Nutrient supply to the surface waters of the North Atlantic - a model study

Oschlies, A. (2002) Nutrient supply to the surface waters of the North Atlantic - a model study. Journal of Geophysical Research, 107, 3046. (doi:10.1029/2000JC000275).

Abstract

An eddy-permitting coupled ecosystem-circulation model with accurate descriptions of advection and turbulent mixing is used to estimate the nitrate supply to the euphotic zone in the North and equatorial Atlantic Ocean. The simulated annual mean input of nitrate into the euphotic zone is separated into different supply routes, namely, turbulent vertical mixing, vertical advection, and horizontal transport. Vertical mixing is found to be the dominant supply mechanism in the subpolar North Atlantic, while horizontal advection provides most of the simulated nitrate input into the subtropical gyre. Contributions by vertical advection are largest in the equatorial upwelling region and in the subpolar gyre. A comparison with observational estimates of nitrate flux into euphotic zone of the subtropical gyre reveals that the model can simultaneously fit the estimates by Lewis et al. [1986] and Jenkins [1988] that were previously thought to be contradictory. The simulated nitrate supply is, on the other hand, not consistent with estimates of export production based on oxygen consumption [ Jenkins, 1982 ]. The model results are used to investigate to what extent the advective input of organic matter could possibly explain a local imbalance between new and export production. It turns out that the simulated advective input of organic matter alone, which in the model provides nitrogen at a rate similar to that arising from nitrate supply, is not sufficient to explain observed oxygen consumption rates.

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