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Dissolved organic nitrogen production and export by meridional overturning in the eastern subpolar North Atlantic
Dissolved organic matter (DOM) is produced in the surface and exported towards the deep ocean, adding ∼2 PgC yr−1 to the global carbon export. Due to its central role in the Meridional Overturning Circulation (MOC), the eastern subpolar North Atlantic (eSPNA) contributes largely to this export. Here we quantify the transport and budget of dissolved organic nitrogen (DON) in the eSPNA, in a box delimited by the OVIDE 2002 section and the Greenland‐Iceland‐Scotland sills. The MOC exports >15.9 TgN yr−1 of DON downwards and, contrary to the extended view that these are materials of subtropical origin, up to 33% of the vertical flux derives from a net local DON production of 7.1 ± 2.6 TgN yr−1. The low C:N molar ratio of DOM production (7.4 ± 4.1) and the relatively short‐transit times in the eSPNA (3 ± 1 yr) suggest that local biogeochemical transformations result in the injection of fresh bioavailable DOM to the deep ocean.
Keyword(s)
dissolved organic matter, nitrogen cycle, meridional overturning circulation, subpolar North Atlantic, metabolic balance