Oligotrophic Ocean New Production Supported by Lateral Transport of Dissolved Organic Nutrients

Abstract

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 data sets, 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 ∼6–15% of export production in these regions.