The University of Southampton
University of Southampton Institutional Repository

Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system

Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system
Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system
Eastern boundary upwelling systems (EBUS) are regions of high primary production often associated with oxygen minimum zones (OMZs). They represent key regions for the oceanic nitrogen (N) cycle. By exporting organic matter (OM) and nutrients produced in the coastal region to the open ocean, EBUS can play an important role in sustaining primary production in subtropical gyres. However, losses of fixed inorganic N through denitrification and anammox processes take place in oxygen depleted environments such as EBUS, and can potentially mitigate the role of these regions as a source of N to the open ocean. EBUS can also represent a considerable source of nitrous oxide (N2O) to the atmosphere, affecting the atmospheric budget of N2O.

In this paper a 3-D coupled physical/biogeochemical model (ROMS/BioEBUS) is used to investigate the N budget in the Namibian upwelling system. The main processes linked to EBUS and associated OMZs are taken into account. The study focuses on the northern part of the Benguela upwelling system (BUS), especially the Walvis Bay area (between 22° S and 24° S) where the OMZ is well developed. Fluxes of N off the Walvis Bay area are estimated in order to understand and quantify (1) the total N offshore export from the upwelling area, representing a possible N source that sustains primary production in the South Atlantic subtropical gyre; (2) export production and subsequent losses of fixed N via denitrification and anammox under suboxic conditions (O2 < 25 mmol O2 m?3); and (3) the N2O emission to the atmosphere in the upwelling area.

In the mixed layer, the total N offshore export is estimated as 8.5 ± 3.9 × 1010 mol N yr?1 at 10° E off the Walvis Bay area, with a mesoscale contribution of 20%. Extrapolated to the whole BUS, the coastal N source for the subtropical gyre corresponds to 0.1 ± 0.04 mol N m?2 yr?1. This N flux represents a major source of N for the gyre compared with other N sources, and contributes 28% of the new primary production estimated for the South Atlantic subtropical gyre.

Export production (16.9 ± 1.3 × 1010 mol N yr?1) helps to maintain an OMZ off Namibia in which coupled nitrification, denitrification and anammox processes lead to losses of fixed N and N2O production. However, neither N losses (0.04 ± 0.025 × 1010 mol N yr?1) nor N2O emissions (0.03 ± 0.002 × 1010 mol N yr?1) significantly impact the main N exports of the Walvis Bay area.

The studied area does not significantly contribute to N2O emissions (0.5 to 2.7%) compared to the global coastal upwelling emissions. Locally produced N2O is mostly advected southward by the poleward undercurrent.
1726-4170
4117-4135
Gutknecht, E.
1742cd3b-a48a-4602-952b-ca8c8207789d
Dadou, I.
7bb564ca-e9a7-4b43-a809-ec25c69d4c75
Marchesiello, P.
6c809642-5d60-4d1b-912a-2234827a50c5
Cambon, G.
a2066749-6e7f-431b-b536-46c215f66b28
Le Vu, B.
7e6ffcd2-117d-4b0d-bd90-e4c0f0ebe683
Sudre, J.
8f950b51-3660-4da9-a76d-fc98f3359a0b
Garçon, V.
e8d06683-c40a-484a-9744-cd9fd8ed156b
Machu, E.
c6ec8b3d-ff72-41ee-8510-412261ee3b38
Rixen, T.
dc65e23d-a115-4dbd-8aa8-7b1d402d6c66
Kock, A.
7548b650-3832-4816-9fa6-3d2eb9570e37
Flohr, A.
1e293a22-bdba-408e-9608-fed8b65e4e79
Paulmier, A.
22dfe8e7-3872-40d7-859c-8923eda52441
Lavik, G.
50c5fdc6-5137-4d83-b3b9-ffe522b905d1
Gutknecht, E.
1742cd3b-a48a-4602-952b-ca8c8207789d
Dadou, I.
7bb564ca-e9a7-4b43-a809-ec25c69d4c75
Marchesiello, P.
6c809642-5d60-4d1b-912a-2234827a50c5
Cambon, G.
a2066749-6e7f-431b-b536-46c215f66b28
Le Vu, B.
7e6ffcd2-117d-4b0d-bd90-e4c0f0ebe683
Sudre, J.
8f950b51-3660-4da9-a76d-fc98f3359a0b
Garçon, V.
e8d06683-c40a-484a-9744-cd9fd8ed156b
Machu, E.
c6ec8b3d-ff72-41ee-8510-412261ee3b38
Rixen, T.
dc65e23d-a115-4dbd-8aa8-7b1d402d6c66
Kock, A.
7548b650-3832-4816-9fa6-3d2eb9570e37
Flohr, A.
1e293a22-bdba-408e-9608-fed8b65e4e79
Paulmier, A.
22dfe8e7-3872-40d7-859c-8923eda52441
Lavik, G.
50c5fdc6-5137-4d83-b3b9-ffe522b905d1

Gutknecht, E., Dadou, I., Marchesiello, P., Cambon, G., Le Vu, B., Sudre, J., Garçon, V., Machu, E., Rixen, T., Kock, A., Flohr, A., Paulmier, A. and Lavik, G. (2013) Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system. Biogeosciences, 10 (6), 4117-4135. (doi:10.5194/bg-10-4117-2013).

Record type: Article

Abstract

Eastern boundary upwelling systems (EBUS) are regions of high primary production often associated with oxygen minimum zones (OMZs). They represent key regions for the oceanic nitrogen (N) cycle. By exporting organic matter (OM) and nutrients produced in the coastal region to the open ocean, EBUS can play an important role in sustaining primary production in subtropical gyres. However, losses of fixed inorganic N through denitrification and anammox processes take place in oxygen depleted environments such as EBUS, and can potentially mitigate the role of these regions as a source of N to the open ocean. EBUS can also represent a considerable source of nitrous oxide (N2O) to the atmosphere, affecting the atmospheric budget of N2O.

In this paper a 3-D coupled physical/biogeochemical model (ROMS/BioEBUS) is used to investigate the N budget in the Namibian upwelling system. The main processes linked to EBUS and associated OMZs are taken into account. The study focuses on the northern part of the Benguela upwelling system (BUS), especially the Walvis Bay area (between 22° S and 24° S) where the OMZ is well developed. Fluxes of N off the Walvis Bay area are estimated in order to understand and quantify (1) the total N offshore export from the upwelling area, representing a possible N source that sustains primary production in the South Atlantic subtropical gyre; (2) export production and subsequent losses of fixed N via denitrification and anammox under suboxic conditions (O2 < 25 mmol O2 m?3); and (3) the N2O emission to the atmosphere in the upwelling area.

In the mixed layer, the total N offshore export is estimated as 8.5 ± 3.9 × 1010 mol N yr?1 at 10° E off the Walvis Bay area, with a mesoscale contribution of 20%. Extrapolated to the whole BUS, the coastal N source for the subtropical gyre corresponds to 0.1 ± 0.04 mol N m?2 yr?1. This N flux represents a major source of N for the gyre compared with other N sources, and contributes 28% of the new primary production estimated for the South Atlantic subtropical gyre.

Export production (16.9 ± 1.3 × 1010 mol N yr?1) helps to maintain an OMZ off Namibia in which coupled nitrification, denitrification and anammox processes lead to losses of fixed N and N2O production. However, neither N losses (0.04 ± 0.025 × 1010 mol N yr?1) nor N2O emissions (0.03 ± 0.002 × 1010 mol N yr?1) significantly impact the main N exports of the Walvis Bay area.

The studied area does not significantly contribute to N2O emissions (0.5 to 2.7%) compared to the global coastal upwelling emissions. Locally produced N2O is mostly advected southward by the poleward undercurrent.

Text
Gutknecht_2013_2.pdf - Version of Record
Available under License Creative Commons Attribution.
Download (2MB)

More information

Published date: 21 June 2013
Organisations: Geochemistry

Identifiers

Local EPrints ID: 400921
URI: http://eprints.soton.ac.uk/id/eprint/400921
ISSN: 1726-4170
PURE UUID: 9ef47e86-2e58-4af2-bc20-7d877d9d5ea7
ORCID for A. Flohr: ORCID iD orcid.org/0000-0002-5018-5379

Catalogue record

Date deposited: 29 Sep 2016 16:11
Last modified: 12 Dec 2021 04:01

Export record

Altmetrics

Contributors

Author: E. Gutknecht
Author: I. Dadou
Author: P. Marchesiello
Author: G. Cambon
Author: B. Le Vu
Author: J. Sudre
Author: V. Garçon
Author: E. Machu
Author: T. Rixen
Author: A. Kock
Author: A. Flohr ORCID iD
Author: A. Paulmier
Author: G. Lavik

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 http://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.

×