The University of Southampton
University of Southampton Institutional Repository

N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf - an isotope-based approach

N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf - an isotope-based approach
N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf - an isotope-based approach
The northern Benguela upwelling system is a nutrient-replete region with high plankton biomass production and a seasonally changing oxygen minimum zone. Nitrate:phosphate ratios in fresh upwelling water are low due to denitrification in the near-seafloor oxygen minimum zone and phosphate efflux from sediments. This makes the region a candidate for substantial dinitrogen fixation, for which evidence is scarce. Nutrient and oxygen data, N isotope data of nitrate, nitrogen isotope ratios of particulate matter, particulate organic carbon content, and suspended matter concentrations on a transect across the shelf and upper slope at 23°S illustrate N-cycling processes and are the basis for estimating the contribution of N-sources and N-sinks to the reactive nitrogen pool. It appears that N-removal due to denitrification exceeds N gain by N2 fixation and physical mixing processes by a factor of >6, although inorganic N:P ratios again increase as surface water is advected offshore. Nitrate and ammonium regeneration, nutrient assimilation with N:P < 16, shelf break mixing, atmospheric input, and N2 fixation all contribute to the restoration of inorganic N:P ratios back to Redfield conditions, but in seasonally changing proportions. The Benguela upwelling system thus is a nutrient source for the oceanic-mixed layer where N-sources and N-sinks are not in balance and Redfield conditions can only re-adjust by advection and mixing processes integrated over time.
361-371
Nagel, Birgit
6d9be1ae-a8ed-4c4f-b812-2b1eb09ebf6f
Emeis, Kay-Christian
12a66b4a-3a7b-4fc5-8951-bfaa93e1d13e
Flohr, Anita
1e293a22-bdba-408e-9608-fed8b65e4e79
Rixen, Tim
d4879ffd-ed18-4795-b579-48064a113ade
Schlarbaum, Tim
9356c21a-1200-49b1-a0d6-78701f7f724f
Mohrholz, Volker
25a7de89-0f75-499b-b1d1-a9834ba2b7a7
van der Plas, Anja
8261378d-cd3b-4bda-b9af-f9099894ec6c
Nagel, Birgit
6d9be1ae-a8ed-4c4f-b812-2b1eb09ebf6f
Emeis, Kay-Christian
12a66b4a-3a7b-4fc5-8951-bfaa93e1d13e
Flohr, Anita
1e293a22-bdba-408e-9608-fed8b65e4e79
Rixen, Tim
d4879ffd-ed18-4795-b579-48064a113ade
Schlarbaum, Tim
9356c21a-1200-49b1-a0d6-78701f7f724f
Mohrholz, Volker
25a7de89-0f75-499b-b1d1-a9834ba2b7a7
van der Plas, Anja
8261378d-cd3b-4bda-b9af-f9099894ec6c

Nagel, Birgit, Emeis, Kay-Christian, Flohr, Anita, Rixen, Tim, Schlarbaum, Tim, Mohrholz, Volker and van der Plas, Anja (2013) N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf - an isotope-based approach. Journal of Geophysical Research: Biogeosciences, 118 (1), 361-371. (doi:10.1002/jgrg.20040).

Record type: Article

Abstract

The northern Benguela upwelling system is a nutrient-replete region with high plankton biomass production and a seasonally changing oxygen minimum zone. Nitrate:phosphate ratios in fresh upwelling water are low due to denitrification in the near-seafloor oxygen minimum zone and phosphate efflux from sediments. This makes the region a candidate for substantial dinitrogen fixation, for which evidence is scarce. Nutrient and oxygen data, N isotope data of nitrate, nitrogen isotope ratios of particulate matter, particulate organic carbon content, and suspended matter concentrations on a transect across the shelf and upper slope at 23°S illustrate N-cycling processes and are the basis for estimating the contribution of N-sources and N-sinks to the reactive nitrogen pool. It appears that N-removal due to denitrification exceeds N gain by N2 fixation and physical mixing processes by a factor of >6, although inorganic N:P ratios again increase as surface water is advected offshore. Nitrate and ammonium regeneration, nutrient assimilation with N:P < 16, shelf break mixing, atmospheric input, and N2 fixation all contribute to the restoration of inorganic N:P ratios back to Redfield conditions, but in seasonally changing proportions. The Benguela upwelling system thus is a nutrient source for the oceanic-mixed layer where N-sources and N-sinks are not in balance and Redfield conditions can only re-adjust by advection and mixing processes integrated over time.

Text
Nagel_et_al-2013-Journal_of_Geophysical_Research__Biogeosciences.pdf - Version of Record
Download (473kB)

More information

Published date: March 2013
Organisations: Geochemistry

Identifiers

Local EPrints ID: 400919
URI: http://eprints.soton.ac.uk/id/eprint/400919
PURE UUID: 7bafb3e2-7448-4cc3-b134-8e4af866314c
ORCID for Anita Flohr: ORCID iD orcid.org/0000-0002-5018-5379

Catalogue record

Date deposited: 29 Sep 2016 16:02
Last modified: 09 Jan 2022 03:45

Export record

Altmetrics

Contributors

Author: Birgit Nagel
Author: Kay-Christian Emeis
Author: Anita Flohr ORCID iD
Author: Tim Rixen
Author: Tim Schlarbaum
Author: Volker Mohrholz
Author: Anja van der Plas

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.

×