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Geochemical evidence of denitrification in the Benguela upwelling system

Geochemical evidence of denitrification in the Benguela upwelling system
Geochemical evidence of denitrification in the Benguela upwelling system
This paper presents analysis of nitrate, phosphate and silicate data from the Benguela upwelling system. Evidence is presented that suggests denitrification occurring close to shore, and also nutrient trapping. Denitrification leaves an imprint on the water properties in terms of a nitrate deficit, that is to say nitrate concentrations that are significantly less than predicted by multiplying the phosphate concentrations by the Redfield ratio. It is probable that denitrification also causes a decoupling of nitrate and carbon compared to Redfield processes, and large-scale losses of nitrate in the Benguela which are not accompanied by losses of carbon. Nitrate-driven CO2 drawdown following upwelling will be less than it might otherwise be, because of denitrification.Nutrient trapping (secondary remineralisation) is apparent as enhanced phosphate concentrations, some of which are several [mu]mol higher than in the offshore source waters for upwelling. Waters also become enriched in silicate and to a lesser extent nitrate as they advect across the shelf. By implication the same process should also "supercharge" waters in dissolved inorganic carbon, leading to stronger outgassing of CO2 immediately after upwelling. The effect is again to increase the size of the estimated Benguela upwelling system CO2 source
Benguela, Denitrification, Nutrient trapping, Nitrate deficit, Nitrate, Phosphate
0278-4343
2497-2511
Tyrrell, T.
6808411d-c9cf-47a3-88b6-c7c294f2d114
Lucas, M.I.
1d860b0b-ec20-428d-afaa-0f5ca576e369
Tyrrell, T.
6808411d-c9cf-47a3-88b6-c7c294f2d114
Lucas, M.I.
1d860b0b-ec20-428d-afaa-0f5ca576e369

Tyrrell, T. and Lucas, M.I. (2002) Geochemical evidence of denitrification in the Benguela upwelling system. Continental Shelf Research, 22 (17), 2497-2511. (doi:10.1016/S0278-4343(02)00077-8).

Record type: Article

Abstract

This paper presents analysis of nitrate, phosphate and silicate data from the Benguela upwelling system. Evidence is presented that suggests denitrification occurring close to shore, and also nutrient trapping. Denitrification leaves an imprint on the water properties in terms of a nitrate deficit, that is to say nitrate concentrations that are significantly less than predicted by multiplying the phosphate concentrations by the Redfield ratio. It is probable that denitrification also causes a decoupling of nitrate and carbon compared to Redfield processes, and large-scale losses of nitrate in the Benguela which are not accompanied by losses of carbon. Nitrate-driven CO2 drawdown following upwelling will be less than it might otherwise be, because of denitrification.Nutrient trapping (secondary remineralisation) is apparent as enhanced phosphate concentrations, some of which are several [mu]mol higher than in the offshore source waters for upwelling. Waters also become enriched in silicate and to a lesser extent nitrate as they advect across the shelf. By implication the same process should also "supercharge" waters in dissolved inorganic carbon, leading to stronger outgassing of CO2 immediately after upwelling. The effect is again to increase the size of the estimated Benguela upwelling system CO2 source

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More information

Published date: 2002
Keywords: Benguela, Denitrification, Nutrient trapping, Nitrate deficit, Nitrate, Phosphate

Identifiers

Local EPrints ID: 6022
URI: http://eprints.soton.ac.uk/id/eprint/6022
ISSN: 0278-4343
PURE UUID: 2d840c24-ff06-468d-ac7a-5579cad9185b
ORCID for T. Tyrrell: ORCID iD orcid.org/0000-0002-1002-1716

Catalogue record

Date deposited: 08 Jun 2004
Last modified: 10 Nov 2021 02:49

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Contributors

Author: T. Tyrrell ORCID iD
Author: M.I. Lucas

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