Les océans se mélangent beaucoup moins que prévu sous l’effet du changement climatique
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How Climate Change is Affecting our Oceans

An international research team including researchers from CNRS, Sorbonne University and Ifremer has demonstrated that the ocean is increasingly moving towards stabilization. This work was published on March 24, 2021 in Nature.

The ocean is dynamic in nature, which gives it a fundamental role as a global thermostat mitigating global warming. However, in response to climate change, the ocean has been increasingly stabilizing over the past 50 years, at a rate six times greater than previously estimated. This has been shown by a study conducted by researchers from CNRS, Sorbonne University, and Ifremer as part of an international collaboration1 .

Warming waters, melting glaciers and disrupted precipitation form a layer on the ocean surface that decouples from the deep ocean: like water on oil, this separation limits ocean mixing and makes it more difficult for the ocean to mitigate climate change.

In addition, climate change is causing winds to intensify, which has thickened the surface layer of the ocean by 5-10 meters per decade for the past 50 years, making it more difficult for the majority of marine biodiversity living in this layer to gain vital access to light.

Published on March 24, 2021 in Nature, this work highlights the consequences of climate change and human activities on the ocean and marine life, as well as the future ability of the ocean to play its role as a global thermostat.

Basic diagram of the ocean's vertical structure: The surface layer is mixed by wind, and absorbs atmospheric heat that increases in response to climate change. For the ocean to play a role in mitigating climate change, this heat must be transferred to the deep ocean, away from the atmosphere. But the ocean has been stabilizing for the past 50 years, with a barrier between the surface and deep oceans that is increasingly difficult to cross. At the same time, the intensification of winds deepens the surface layer.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N°821001.

1 The French laboratories involved are the Laboratoire d'océanographie et du climat: expérimentations et approches numériques (CNRS/IRD/MNHN/Sorbonne University) and the Laboratoire d'océanographie physique et spatiale (CNRS/Ifremer/IRD/Université de Bretagne occidentale).
Reference

References

Summertime increases in upper ocean stratification and mixed layer depth. Sallée J.B., Pellichero V., Akhoudas C., Pauthenet E., Vignes L., Schmidtko S., Naveira Garabato A., Sutherland P. and Kuusela M. Nature, March 24, 2021

DOI : https://dx.doi.org/10.1038/s41586-021-03303-x

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