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
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Emeis, Kay-Christian
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Flohr, Anita
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Rixen, Tim
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Schlarbaum, Tim
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Mohrholz, Volker
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van der Plas, Anja
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March 2013
Nagel, Birgit
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Emeis, Kay-Christian
12a66b4a-3a7b-4fc5-8951-bfaa93e1d13e
Flohr, Anita
1e293a22-bdba-408e-9608-fed8b65e4e79
Rixen, Tim
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Schlarbaum, Tim
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Mohrholz, Volker
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van der Plas, Anja
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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), .
(doi:10.1002/jgrg.20040).
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.
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Nagel_et_al-2013-Journal_of_Geophysical_Research__Biogeosciences.pdf
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Published date: March 2013
Organisations:
Geochemistry
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Local EPrints ID: 400919
URI: http://eprints.soton.ac.uk/id/eprint/400919
PURE UUID: 7bafb3e2-7448-4cc3-b134-8e4af866314c
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Date deposited: 29 Sep 2016 16:02
Last modified: 15 Mar 2024 02:32
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Author:
Birgit Nagel
Author:
Kay-Christian Emeis
Author:
Anita Flohr
Author:
Tim Rixen
Author:
Tim Schlarbaum
Author:
Volker Mohrholz
Author:
Anja van der Plas
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