The Mediterranean is overheating

The Mediterranean Sea has been overheating for a few weeks. Sea surface temperatures are reaching exceptional levels, 4 to 5°C above normal. Experts are concerned about the possible repercussions of this phenomenon on marine life… and human life.

Posted at 6:00 a.m.

Audrey Pilon Topkara

Audrey Pilon Topkara The Press

"From the Balearic Sea to Sardinia, as well as to the east of Corsica and throughout the Tyrrhenian Sea, exceptional surface temperatures are observed between 28 and 30°C", reports Mercator International Ocean.

This non-profit organization based in Toulouse brings together the main oceanographic institutes of France, Italy, Spain, Great Britain and Norway and directs the European ocean monitoring service, the Copernicus Marine Monitoring Service (CMEMS). .

These temperature values ​​are abnormally hot, since they exceed the average values ​​in the season by 4 to 5 ° C, underlines the organization.


Mercator Océan International is observing temperatures 4 to 5 degrees above seasonal averages, particularly off the French and Italian coasts.

A conducive context

“The sea heat wave began around mid-May in the Ligurian Sea – between Italy and northern Corsica – then continued in June in the Gulf of Taranto, in southeastern Italy” , says Karina von Schuckmann, oceanographer at Mercator Ocean International, in an interview with The Press.

“It is true that there are ocean regions that reach 30°C, but this had never happened in the Mediterranean. We are therefore experiencing an exceptional phenomenon”, underlines Jean-Pierre Gattuso, research director of the National Center for Meteorological Research (CNRM) at the Oceanography Laboratory in Villefranche-sur-Mer, a French town near Nice.

The particularly high land temperatures in southern Europe in recent weeks combined with the absence of wind have caused the water temperature to rise, explains the researcher.

When there is a gale, the surface seawater, which is warm, mixes with deep seawater, which is much colder. So that tempers it all.

Jean-Pierre Gattuso, research director of the National Center for Meteorological Research

Mr. Gattuso points out that the current marine heatwave exceeds the temperature records set during the European heatwave of 2003, a major climatic event that occurred from June to August marked by many temperature records.

“In August 2003, it was a very intense sea and land heat wave. In the south of France, there were 10,000 excess deaths,” recalls the researcher.

Upheavals for marine life

The increase in the frequency and intensity of sea heat waves could cause the disappearance of several marine species.

A recent study by the Institut de Ciències del Mar (Institute of Marine Sciences) in Barcelona reveals that between 2015 and 2019, 90% of the Mediterranean was affected at one time or another by one or more sea heat waves. . Each resulted in massive mortalities in some fifty species of plants and animals.

  • Gorgon, species of coral affected by the sea heat wave


    Gorgon, species of coral affected by the sea heat wave

  • Gorgon, species of coral


    Gorgon, species of coral


“Among the species affected are the gorgonians [espèce de corail], corals, sea urchins, lists Jean-Pierre Gattuso, co-author of the study. There is an emblematic plant, Posidonia, which cannot stand these increasingly extreme temperatures. Spanish colleagues estimate that it could disappear from the Balearic Islands by 2040.”

Posidonia is a marine plant that absorbs CO2 and stores it in underwater sediments. It protects the shoreline from erosion and also serves as a breeding ground for several marine species.

The increase in water temperature also leads to the movement of species. Although many of them are not harmful, others pose a problem by disrupting biodiversity.

About 400 species from the Red Sea managed to enter the Mediterranean through the Suez Canal.

Jean-Pierre Gattuso, research director of the National Center for Meteorological Research

“This is the case of the rabbitfish, a voracious herbivore that eats algae and competes with native fish. There's the lionfish, whose dorsal fin rays sting and are poisonous,” says Gattuso.

Effects for humans

"Another consequence of these extreme temperatures, and which is specific to our region, are the Mediterranean episodes", adds Jean-Pierre Gattuso.

Mediterranean episodes are linked to upwellings of hot, humid and unstable air from the Mediterranean which can cause violent thunderstorms and heavy rainfall. They usually occur in autumn, when the sea is warmest, which promotes strong evaporation.

"The damage is sometimes extremely violent: houses, bridges and roads that are washed away, overflowing rivers, floods", illustrates the researcher.

For Karina von Schuckmann, it is imperative to reach the targets set by the Paris agreement if we want to avoid disastrous consequences. “The solutions are known and within reach. The oceans already absorb 90% of Earth's heat, so it's important not to get to the tipping point,” she insists.

There is no doubt in the eyes of the two experts that we can associate this sea heatwave with climate change.

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