First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System
The northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen cons...
Published in: | Geophysical Research Letters |
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American Geophysical Union (AGU)
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Online Access: | https://archimer.ifremer.fr/doc/00479/59020/61640.pdf https://archimer.ifremer.fr/doc/00479/59020/61641.pdf https://doi.org/10.1029/2018GL079622 https://archimer.ifremer.fr/doc/00479/59020/ |
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ftarchimer:oai:archimer.ifremer.fr:59020 2023-05-15T17:36:46+02:00 First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System Machu, Eric Capet, Xavier Estrade, Philippe Ndoye, S. Brajard, J. Baurand, Francois Auger, P.-a. Lazar, A. Brehmer, Patrice 2019-03 application/pdf https://archimer.ifremer.fr/doc/00479/59020/61640.pdf https://archimer.ifremer.fr/doc/00479/59020/61641.pdf https://doi.org/10.1029/2018GL079622 https://archimer.ifremer.fr/doc/00479/59020/ eng eng American Geophysical Union (AGU) info:eu-repo/grantAgreement/EC/FP7/603521/EU//PREFACE https://archimer.ifremer.fr/doc/00479/59020/61640.pdf https://archimer.ifremer.fr/doc/00479/59020/61641.pdf doi:10.1029/2018GL079622 https://archimer.ifremer.fr/doc/00479/59020/ info:eu-repo/semantics/openAccess restricted use Geophysical Research Letters (0094-8276) (American Geophysical Union (AGU)), 2019-03 , Vol. 46 , N. 5 , P. 2619-2627 oxygen canary upwelling system anoxia denitrification shallow continental shelf text Publication info:eu-repo/semantics/article 2019 ftarchimer https://doi.org/10.1029/2018GL079622 2021-09-23T20:32:01Z The northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. Based on circumstantial in situ observations this study demonstrates that the Senegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11 mmol/m3) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. The anoxic event was associated with a prolonged upwelling relaxation episode in March 2012 and a near shore diatom bloom that underwent degradation while being advected offshore in stratified waters. This is consistent with scenarios observed in other upwelling systems (Benguela and California) and such conditions are presumably frequent in the southern part of the Canary system. Plain Language Summary Oxygen is a key requirement for respiration by marine living organisms. Warming of the atmosphere and the ocean surface to reduces the oxygenation of offshore waters. Similarly, the extra load of nutrients from agriculture or waste waters modify algal production, particularly in coastal regionsoften resulting in oxygen‐depleted waters. Specific reactions affecting the ionic forms of nitrogen also occur within oxygen‐depleted waters also impact the nitrogen cycle by generating nitrite, which is poisonous for marine organisms, and nitrous oxide, a powerful greenhouse gas.We took measurements at sea to show that a poorly studied coastal sector of the North Atlantic Ocean, the Senegalese continental shelf, can be episodically subjected to complete depletion of subsurface oxygen (anoxia) as well as high nitrite concentrations, constituting the first report of anoxia for this oceanic region. We also show that this anoxia is likely the consequence of the decay of a bloom of diatoms, a group of microalgae common in this type of ecosystem thatinitially developed in shallow waters and transported offshore by anomalous currents associated with low‐wind conditions. Article in Journal/Newspaper North Atlantic Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) Geophysical Research Letters 46 5 2619 2627 |
institution |
Open Polar |
collection |
Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) |
op_collection_id |
ftarchimer |
language |
English |
topic |
oxygen canary upwelling system anoxia denitrification shallow continental shelf |
spellingShingle |
oxygen canary upwelling system anoxia denitrification shallow continental shelf Machu, Eric Capet, Xavier Estrade, Philippe Ndoye, S. Brajard, J. Baurand, Francois Auger, P.-a. Lazar, A. Brehmer, Patrice First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
topic_facet |
oxygen canary upwelling system anoxia denitrification shallow continental shelf |
description |
The northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. Based on circumstantial in situ observations this study demonstrates that the Senegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11 mmol/m3) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. The anoxic event was associated with a prolonged upwelling relaxation episode in March 2012 and a near shore diatom bloom that underwent degradation while being advected offshore in stratified waters. This is consistent with scenarios observed in other upwelling systems (Benguela and California) and such conditions are presumably frequent in the southern part of the Canary system. Plain Language Summary Oxygen is a key requirement for respiration by marine living organisms. Warming of the atmosphere and the ocean surface to reduces the oxygenation of offshore waters. Similarly, the extra load of nutrients from agriculture or waste waters modify algal production, particularly in coastal regionsoften resulting in oxygen‐depleted waters. Specific reactions affecting the ionic forms of nitrogen also occur within oxygen‐depleted waters also impact the nitrogen cycle by generating nitrite, which is poisonous for marine organisms, and nitrous oxide, a powerful greenhouse gas.We took measurements at sea to show that a poorly studied coastal sector of the North Atlantic Ocean, the Senegalese continental shelf, can be episodically subjected to complete depletion of subsurface oxygen (anoxia) as well as high nitrite concentrations, constituting the first report of anoxia for this oceanic region. We also show that this anoxia is likely the consequence of the decay of a bloom of diatoms, a group of microalgae common in this type of ecosystem thatinitially developed in shallow waters and transported offshore by anomalous currents associated with low‐wind conditions. |
format |
Article in Journal/Newspaper |
author |
Machu, Eric Capet, Xavier Estrade, Philippe Ndoye, S. Brajard, J. Baurand, Francois Auger, P.-a. Lazar, A. Brehmer, Patrice |
author_facet |
Machu, Eric Capet, Xavier Estrade, Philippe Ndoye, S. Brajard, J. Baurand, Francois Auger, P.-a. Lazar, A. Brehmer, Patrice |
author_sort |
Machu, Eric |
title |
First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
title_short |
First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
title_full |
First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
title_fullStr |
First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
title_full_unstemmed |
First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System |
title_sort |
first evidence of anoxia and nitrogen loss in the southern canary upwelling system |
publisher |
American Geophysical Union (AGU) |
publishDate |
2019 |
url |
https://archimer.ifremer.fr/doc/00479/59020/61640.pdf https://archimer.ifremer.fr/doc/00479/59020/61641.pdf https://doi.org/10.1029/2018GL079622 https://archimer.ifremer.fr/doc/00479/59020/ |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Geophysical Research Letters (0094-8276) (American Geophysical Union (AGU)), 2019-03 , Vol. 46 , N. 5 , P. 2619-2627 |
op_relation |
info:eu-repo/grantAgreement/EC/FP7/603521/EU//PREFACE https://archimer.ifremer.fr/doc/00479/59020/61640.pdf https://archimer.ifremer.fr/doc/00479/59020/61641.pdf doi:10.1029/2018GL079622 https://archimer.ifremer.fr/doc/00479/59020/ |
op_rights |
info:eu-repo/semantics/openAccess restricted use |
op_doi |
https://doi.org/10.1029/2018GL079622 |
container_title |
Geophysical Research Letters |
container_volume |
46 |
container_issue |
5 |
container_start_page |
2619 |
op_container_end_page |
2627 |
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1766136357791465472 |