The Atlantic Ocean in turmoil: how marine heat waves put the environment at risk!

The seas are on fire! Between March and May 2023, average temperatures measured at the surface of the oceans reached a record high, exceeding the average recorded in the 20th century by 0.83 degrees, according to the United States Oceanographic Administration.

The heat wave was particularly intense from one end of the Atlantic Ocean to the other. Temperature anomalies of up to 5 degrees were recorded off the British Isles in June.

"Such temperature anomalies in this part of the North Atlantic are unheard of," said Daniela Schmidt, a professor at the University of Bristol, quoted by the British Science Media Centre.

Words confirmed by Jean-Baptiste Sallée, oceanographer and climatologist at the CNRS, quoted by 'Geo', who sees in these phenomena "extremely strong anomalies, quite striking and worrying".

So what is going on? Well, the oceans absorb 90% of the heat generated by the greenhouse effect. Such heat waves are therefore logical in a period of global warming.

Other explanations have been put forward by scientists, such as the reduction of Saharan dust carried by the wind, which normally has a cooling effect on the atmosphere.

The drop in sulfur emissions from boats, another usual cooling factor, has also been mentioned to explain the current heat waves. But these are just guesses at this point.

On the other hand, it is still too early to see the consequences of the El Niño climatic phenomenon: experts expect more of an impact in the spring of 2024.

Be that as it may, these heat waves have a devastating effect on biodiversity. Scientists expect massive excess mortality of marine species, especially corals and invertebrates.

In addition, these high temperatures slow down the growth of phytoplankton, which has cascading effects on the food chain of which these microorganisms are the basis. Enough to starve crustaceans as well as fish and birds.

The warming of the oceans could also accelerate the migration of certain species towards the poles where the waters are colder. There will therefore be fewer fish in the area between the tropics.

In addition, heat waves at sea have the effect of bleaching coral reefs, precious barriers for the preservation of the environment.

Caused by global warming, sea heat waves also have an amplifying effect: by warming up, the ocean could in fact absorb a smaller part of the CO2 emitted by humans, which would once again increase the temperature of the atmosphere.

In 2022, the Mediterranean Sea was affected by intense heat. Almost all of its western part had experienced a heat wave in late spring.

In the Mediterranean as elsewhere, the evolution of these heat episodes is worrying for the future. As noted by the French Center for Scientific Research, "a significant increase in the duration, spatial extension and intensity of surface ocean heat waves" has been observed in recent decades.

And the worst may be ahead of us: according to Samuel Somot, researcher at the National Center for Meteorological Research (CNRM), quoted by 'L'Obs', these heat waves "could last four months, with significant temperature anomalies on the whole sea up to four times more intense".

For Robert Schlegel, researcher at the Institut de la Mer de Villefranche (IMEV), quoted by the 'HuffPost', "the entire world ocean will be close to a state of almost constant marine heat wave" by 2050.

Less visible than damage on land such as heat waves or fires, heat waves at sea are no less worrying. To preserve temperatures and biodiversity, the solution involves drastically limiting global warming.