Premium
Downward transport and fate of organic matter in the ocean: Simulations with a general circulation model
Author(s) -
Najjar Raymond G.,
Sarmiento Jorge L.,
Toggweiler J. R.
Publication year - 1992
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/91gb02718
Subject(s) - upwelling , new production , oceanography , nutrient , hydrography , environmental science , flux (metallurgy) , photic zone , organic matter , sediment trap , nutrient cycle , colored dissolved organic matter , thermocline , redfield ratio , biological pump , geology , chemistry , phytoplankton , water column , organic chemistry
A phosphorus‐based model of nutrient cycling has been developed and used in conjunction with a general circulation model to evaluate the roles of the dissolved and sinking particulate phases in the downward transport of organic matter in the ocean. If sinking particles dominate the downward transport and remineralize in accord with observations made primarily with sediment traps, we find in equatorial upwelling regions that particle fluxes and thermocline nutrient concentrations are higher than observed. These enhanced fluxes and concentrations are a result of what we term “nutrient trapping,” a positive feedback whereby high upwelling produces high new production that results in remineralization and enhanced nutrient concentrations in the upwelling water, which further increases new production. Nutrient trapping in shallow upwelling zones can be eliminated by increasing the particle flux length scale, which suggests that if sinking particles dominate the downward transport of organic matter then the flux length scale is longer than observed. Even with a longer particle flux length scale, we find that nutrients are trapped in some deep convective regions of the southern ocean, where new production is predicted to be much higher than the observed primary production. In simulations where the downward transport of organic matter takes place primarily in a dissolved phase, nutrient trapping is completely eliminated, in both upwelling and convective regions. The models with dissolved organic matter also agree fairly well with nutrient transports in the north Atlantic Ocean calculated from observed nutrient and hydrographic data (Rintoul and Wunsch, 1991). Our results therefore support the dissolved organic nitrogen and carbon measurements made with the high‐temperature combustion technique of Suzuki et al. (1985) and Sugimura and Suzuki (1988) and suggest that there exists an as‐yet undiscovered pool of dissolved organic phosphorus in the ocean. We also use the various models to make an estimate of global new production of 2.9 to 3.6 mol C/m 2 /yr (12 to 15 Gt C/yr).