Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic
Sustaining biological export over the open ocean requires a physical supply of nutrients to the mixed layer and thermocline. The relative importance of diapycnal mixing, diapycnal advection and isopycnal stirring by mesoscale eddies in providing this nutrient supply is explored using a field campaig...
Published in: | Global Biogeochemical Cycles |
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Main Authors: | , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
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American Geophysical Union (AGU)
2021
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Online Access: | https://archimer.ifremer.fr/doc/00736/84803/89842.pdf https://doi.org/10.1029/2021GB007200 https://archimer.ifremer.fr/doc/00736/84803/ |
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ftarchimer:oai:archimer.ifremer.fr:84803 2023-05-15T17:29:02+02:00 Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic Spingys, Carl P. Williams, Richard G. Tuerena, Robyn E. Garabato, Alberto Naveira Vic, Clement Forryan, Alexander Sharples, Jonathan 2021-12 application/pdf https://archimer.ifremer.fr/doc/00736/84803/89842.pdf https://doi.org/10.1029/2021GB007200 https://archimer.ifremer.fr/doc/00736/84803/ eng eng American Geophysical Union (AGU) https://archimer.ifremer.fr/doc/00736/84803/89842.pdf doi:10.1029/2021GB007200 https://archimer.ifremer.fr/doc/00736/84803/ info:eu-repo/semantics/openAccess restricted use Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2021-12 , Vol. 35 , N. 12 , P. e2021GB007200 (20p.) Nutrient supply Diapycnic mixing Diapycnic advection Mesoscale eddies Isopycnal stirring North Atlantic text Publication info:eu-repo/semantics/article 2021 ftarchimer https://doi.org/10.1029/2021GB007200 2022-01-11T23:50:32Z Sustaining biological export over the open ocean requires a physical supply of nutrients to the mixed layer and thermocline. The relative importance of diapycnal mixing, diapycnal advection and isopycnal stirring by mesoscale eddies in providing this nutrient supply is explored using a field campaign in oligotrophic waters in the subtropical North Atlantic, consisting of transects over and off the mid-Atlantic ridge. Eddy stirring rates are estimated from the excess temperature variance dissipation relative to the turbulent kinetic energy dissipation, and using eddy statistics from satellite observations combined with 9-month-long mooring data. The vertical nutrient fluxes by diapycnal mixing, diapycnal advection and isopycnal mesoscale eddy stirring are assessed using nitrate measurements from observations or a climatology. Diapycnal mixing and advection provide a nutrient supply within the euphotic zone, but a loss of nutrients within the upper thermocline. Eddy stirring augments, and is comparable to, the diapycnal transfer of nutrients within the summertime upper thermocline, while also acting to replenish nutrients within the deeper parts of the thermocline. The eddy supply of nitrate is relatively small in the centre of the subtropical gyre, reaching up to 0.06 mol N m−2yr−1, but is likely to be enhanced on the flanks of the gyre due to larger isopycnal slopes and lateral nitrate gradients. The nutrient supply to the euphotic zone is achieved via a multi-stage mechanism: a diapycnal transfer of nutrients by small-scale turbulence to the euphotic zone, and an isopycnal stirring of nutrients by mesoscale eddies replenishing nutrients in the upper thermocline. Plain Language Summary Phytoplankton growth requires a supply of nutrients to the base of the euphotic zone, which is usually provided by a combination of vertical mixing or vertical upwelling of nutrients. However, in the oligotrophic waters of the central North Atlantic, it is unclear how the vertical supply of nutrients is sustained. Here we use field data to explore the roles of mixing across density surfaces, advection across density surfaces and mesoscale eddy stirring along density surfaces in supplying nutrients to some of the most nutrient-depleted surface waters in the central North Atlantic. Diapycnal mixing and advection are found to be important in supplying nutrients to the euphotic zone during summer, but at the expense of eroding the nutrients in the upper thermocline. In contrast, mesoscale eddy stirring augments the diapycnal supply of nutrients to the euphotic zone, and replenishes nutrients in the upper thermocline. Article in Journal/Newspaper North Atlantic Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) Mid-Atlantic Ridge Global Biogeochemical Cycles |
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 |
Nutrient supply Diapycnic mixing Diapycnic advection Mesoscale eddies Isopycnal stirring North Atlantic |
spellingShingle |
Nutrient supply Diapycnic mixing Diapycnic advection Mesoscale eddies Isopycnal stirring North Atlantic Spingys, Carl P. Williams, Richard G. Tuerena, Robyn E. Garabato, Alberto Naveira Vic, Clement Forryan, Alexander Sharples, Jonathan Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
topic_facet |
Nutrient supply Diapycnic mixing Diapycnic advection Mesoscale eddies Isopycnal stirring North Atlantic |
description |
Sustaining biological export over the open ocean requires a physical supply of nutrients to the mixed layer and thermocline. The relative importance of diapycnal mixing, diapycnal advection and isopycnal stirring by mesoscale eddies in providing this nutrient supply is explored using a field campaign in oligotrophic waters in the subtropical North Atlantic, consisting of transects over and off the mid-Atlantic ridge. Eddy stirring rates are estimated from the excess temperature variance dissipation relative to the turbulent kinetic energy dissipation, and using eddy statistics from satellite observations combined with 9-month-long mooring data. The vertical nutrient fluxes by diapycnal mixing, diapycnal advection and isopycnal mesoscale eddy stirring are assessed using nitrate measurements from observations or a climatology. Diapycnal mixing and advection provide a nutrient supply within the euphotic zone, but a loss of nutrients within the upper thermocline. Eddy stirring augments, and is comparable to, the diapycnal transfer of nutrients within the summertime upper thermocline, while also acting to replenish nutrients within the deeper parts of the thermocline. The eddy supply of nitrate is relatively small in the centre of the subtropical gyre, reaching up to 0.06 mol N m−2yr−1, but is likely to be enhanced on the flanks of the gyre due to larger isopycnal slopes and lateral nitrate gradients. The nutrient supply to the euphotic zone is achieved via a multi-stage mechanism: a diapycnal transfer of nutrients by small-scale turbulence to the euphotic zone, and an isopycnal stirring of nutrients by mesoscale eddies replenishing nutrients in the upper thermocline. Plain Language Summary Phytoplankton growth requires a supply of nutrients to the base of the euphotic zone, which is usually provided by a combination of vertical mixing or vertical upwelling of nutrients. However, in the oligotrophic waters of the central North Atlantic, it is unclear how the vertical supply of nutrients is sustained. Here we use field data to explore the roles of mixing across density surfaces, advection across density surfaces and mesoscale eddy stirring along density surfaces in supplying nutrients to some of the most nutrient-depleted surface waters in the central North Atlantic. Diapycnal mixing and advection are found to be important in supplying nutrients to the euphotic zone during summer, but at the expense of eroding the nutrients in the upper thermocline. In contrast, mesoscale eddy stirring augments the diapycnal supply of nutrients to the euphotic zone, and replenishes nutrients in the upper thermocline. |
format |
Article in Journal/Newspaper |
author |
Spingys, Carl P. Williams, Richard G. Tuerena, Robyn E. Garabato, Alberto Naveira Vic, Clement Forryan, Alexander Sharples, Jonathan |
author_facet |
Spingys, Carl P. Williams, Richard G. Tuerena, Robyn E. Garabato, Alberto Naveira Vic, Clement Forryan, Alexander Sharples, Jonathan |
author_sort |
Spingys, Carl P. |
title |
Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
title_short |
Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
title_full |
Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
title_fullStr |
Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
title_full_unstemmed |
Observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic North Atlantic |
title_sort |
observations of nutrient supply by mesoscale eddy stirring and small‐scale turbulence in the oligotrophic north atlantic |
publisher |
American Geophysical Union (AGU) |
publishDate |
2021 |
url |
https://archimer.ifremer.fr/doc/00736/84803/89842.pdf https://doi.org/10.1029/2021GB007200 https://archimer.ifremer.fr/doc/00736/84803/ |
geographic |
Mid-Atlantic Ridge |
geographic_facet |
Mid-Atlantic Ridge |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2021-12 , Vol. 35 , N. 12 , P. e2021GB007200 (20p.) |
op_relation |
https://archimer.ifremer.fr/doc/00736/84803/89842.pdf doi:10.1029/2021GB007200 https://archimer.ifremer.fr/doc/00736/84803/ |
op_rights |
info:eu-repo/semantics/openAccess restricted use |
op_doi |
https://doi.org/10.1029/2021GB007200 |
container_title |
Global Biogeochemical Cycles |
_version_ |
1766122342269845504 |