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 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.