?Mixing and Transformation in a Deep Western Boundary Current: A Case Study
International audience Water-mass transformation by turbulent mixing is a key part of the deep-ocean overturning, as it drives the upwelling of dense waters formed at high latitudes. Here, we quantify this transformation and its underpinning processes in a small Southern Ocean basin: the Orkney Deep...
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2021
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ftunivbrest:oai:HAL:insu-03683270v1 2024-04-14T08:20:03+00:00 ?Mixing and Transformation in a Deep Western Boundary Current: A Case Study Spingys, Carl P. Naveira Garabato, Alberto C. Legg, Sonya Polzin, Kurt L. Abrahamsen, E. Povl Buckingham, Christian E. Forryan, Alexander Frajka-Williams, Eleanor E. Laboratoire d'Océanographie Physique et Spatiale (LOPS) Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS) 2021 https://insu.hal.science/insu-03683270 https://insu.hal.science/insu-03683270/document https://insu.hal.science/insu-03683270/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20Mixing%20and%20Transformation%20in%20a%20Deep%20Western%20Boundary%20Current%20A%20Case%20Study.pdf https://doi.org/10.1175/JPO-D-20-0132.1 en eng HAL CCSD info:eu-repo/semantics/altIdentifier/doi/10.1175/JPO-D-20-0132.1 insu-03683270 https://insu.hal.science/insu-03683270 https://insu.hal.science/insu-03683270/document https://insu.hal.science/insu-03683270/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20Mixing%20and%20Transformation%20in%20a%20Deep%20Western%20Boundary%20Current%20A%20Case%20Study.pdf BIBCODE: 2021JPO.51.1205S doi:10.1175/JPO-D-20-0132.1 http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess JOURNAL OF PHYSICAL OCEANOGRAPHY https://insu.hal.science/insu-03683270 JOURNAL OF PHYSICAL OCEANOGRAPHY, 2021, 51, pp.1205-1222. ⟨10.1175/JPO-D-20-0132.1⟩ [SDU]Sciences of the Universe [physics] [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography info:eu-repo/semantics/article Journal articles 2021 ftunivbrest https://doi.org/10.1175/JPO-D-20-0132.1 2024-03-21T16:24:19Z International audience Water-mass transformation by turbulent mixing is a key part of the deep-ocean overturning, as it drives the upwelling of dense waters formed at high latitudes. Here, we quantify this transformation and its underpinning processes in a small Southern Ocean basin: the Orkney Deep. Observations reveal a focusing of the transport in density space as a deep western boundary current (DWBC) flows through the region, associated with lightening and densification of the current's denser and lighter layers, respectively. These transformations are driven by vigorous turbulent mixing. Comparing this transformation with measurements of the rate of turbulent kinetic energy dissipation indicates that, within the DWBC, turbulence operates with a high mixing efficiency, characterized by a dissipation ratio of 0.6 to 1 that exceeds the common value of 0.2. This result is corroborated by estimates of the dissipation ratio from microstructure observations. The causes of the transformation are unraveled through a decomposition into contributions dependent on the gradients in density space of the: dianeutral mixing rate, isoneutral area, and stratification. The transformation is found to be primarily driven by strong turbulence acting on an abrupt transition from the weakly stratified bottom boundary layer to well-stratified off-boundary waters. The reduced boundary layer stratification is generated by a downslope Ekman flow associated with the DWBC's flow along sloping topography, and is further regulated by submesoscale instabilities acting to restratify near-boundary waters. Our results provide observational evidence endorsing the importance of near-boundary mixing processes to deep-ocean overturning, and highlight the role of DWBCs as hot spots of dianeutral upwelling. Article in Journal/Newspaper Southern Ocean Université de Bretagne Occidentale: HAL Southern Ocean Journal of Physical Oceanography 51 4 1205 1222 |
institution |
Open Polar |
collection |
Université de Bretagne Occidentale: HAL |
op_collection_id |
ftunivbrest |
language |
English |
topic |
[SDU]Sciences of the Universe [physics] [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography |
spellingShingle |
[SDU]Sciences of the Universe [physics] [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography Spingys, Carl P. Naveira Garabato, Alberto C. Legg, Sonya Polzin, Kurt L. Abrahamsen, E. Povl Buckingham, Christian E. Forryan, Alexander Frajka-Williams, Eleanor E. ?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
topic_facet |
[SDU]Sciences of the Universe [physics] [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography |
description |
International audience Water-mass transformation by turbulent mixing is a key part of the deep-ocean overturning, as it drives the upwelling of dense waters formed at high latitudes. Here, we quantify this transformation and its underpinning processes in a small Southern Ocean basin: the Orkney Deep. Observations reveal a focusing of the transport in density space as a deep western boundary current (DWBC) flows through the region, associated with lightening and densification of the current's denser and lighter layers, respectively. These transformations are driven by vigorous turbulent mixing. Comparing this transformation with measurements of the rate of turbulent kinetic energy dissipation indicates that, within the DWBC, turbulence operates with a high mixing efficiency, characterized by a dissipation ratio of 0.6 to 1 that exceeds the common value of 0.2. This result is corroborated by estimates of the dissipation ratio from microstructure observations. The causes of the transformation are unraveled through a decomposition into contributions dependent on the gradients in density space of the: dianeutral mixing rate, isoneutral area, and stratification. The transformation is found to be primarily driven by strong turbulence acting on an abrupt transition from the weakly stratified bottom boundary layer to well-stratified off-boundary waters. The reduced boundary layer stratification is generated by a downslope Ekman flow associated with the DWBC's flow along sloping topography, and is further regulated by submesoscale instabilities acting to restratify near-boundary waters. Our results provide observational evidence endorsing the importance of near-boundary mixing processes to deep-ocean overturning, and highlight the role of DWBCs as hot spots of dianeutral upwelling. |
author2 |
Laboratoire d'Océanographie Physique et Spatiale (LOPS) Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS) |
format |
Article in Journal/Newspaper |
author |
Spingys, Carl P. Naveira Garabato, Alberto C. Legg, Sonya Polzin, Kurt L. Abrahamsen, E. Povl Buckingham, Christian E. Forryan, Alexander Frajka-Williams, Eleanor E. |
author_facet |
Spingys, Carl P. Naveira Garabato, Alberto C. Legg, Sonya Polzin, Kurt L. Abrahamsen, E. Povl Buckingham, Christian E. Forryan, Alexander Frajka-Williams, Eleanor E. |
author_sort |
Spingys, Carl P. |
title |
?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
title_short |
?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
title_full |
?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
title_fullStr |
?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
title_full_unstemmed |
?Mixing and Transformation in a Deep Western Boundary Current: A Case Study |
title_sort |
?mixing and transformation in a deep western boundary current: a case study |
publisher |
HAL CCSD |
publishDate |
2021 |
url |
https://insu.hal.science/insu-03683270 https://insu.hal.science/insu-03683270/document https://insu.hal.science/insu-03683270/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20Mixing%20and%20Transformation%20in%20a%20Deep%20Western%20Boundary%20Current%20A%20Case%20Study.pdf https://doi.org/10.1175/JPO-D-20-0132.1 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
JOURNAL OF PHYSICAL OCEANOGRAPHY https://insu.hal.science/insu-03683270 JOURNAL OF PHYSICAL OCEANOGRAPHY, 2021, 51, pp.1205-1222. ⟨10.1175/JPO-D-20-0132.1⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1175/JPO-D-20-0132.1 insu-03683270 https://insu.hal.science/insu-03683270 https://insu.hal.science/insu-03683270/document https://insu.hal.science/insu-03683270/file/%5B15200485%20-%20Journal%20of%20Physical%20Oceanography%5D%20Mixing%20and%20Transformation%20in%20a%20Deep%20Western%20Boundary%20Current%20A%20Case%20Study.pdf BIBCODE: 2021JPO.51.1205S doi:10.1175/JPO-D-20-0132.1 |
op_rights |
http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess |
op_doi |
https://doi.org/10.1175/JPO-D-20-0132.1 |
container_title |
Journal of Physical Oceanography |
container_volume |
51 |
container_issue |
4 |
container_start_page |
1205 |
op_container_end_page |
1222 |
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1796298238491361280 |