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Fixed nitrogen loss from the eastern tropical North Pacific and Arabian Sea oxygen deficient zones determined from measurements of N 2 :Ar
Author(s) -
Chang Bonnie X.,
Devol Allan H.,
Emerson Steven R.
Publication year - 2012
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 - 10.1029/2011gb004207
Subject(s) - denitrification , nitrogen , oxygen , nitrate , oxygen minimum zone , chemistry , environmental science , organic chemistry
Previous work estimating the N 2 excess above background due to denitrification has suggested that nitrate deficit‐type methods may be an underestimate of fixed nitrogen (N) loss in the major oxygen deficient zones of the ocean. The N 2 excess approach has the advantage over nitrate deficit‐type methods in that it does not depend on stoichiometric assumptions of fixed N to phosphate or oxygen utilization and avoids any uncertainly regarding the pathway of N loss. Measurements of N 2 :Ar from two stations within the eastern tropical North Pacific and from one station within the Arabian Sea oxygen deficient zones were used to determine the N 2 excess due to denitrification. In both of the regions, the N 2 excess was comparable in shape and magnitude to the concurrent fixed nitrogen deficit. In the eastern tropical North Pacific oxygen deficient zone, the N 2 excess was near zero at the surface and rose to maxima of 13.7 ± 1.8 and 10.8 ± 1.9 μ M N, compared to maximum fixed N deficits of 13.5 ± 1.5 and 12.3 ± 1.5 μ M N, respectively. In the Arabian Sea oxygen deficient zone, the maximum N 2 excess was 11.1 ± 1.5 μ M N, compared to a maximum deficit of 12.5 ± 1.0 μ M N. These results suggests that previous estimates of fixed N loss based on fixed N deficit calculations in these regions are likely reasonable, given the same considerations of volume and residence time of the water of the oxygen deficient zone.