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| Titel |
Origin and fate of the secondary nitrite maximum in the Arabian Sea |
| VerfasserIn |
P. Lam, M. M. Jensen, A. Kock, K. A. Lettmann, Y. Plancherel, G. Lavik, H. W. Bange, M. M. M. Kuypers |
| 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 ; 8, no. 6 ; Nr. 8, no. 6 (2011-06-20), S.1565-1577 |
| Datensatznummer |
250005957
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| Publikation (Nr.) |
 copernicus.org/bg-8-1565-2011.pdf |
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| Zusammenfassung |
| The Arabian Sea harbours one of the three major oxygen minimum zones (OMZs)
in the world's oceans, and it alone is estimated to account for ~10–20 % of global oceanic nitrogen (N) loss. While actual rate
measurements have been few, the consistently high accumulation of nitrite
(NO2−) coinciding with suboxic conditions in the
central-northeastern part of the Arabian Sea has led to the general belief
that this is the region where active N-loss takes place. Most subsequent
field studies on N-loss have thus been drawn almost exclusively to the
central-NE. However, a recent study measured only low to undetectable N-loss
activities in this region, compared to orders of magnitude higher rates
measured towards the Omani Shelf where little NO2−
accumulated (Jensen et al., 2011). In this paper, we further
explore this discrepancy by comparing the NO2−-producing
and consuming processes, and examining the relationship between the overall
NO2− balance and active N-loss in the Arabian Sea. Based on
a combination of 15N-incubation experiments, functional gene expression
analyses, nutrient profiling and flux modeling, our results showed that
NO2− accumulated in the central-NE Arabian Sea due to a net
production via primarily active nitrate (NO3−) reduction and
to a certain extent ammonia oxidation. Meanwhile, NO2−
consumption via anammox, denitrification and dissimilatory nitrate/nitrite
reduction to ammonium (NH4+) were hardly detectable in this
region, though some loss to NO2− oxidation was predicted
from modeled NO3− changes. No significant correlation was
found between NO2− and N-loss rates (p>0.05). This
discrepancy between NO2− accumulation and lack of active
N-loss in the central-NE Arabian Sea is best explained by the deficiency of labile
organic matter that is directly needed for further NO2−
reduction to N2O, N2 and NH4+, and indirectly for the
remineralized NH4+ required by anammox. Altogether, our data do
not support the long-held view that NO2− accumulation is a
direct activity indicator of N-loss in the Arabian Sea or other OMZs.
Instead, NO2− accumulation more likely corresponds to
long-term integrated N-loss that has passed the prime of high and/or
consistent in situ activities. |
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