Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru
Depth profiles of nitrous oxide (N<sub>2</sub>O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/2013, covering both the coastal shelf region and the adjacent open ocean. N<sub>2</sub>O profiles displayed a strong...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-02-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/827/2016/bg-13-827-2016.pdf |
| _version_ | 1818961172913717248 |
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| author | A. Kock D. L. Arévalo-Martínez C. R. Löscher H. W. Bange |
| author_facet | A. Kock D. L. Arévalo-Martínez C. R. Löscher H. W. Bange |
| author_sort | A. Kock |
| collection | DOAJ |
| description | Depth profiles of nitrous oxide (N<sub>2</sub>O) were measured during six cruises
to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and
2012/2013, covering both the coastal shelf region and the adjacent open
ocean. N<sub>2</sub>O profiles displayed a strong sensitivity towards oxygen
concentrations. Open ocean profiles with distances to the shelf break larger
than the first baroclinic Rossby radius of deformation showed a transition
from a broad maximum close to the Equator to a double-peak structure south
of 5° S where the oxygen minimum was more pronounced. Maximum
N<sub>2</sub>O concentrations in the open ocean were about 80 nM. A linear
relationship between ΔN<sub>2</sub>O and apparent oxygen utilization (AOU)
could be found for measurements within the upper oxycline, with a slope
similar to studies in other oceanic regions. In contrast, N<sub>2</sub>O profiles
close to the shelf revealed a much higher variability, and N<sub>2</sub>O
concentrations higher than 100 nM were often observed. The highest N<sub>2</sub>O
concentration measured at the shelf was ∼ 850 nM. Due to the
extremely sharp oxygen gradients at the shelf, N<sub>2</sub>O maxima occurred in
very shallow water depths of less than 50 m. In the coastal area, a linear
relationship between ΔN<sub>2</sub>O and AOU could not be observed as
extremely high ΔN<sub>2</sub>O values were scattered over the full range
of oxygen concentrations. The data points that showed the strongest
deviation from a linear ΔN<sub>2</sub>O ∕ AOU relationship also showed
signals of intense nitrogen loss. These results indicate that the coastal
upwelling at the Peruvian coast and the subsequent strong remineralization
in the water column causes conditions that lead to extreme N<sub>2</sub>O
accumulation, most likely due to the interplay of intense mixing and high
rates of remineralization which lead to a rapid switching of the OMZ waters
between anoxic and oxic conditions. This, in turn, could trigger incomplete
denitrification or pulses of increased nitrification with extreme N<sub>2</sub>O
production. |
| first_indexed | 2024-12-20T12:09:13Z |
| format | Article |
| id | doaj.art-2d0b6afa79634b7397361828284a592d |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-20T12:09:13Z |
| publishDate | 2016-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-2d0b6afa79634b7397361828284a592d2022-12-21T19:41:17ZengCopernicus PublicationsBiogeosciences1726-41701726-41892016-02-0113382784010.5194/bg-13-827-2016Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off PeruA. Kock0D. L. Arévalo-Martínez1C. R. Löscher2H. W. Bange3GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, GermanyGEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, GermanyGEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, GermanyGEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, GermanyDepth profiles of nitrous oxide (N<sub>2</sub>O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/2013, covering both the coastal shelf region and the adjacent open ocean. N<sub>2</sub>O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles with distances to the shelf break larger than the first baroclinic Rossby radius of deformation showed a transition from a broad maximum close to the Equator to a double-peak structure south of 5° S where the oxygen minimum was more pronounced. Maximum N<sub>2</sub>O concentrations in the open ocean were about 80 nM. A linear relationship between ΔN<sub>2</sub>O and apparent oxygen utilization (AOU) could be found for measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. In contrast, N<sub>2</sub>O profiles close to the shelf revealed a much higher variability, and N<sub>2</sub>O concentrations higher than 100 nM were often observed. The highest N<sub>2</sub>O concentration measured at the shelf was ∼ 850 nM. Due to the extremely sharp oxygen gradients at the shelf, N<sub>2</sub>O maxima occurred in very shallow water depths of less than 50 m. In the coastal area, a linear relationship between ΔN<sub>2</sub>O and AOU could not be observed as extremely high ΔN<sub>2</sub>O values were scattered over the full range of oxygen concentrations. The data points that showed the strongest deviation from a linear ΔN<sub>2</sub>O ∕ AOU relationship also showed signals of intense nitrogen loss. These results indicate that the coastal upwelling at the Peruvian coast and the subsequent strong remineralization in the water column causes conditions that lead to extreme N<sub>2</sub>O accumulation, most likely due to the interplay of intense mixing and high rates of remineralization which lead to a rapid switching of the OMZ waters between anoxic and oxic conditions. This, in turn, could trigger incomplete denitrification or pulses of increased nitrification with extreme N<sub>2</sub>O production.http://www.biogeosciences.net/13/827/2016/bg-13-827-2016.pdf |
| spellingShingle | A. Kock D. L. Arévalo-Martínez C. R. Löscher H. W. Bange Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru Biogeosciences |
| title | Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru |
| title_full | Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru |
| title_fullStr | Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru |
| title_full_unstemmed | Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru |
| title_short | Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru |
| title_sort | extreme n sub 2 sub o accumulation in the coastal oxygen minimum zone off peru |
| url | http://www.biogeosciences.net/13/827/2016/bg-13-827-2016.pdf |
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