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| Titel |
Measurements of nitrite production in and around the primary nitrite maximum in the central California Current |
| VerfasserIn |
A. E. Santoro, C. M. Sakamoto, J. M. Smith, J. N. Plant, A. L. Gehman, A. Z. Worden, K. S. Johnson, C. A. Francis, K. L. Casciotti |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-19), S.7395-7410 |
| Datensatznummer |
250085422
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| Publikation (Nr.) |
 copernicus.org/bg-10-7395-2013.pdf |
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| Zusammenfassung |
| Nitrite (NO2−) is a substrate for both oxidative and reductive
microbial metabolism. NO2− accumulates at the base of the euphotic
zone in oxygenated, stratified open-ocean water columns, forming a feature
known as the primary nitrite maximum (PNM). Potential pathways of
NO2− production include the oxidation of ammonia (NH3) by
ammonia-oxidizing bacteria and archaea as well as assimilatory nitrate
(NO3−) reduction by phytoplankton and heterotrophic bacteria.
Measurements of NH3 oxidation and NO3− reduction to NO2−
were conducted at two stations in the central California Current in the
eastern North Pacific to determine the relative contributions of these
processes to NO2− production in the PNM. Sensitive
(< 10 nmol L−1), precise measurements of [NH4+] and
[NO2−] indicated a persistent NH4+ maximum overlying the PNM
at every station, with concentrations as high as
1.5 μmol L−1. Within and just below the PNM, NH3
oxidation was the dominant NO2− producing process, with rates of
NH3 oxidation to NO2− of up to 31 nmol L−1 d−1,
coinciding with high abundances of ammonia-oxidizing archaea. Though little
NO2− production from NO3− was detected, potentially
nitrate-reducing phytoplankton (photosynthetic picoeukaryotes,
Synechococcus, and Prochlorococcus) were present at the
depth of the PNM. Rates of NO2− production from NO3− were
highest within the upper mixed layer (4.6 nmol L−1 d−1) but were
either below detection limits or 10 times lower than NH3 oxidation rates
around the PNM. One-dimensional modeling of water column NO2−
production agreed with production determined from 15N bottle incubations
within the PNM, but a modeled net biological sink for NO2− just below
the PNM was not captured in the incubations. Residence time estimates of
NO2− within the PNM ranged from 18 to 470 days at the mesotrophic station
and was 40 days at the oligotrophic station. Our results suggest the PNM is a
dynamic, rather than relict, feature with a source term dominated by ammonia
oxidation. |
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