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Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study

Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study
Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study
The Mauritanian upwelling system is one of the most biologically productive regions of the world's oceans. Coastal upwelling transfers nutrients to the sun-lit surface ocean, thereby stimulating phytoplankton growth. Upwelling of deep waters also supplies dissolved inorganic carbon (DIC), high levels of which lead to low calcium carbonate saturation states in surface waters, with potentially adverse effects on marine calcifiers. In this study an upwelled filament off the coast of northwest Africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological, physical and chemical processes. The initial pHtot in the mixed layer of the upwelled plume was 7.94 and the saturation states of calcite and aragonite were 3.4 and 2.2, respectively. As the plume moved offshore over a period of 9 days, biological uptake of DIC (37 ?mol kg?1) reduced pCO2 concentrations from 540 to 410 ?atm, thereby increasing pHtot to 8.05 and calcite and aragonite saturation states to 4.0 and 2.7 respectively. The increase (25 ?mol kg?1) in total alkalinity over the 9 day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity (i.e., evaporation and mixing with other water masses). We found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers. The ongoing expansion of oxygen minimum zones through global warming will likely further reduce the CaCO3 saturation of upwelled waters, amplifying any adverse consequences of ocean acidification on the ecosystem of the Mauritanian upwelling system.
0886-6236
GB3008
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Tyrrell, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Torres, Ricardo
13e75325-69fe-415c-ad37-f9518d49fffc
Nightingale, Philip D.
4557daaa-1923-4964-b38b-f45f90d1cc28
Kitidis, Vassilis
dcefa34f-4596-4bbf-b7f8-6b3c422e2df8
Serret, Pablo
d5e253c3-633d-4ef8-9741-ef347b2ba2ab
Woodward, Malcolm
e90435b9-a070-40a0-a2ef-89b35a7b7541
Robinson, Carol
aa5b407d-ce1d-4706-a7ce-e2ee4c832071
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Tyrrell, Toby
6808411d-c9cf-47a3-88b6-c7c294f2d114
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Torres, Ricardo
13e75325-69fe-415c-ad37-f9518d49fffc
Nightingale, Philip D.
4557daaa-1923-4964-b38b-f45f90d1cc28
Kitidis, Vassilis
dcefa34f-4596-4bbf-b7f8-6b3c422e2df8
Serret, Pablo
d5e253c3-633d-4ef8-9741-ef347b2ba2ab
Woodward, Malcolm
e90435b9-a070-40a0-a2ef-89b35a7b7541
Robinson, Carol
aa5b407d-ce1d-4706-a7ce-e2ee4c832071

Loucaides, Socratis, Tyrrell, Toby, Achterberg, Eric P., Torres, Ricardo, Nightingale, Philip D., Kitidis, Vassilis, Serret, Pablo, Woodward, Malcolm and Robinson, Carol (2012) Biological and physical forcing of carbonate chemistry in an upwelling filament off northwest Africa: Results from a Lagrangian study. Global Biogeochemical Cycles, 26 (3), GB3008. (doi:10.1029/2011GB004216).

Record type: Article

Abstract

The Mauritanian upwelling system is one of the most biologically productive regions of the world's oceans. Coastal upwelling transfers nutrients to the sun-lit surface ocean, thereby stimulating phytoplankton growth. Upwelling of deep waters also supplies dissolved inorganic carbon (DIC), high levels of which lead to low calcium carbonate saturation states in surface waters, with potentially adverse effects on marine calcifiers. In this study an upwelled filament off the coast of northwest Africa was followed using drifting buoys and sulphur hexafluoride to determine how the carbonate chemistry changed over time as a result of biological, physical and chemical processes. The initial pHtot in the mixed layer of the upwelled plume was 7.94 and the saturation states of calcite and aragonite were 3.4 and 2.2, respectively. As the plume moved offshore over a period of 9 days, biological uptake of DIC (37 ?mol kg?1) reduced pCO2 concentrations from 540 to 410 ?atm, thereby increasing pHtot to 8.05 and calcite and aragonite saturation states to 4.0 and 2.7 respectively. The increase (25 ?mol kg?1) in total alkalinity over the 9 day study period can be accounted for solely by the combined effects of nitrate uptake and processes that alter salinity (i.e., evaporation and mixing with other water masses). We found no evidence of significant alkalinity accumulation as a result of exudation of organic bases by primary producers. The ongoing expansion of oxygen minimum zones through global warming will likely further reduce the CaCO3 saturation of upwelled waters, amplifying any adverse consequences of ocean acidification on the ecosystem of the Mauritanian upwelling system.

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Published date: 2012
Organisations: Ocean Biochemistry & Ecosystems

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Local EPrints ID: 343410
URI: http://eprints.soton.ac.uk/id/eprint/343410
ISSN: 0886-6236
PURE UUID: eb49175e-baee-44a7-a5b1-ed2c4a976ce6
ORCID for Toby Tyrrell: ORCID iD orcid.org/0000-0002-1002-1716

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Date deposited: 02 Oct 2012 14:27
Last modified: 15 Mar 2024 02:52

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Contributors

Author: Socratis Loucaides
Author: Toby Tyrrell ORCID iD
Author: Ricardo Torres
Author: Philip D. Nightingale
Author: Vassilis Kitidis
Author: Pablo Serret
Author: Malcolm Woodward
Author: Carol Robinson

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