Global warming weakens the South Atlantic circulation

THE environmental changes of anthropogenic origin in the vicinity of Antarctica contribute to sea level rise in the North Atlantic. A fact that would lead to the collapse of the Atlantic Southern Circulation (Amoc), sending the planet towards possible glaciation. This is according to a study published in the journal Nature Geoscience, conducted by scientists from the University of Miami’s Rosenstiel School of Marine Atmospheric and Earth Science and the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory. A team led by Tiago Bilò analyzed deep hydrographic data collected from observational mooring programs collected over two decades. The survey revealed that the Atlantic meridional circulation has weakened by about 12 percent over the past 20 years.

“Although the studied Arctic and Atlantic regions are tens of thousands of kilometers apart – emphasizes Bilò – our results confirm the idea that even the most remote areas of the world’s oceans are vulnerable to climate change associated with human activity.” “The areas affected by this warming span thousands of kilometers – emphasizes William Johns, co-author of the article – 4000 and 6000 meters deep. As a result, there is a significant increase in the heat content of the deep ocean, which is contributed by the local rise of the sea level due to the thermal expansion of water”. “Our observational analysis – concludes Bilò – confirms what the numerical models predicted: human activity could potentially cause changes in the circulation of the entire ocean.”

As part of the DeepT (Innovative Analysis of Deep and Abyssal Temperature from a Bottom-Anchored Instrument) project, the research team analyzed data from several observing programs to study changes over time in the cold, dense, deep mass, located at depths greater than 4,000 meters below the surface of the ocean that flows from the Southern Ocean northward and up into other parts of the world such as the North Atlantic. This dynamic is part of a phenomenon known as the Atlantic Southern Circulation (Amoc), a three-dimensional system of ocean currents that contributes to the distribution of heat, nutrients and carbon in the ocean. As sea ice forms, it releases salt, increasing the density of the surrounding water, which then tends to sink, creating a colder, denser layer that spreads northward. During the 21st century, a temperature redistribution phenomenon was observed, cooler in the higher latitudes and milder in the deep oceans.

In short, global warming undermines the exchange of heat between ocean currents, with consequences that can be devastating. Seas swell with fresh water produced by melting Antarctic ice. In Europe, temperatures would drop drastically and glacial scenarios would open up for the entire northern hemisphere of the world. Now the circulation loss equals 12%, it remains to be understood whether this process is now irreversible or not.


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