Researchers from the National Center for Scientific Research (CNRS), from Sorbonne University and the French Research Institute for the Exploitation of the Sea (Ifremer), come to highlight the consequences of climate change and human activities (called “anthropogenic”) on the ocean and marine life, as well as the future capacity of the ocean to play its role of global thermostat .
In the journal “Nature”
Of capital importance, this work was published on Wednesday March 24, 2021, in the reference journal Nature , détaillés par l’article « Summertime increases in upper ocean stratification and mixed layer depth ».
They are the result of an international collaboration, bringing together scientists from two French laboratories: on the one hand, the Oceanography and Climate Laboratory (Locean) / experiments and numerical approaches, mixed research unit bringing together CNRS, Research Institute for Development (WRITE), National Museum of Natural History (MNHN) and Sorbonne University.
And, on the other hand, the Physical and Spatial Oceanography Laboratory (Lops), a mixed research unit bringing together CNRS, Ifremer, WRITE and University of Western Brittany (UBO).
The oceanographic vessel “Marion Dufresne”, sailing in the Southern Indian Ocean. © FRED PLANCHON / UBO-LEMAR
The dynamic nature of the ocean
Remember that the ocean “is dynamic in nature, which gives it a fundamental role as a planetary thermostat mitigating global warming”.
However, as the publication explains, “In response to climate change, the ocean has tended to stabilize more and more over the past 50 years, at a rate six times greater than past estimates. “
Like water on oil
The reason for this trend? “The warming of the waters, the melting of glaciers and the disruption of precipitation form a layer on the surface of the ocean which is separated from the depths: like water on oil, this separation limits the oceanic mixing and makes climate change mitigation by the ocean more difficult. “
Otherwise, “Climate change is leading to an intensification of winds which have thickened the ocean’s surface layer by 5 to 10 m per decade for 50 years, making vital access to light more difficult for the majority of living marine biodiversity in this layer ”.
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On this idealized diagram of the world ocean, we observe the new barrier between surface ocean and deep ocean, due to climate change. However, this barrier is increasingly difficult to cross. © JEAN-BAPTISTE SALLÉE / LOCEAN (CNRS / MNHN / IRD / SORBONNE UNIVERSITY)
To illustrate his point, Jean-Baptiste Sallée presents an idealized (and edifying) diagram of the vertical structure of the global ocean.
“Mixed by winds, the surface layer absorbs atmospheric heat that increases in response to climate change. “
However, for the ocean to play a climate change mitigation role, this heat must be transmitted into the deep ocean, far from the atmosphere.
Only, “The ocean has stabilized for 50 years, with a barrier between surface ocean and deep ocean that is increasingly difficult to cross. At the same time, the intensification of the winds deepens the surface layer. “
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