An “invisible massacre” that kills marine creatures in the Atlantic Ocean

Despite its relatively limited size compared to the fires in Canada, the unprecedented heat wave currently hitting the waters of the Atlantic Ocean would, according to scientists, cause an invisible massacre of marine species, in a sound phenomenon that may recur with the exacerbation of climate warming.

Between March and May, the average ocean surface temperature reached an all-time high since measurements began 174 years ago, outstripping the 20th-century average by 0.83 degrees Celsius, according to NOAA data.

This marine heat wave did not escape the Atlantic Ocean, which in June suffered from heat waves that were especially severe from southern Iceland to Africa, with temperature differences of more than 5 degrees Celsius off the British Isles.

“unprecedented” situation

“Such temperature differences in this part of the North Atlantic are unprecedented,” said Daniela Schmidt, professor of earth sciences at the University of Bristol, in remarks reported by the British Science Media Centre.

The oceanographer and climatologist at the National Center for Scientific Research in France, Jean-Baptiste Salet, confirms the existence of “very strong, striking and very disturbing imbalances.”

This marine heat wave, with temperatures exceeding 23°C in the North Atlantic, doesn’t exactly surprise scientists who know that oceans absorb 90% of the heat generated by climate warming. Therefore, this type of event will become more frequent and intense under the influence of climate warming.

As Jean-Pierre Gattuso, director of research at the National Center for Scientific Research, co-author of a report for the Intergovernmental Panel on Climate Change (UN climate experts), notes, “It is surprising that things are moving so quickly.”

Many hypotheses have been put forward to explain this extreme phenomenon, including the shrinkage of wind-borne desert dust or sulfur emissions from ships, two types of aerosols that usually have a cooling effect on the atmosphere.

But it “remains just hypotheses,” Saleh estimates.

As for the “El Niño” phenomenon, it seems that it has not developed to a large extent, meaning that it has no effect on the North Atlantic. “We expect an impact next spring,” explains Juliette Mineo, an oceanographer at the Research Institute for Development.

The researcher expects a “possible modification of sea currents,” or an atmospheric phenomenon that may intersect with climate warming.

Marine Life – iStock

“turning point”

Regardless of the origin of this ocean heat wave, scientists expect it to cause a “mass die-off” of marine species, including corals and invertebrates. “But since it’s happening below the surface of the ocean, it will pass unnoticed,” says Schmidt.

During heat waves in the Mediterranean, about fifty species (including corals, sea urchins, molluscs, and Posidonia) were affected by “a huge wave of death between the surface and a depth of 45 meters,” according to Gattuso.

Other species prefer to migrate towards the poles. According to the researcher, “the waters of Norway and Iceland, for example, will become richer in fish,” at the expense of the countries of the tropical region.

By warming, the ocean, which captures a quarter of the carbon dioxide emissions left behind by humans, could eventually lose part of its role as a carbon pump. Then this will have an “amplifying effect on atmospheric warming,” Mineo asserts, speaking of a “turning point” in this path, after which it will not be the same.

“These tipping points, we know they exist, but it’s hard to know the level of warming that caused them,” Salet says.

By the end of the century, the Intergovernmental Panel on Climate Change projects a 50-fold increase in the frequency of ocean heat waves in its most pessimistic scenario, with episodes that will be ten times as intense.

But Gattuso reassures that “we can limit the damage”. “If greenhouse gas emissions follow a path consistent with the Paris Agreement, we can completely stop ocean warming and acidification,” he asserts, as “all is not lost.”