Atlantic a Source of Nitrogen to the Global Ocean

The continental shelves receive N from the open ocean (820 x 10 molyear ), from estuaries (250 x 10 mol year ), from major rivers (350 x 10 mol year ) and from atmospheric deposition (130 x 10 mol year ). Some is lost to the sediments (120 x 10 mol year ) and fish catch (32 x 10 mol year ), but the majority is removed from the system via sedimentary denitrification (1400 x 10 mol year ). Nitrogen introduced to the shelves from the open ocean appears to contribute the most to shelf denitrification (Seitzinger and Gibhn, 1996). 

On balance, the shelves are not a net source of N to the open ocean. Instead, the North Atlantic has major exchanges with the Arctic Ocean and with the South Atlantic. Ganachaud and Wunsch (2002) estimate southerly nitrate fluxes of 2200 (+/- 3800) and 6600 (+/- 4700) x 10 mol N year- at 7.5°N and 4.5°S, respectively. We take their mid point value of 4400 (+/— 4000) X 10 mol N year as the net transport of nitrate from the North Atlantic to the South Atlantic. A significant uncertainty lies in the net meridional transport of DON in the basinwide N transport budgets in the Atlantic. Rintoul and Wunsch (1991) speculated that the imbalance they quantified in the poleward nitrate flux across subtropical sections may be compensated by unobserved fluxes of organic nitrogen. DON measurements are stiU too sparse and too imprecise to test this hypothesis. 

The nitrate flux from the Arctic to the Atlantic was estimated by Galloway et al. (1996) as 1500 x 10 mol year, with most of the nitrate due to Pacific water 

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