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Potential use of the N 2 /Ar ratio as a constraint on the oceanic fixed nitrogen loss
Author(s) -
Shigemitsu M.,
Gruber N.,
Oka A.,
Yamanaka Y.
Publication year - 2016
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 - 10.1002/2015gb005297
Subject(s) - denitrification , water column , benthic zone , biogeochemical cycle , nitrogen , environmental science , nitrogen cycle , oceanography , tracer , environmental chemistry , soil science , chemistry , geology , physics , organic chemistry , nuclear physics
Using a global ocean biogeochemical model, we investigate the suitability of the N 2 /Ar supersaturation ratio (ΔN 2 /Ar) as a tracer of marine nitrogen fixation and denitrification, i.e., the main biological processes that add or remove fixed nitrogen to or from the ocean. In a series of factorial simulations, we demonstrate that, in regions away from the oxygen minimum zones (OMZs), the ΔN 2 /Ar characteristics are mostly determined by benthic denitrification occurring in the deep ocean with minor contributions from benthic and water column denitrification at shallower depths. In the OMZs, the subsurface maxima of ΔN 2 /Ar are mainly determined by water column denitrification. In contrast, nitrogen fixation has little impact on ΔN 2 /Ar owing to the rapid loss of the N 2 supersaturation signal through air‐sea exchange. We thus conclude that ΔN 2 /Ar can act as a powerful constraint on water column and benthic denitrification occurring in intermediate to deep waters, but it cannot be used to estimate nitrogen fixation. A comparison between the currently very limited observations of the ΔN 2 /Ar with our model results shows an acceptable level of agreement, suggesting that the model's prescribed rates and distributions of benthic and water column denitrification (i.e., 140 and 52 Tg N yr −1 , respectively) are reasonable and confirm the results derived from other constraints.