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Low contribution of N2 fixation to new production and excess nitrogen in the subtropical northeast Atlantic margin

AuthorsBenavides, Mar; Arístegui, Javier; Agawin, Nona S. R. ; Álvarez-Salgado, Xosé Antón ; Álvarez, Marta ; Troupin, Charles
KeywordsNew production
Regenerated production
Dissolved organic nitrogen release
Issue Date2013
CitationDeep Sea Research - Part I - Oceanographic Research Papers 81: 36-48 (2013)
AbstractWe used 15N-labeled substrates to measure dinitrogen (N2) fixation, nitrate (NO3−) and ammonium (NH4+) uptake, regeneration and associated dissolved organic nitrogen (DON) release in a coastal upwelling system (Cape Ghir, ∼31°N) and an open ocean grid (bounded between 25°–42°N and 20°W) in the Canary Current region during the summer of 2009. New production (Pnew=NO3− uptake+N2 fixation+DON released from NO3− uptake−NO3− regeneration) was higher in the upwelling than in the open ocean zone (0.126 and 0.014 µmol N L−1 h−1, respectively), while regenerated production (Preg=NH4+ uptake+DON released from NH4+ uptake+NH4+ regeneration) was similar in both zones (0.157 and 0.133 µmol N L−1 h−1, respectively). The resulting f-ratio (Pnew/Pnew+Preg) for the open ocean and upwelling zones was 0.08 and 0.48, respectively. The availability of nitrogen in excess of that expected from Redfield stoichiometry is generally attributed to N2 fixation. A previous study indicated that our open ocean grid zone had an excess nitrogen production rate of 40±22×1010 mol N yr−1. We revisited this budget including new dissolved organic matter and NO3− fluxes through the Strait of Gibraltar and estimated a revised nitrogen excess rate of 22±19×1010 mol N yr−1. The average volumetric rate of N2 fixation for this zone was only 1.3×10−3 nmol N L−1 d−1, indicating that its influence in Pnew and nitrogen excess production in this part of the Atlantic is negligible.
Description13 páginas, 5 figuras, 5 tablas
Publisher version (URL)http://dx.doi.org/10.1016/j.dsr.2013.07.004
Appears in Collections:(IIM) Artículos
(IMEDEA) Artículos
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