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Summertime increases in upper ocean stratification and mixed layer depth

The surface mixed layer of the world ocean regulates global climate by controlling heat and carbon exchanges between the atmosphere and the oceanic interior(1–3). The mixed layer also shapes marine ecosystems by hosting most of the ocean’s primary production(4) and providing the conduit for oxygenat...

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Autores principales: Sallee, Jean-Baptiste, Pellichero, Violaine, Akhoudas, Camille, Pauthenet, Etienne, Vignes, Lucie, Schmidtko, Sunke, Garabato, Alberto Naveira, Sutherland, Peter, Kuusela, Mikael
Formato: Online Artículo Texto
Lenguaje:English
Publicado: 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7610469/
https://www.ncbi.nlm.nih.gov/pubmed/33762764
http://dx.doi.org/10.1038/s41586-021-03303-x
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author Sallee, Jean-Baptiste
Pellichero, Violaine
Akhoudas, Camille
Pauthenet, Etienne
Vignes, Lucie
Schmidtko, Sunke
Garabato, Alberto Naveira
Sutherland, Peter
Kuusela, Mikael
author_facet Sallee, Jean-Baptiste
Pellichero, Violaine
Akhoudas, Camille
Pauthenet, Etienne
Vignes, Lucie
Schmidtko, Sunke
Garabato, Alberto Naveira
Sutherland, Peter
Kuusela, Mikael
author_sort Sallee, Jean-Baptiste
collection PubMed
description The surface mixed layer of the world ocean regulates global climate by controlling heat and carbon exchanges between the atmosphere and the oceanic interior(1–3). The mixed layer also shapes marine ecosystems by hosting most of the ocean’s primary production(4) and providing the conduit for oxygenation of deep oceanic layers. Despite these important climatic and life-supporting roles, possible changes in the mixed layer during an era of global climate change remain uncertain. Here, we use oceanographic observations to show that from 1970-2018 the density contrast across the mixed-layer base increased and that the mixed layer itself deepened. The summertime density contrast increased by 8.9±2.7% dec(-1) (10(-6)-10(-5) s(-2) dec(-1), depending on region), more than six times greater than previous estimates due to our use of a more physically-based definition of mixed layer stability following the differing dynamical regimes across the global ocean. While prior work has suggested that a thinner mixed layer should accompany a more stratified ocean(5–7), we instead find that the summertime mixed layer deepened by 2.9±0.5% dec(-1) or several meters per decade (typically 5-10m dec(-1), depending on region). A detailed mechanistic interpretation is challenging, but the concurrent stratification and deepening of the mixed layer are related to an increase in stability associated with surface warming and high latitude surface freshening(8,9), accompanied by a wind-driven intensification of upper-ocean turbulence(10,11). Our results are based on a complex dataset with incomplete coverage of a vast area; we found our results to be robust within a wide range of sensitivity analyses, but important uncertainties remain, such as sparse coverage in the early years. Nonetheless, our work calls for reconsideration of the drivers of ongoing shifts in marine primary production, and reveals stark changes in the world’s upper ocean over the past five decades.
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spelling pubmed-76104692021-09-24 Summertime increases in upper ocean stratification and mixed layer depth Sallee, Jean-Baptiste Pellichero, Violaine Akhoudas, Camille Pauthenet, Etienne Vignes, Lucie Schmidtko, Sunke Garabato, Alberto Naveira Sutherland, Peter Kuusela, Mikael Nature Article The surface mixed layer of the world ocean regulates global climate by controlling heat and carbon exchanges between the atmosphere and the oceanic interior(1–3). The mixed layer also shapes marine ecosystems by hosting most of the ocean’s primary production(4) and providing the conduit for oxygenation of deep oceanic layers. Despite these important climatic and life-supporting roles, possible changes in the mixed layer during an era of global climate change remain uncertain. Here, we use oceanographic observations to show that from 1970-2018 the density contrast across the mixed-layer base increased and that the mixed layer itself deepened. The summertime density contrast increased by 8.9±2.7% dec(-1) (10(-6)-10(-5) s(-2) dec(-1), depending on region), more than six times greater than previous estimates due to our use of a more physically-based definition of mixed layer stability following the differing dynamical regimes across the global ocean. While prior work has suggested that a thinner mixed layer should accompany a more stratified ocean(5–7), we instead find that the summertime mixed layer deepened by 2.9±0.5% dec(-1) or several meters per decade (typically 5-10m dec(-1), depending on region). A detailed mechanistic interpretation is challenging, but the concurrent stratification and deepening of the mixed layer are related to an increase in stability associated with surface warming and high latitude surface freshening(8,9), accompanied by a wind-driven intensification of upper-ocean turbulence(10,11). Our results are based on a complex dataset with incomplete coverage of a vast area; we found our results to be robust within a wide range of sensitivity analyses, but important uncertainties remain, such as sparse coverage in the early years. Nonetheless, our work calls for reconsideration of the drivers of ongoing shifts in marine primary production, and reveals stark changes in the world’s upper ocean over the past five decades. 2021-03-01 2021-03-24 /pmc/articles/PMC7610469/ /pubmed/33762764 http://dx.doi.org/10.1038/s41586-021-03303-x Text en Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms
spellingShingle Article
Sallee, Jean-Baptiste
Pellichero, Violaine
Akhoudas, Camille
Pauthenet, Etienne
Vignes, Lucie
Schmidtko, Sunke
Garabato, Alberto Naveira
Sutherland, Peter
Kuusela, Mikael
Summertime increases in upper ocean stratification and mixed layer depth
title Summertime increases in upper ocean stratification and mixed layer depth
title_full Summertime increases in upper ocean stratification and mixed layer depth
title_fullStr Summertime increases in upper ocean stratification and mixed layer depth
title_full_unstemmed Summertime increases in upper ocean stratification and mixed layer depth
title_short Summertime increases in upper ocean stratification and mixed layer depth
title_sort summertime increases in upper ocean stratification and mixed layer depth
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7610469/
https://www.ncbi.nlm.nih.gov/pubmed/33762764
http://dx.doi.org/10.1038/s41586-021-03303-x
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