combining our modeled DOC and DON concentration fields with a global ocean DOP concentration field from our previous inverse DOP model, we obtain a modeled global ocean DOM stoichiometry field. We further evaluate the lateral transport of semi-labile DON (SLDON) and semi-labile DOP (SLDOP) to the oligotrophic low latitudes (15˚to 40˚) and identify the equatorial Pacific and Atlantic as important sources of SLDON and SLDOP. We also quantify the preferential loss of DON and DOP relative to DOC from the surface to 500 m, which, with physical circulation, may retain nutrients in the gyres, further enhancing productivity. Our findings highlight two modes by which DON and DOP serve as organic nutrient sources to sustain productivity in the oligotrophic low latitudes, with lateral transport more important and capable of supporting ~6 to 15% of export production in these regions.