The University of Southampton
University of Southampton Institutional Repository

Origin and fate of the secondary nitrite maximum in the Arabian Sea

Origin and fate of the secondary nitrite maximum in the Arabian Sea
Origin and fate of the secondary nitrite maximum in the Arabian Sea
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.
1726-4170
1565-1577
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
Jensen, M.M.
fe8d479f-35bb-4e1e-adf3-f2489838de3b
Kock, A.
7548b650-3832-4816-9fa6-3d2eb9570e37
Lettmann, K.A.
7b2a9cdc-e689-415f-a767-32213af4575d
Plancherel, Y.
1b986f9f-1c69-4a47-989d-016009eab584
Lavik, G.
50c5fdc6-5137-4d83-b3b9-ffe522b905d1
Bange, H.W.
7bcd0b9b-19e8-4462-a79d-9978c88aabb4
Kuypers, M.M.M.
8606877b-5eb8-4627-8d46-8e225b320dd9
Lam, Phyllis
996aef80-a15d-4827-aed8-1b97b378f6ad
Jensen, M.M.
fe8d479f-35bb-4e1e-adf3-f2489838de3b
Kock, A.
7548b650-3832-4816-9fa6-3d2eb9570e37
Lettmann, K.A.
7b2a9cdc-e689-415f-a767-32213af4575d
Plancherel, Y.
1b986f9f-1c69-4a47-989d-016009eab584
Lavik, G.
50c5fdc6-5137-4d83-b3b9-ffe522b905d1
Bange, H.W.
7bcd0b9b-19e8-4462-a79d-9978c88aabb4
Kuypers, M.M.M.
8606877b-5eb8-4627-8d46-8e225b320dd9

Lam, Phyllis, Jensen, M.M., Kock, A., Lettmann, K.A., Plancherel, Y., Lavik, G., Bange, H.W. and Kuypers, M.M.M. (2011) Origin and fate of the secondary nitrite maximum in the Arabian Sea. Biogeosciences, 8 (6), 1565-1577. (doi:10.5194/bg-8-1565-2011).

Record type: Article

Abstract

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.

Full text not available from this repository.

More information

Published date: 2011
Organisations: Ocean Biochemistry & Ecosystems

Identifiers

Local EPrints ID: 349914
URI: https://eprints.soton.ac.uk/id/eprint/349914
ISSN: 1726-4170
PURE UUID: 1d78f48e-fbd7-4156-b24c-74817e9c17be
ORCID for Phyllis Lam: ORCID iD orcid.org/0000-0003-2067-171X

Catalogue record

Date deposited: 13 Mar 2013 13:43
Last modified: 22 Oct 2019 00:35

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×