The slowdown of the gulf Stream?

The two arctic engines driving the Gulf Stream are showing signs of weakness.

A heating failure in Europe is therefore becoming clearer, despite global warming.

"The chimneys have almost all disappeared!" With the face of an old sea bass, Peter Wadhams certainly had to face some serious issues during his life as an oceanographer. But this time, in front of the journalists who came to attend the European Symposium of Earth Sciences in Vienna, he gives the impression of returning from a meeting with the devil. Indeed, the account of his last submarine expedition under the Odden sea ice in the Labrador Sea is worrying.

“Until recently, we could observe a dozen giant chimneys made up of columns of cold, dense water flowing from the surface to the bottom, 3 meters below. But now there are only two of weak constitution left. "

If the boss of an important laboratory at the University of Cambridge, medalist by the queen herself, loses his British phlegm, it is because he observed the first serious failure of the Gulf Stream. However, everyone knows that the disappearance of this warm Atlantic current would also condemn the dry English and Scandinavians to exchange their car for a snow scooter and the French to put on a down jacket all winter. For sure, imagining Elisabeth II saluting from a royal sleigh is enough to freak out a subject of Her Majesty.

The Gulf Stream is the emerged part of an immense conveyor belt - the thermohaline circulation - circling the oceanic world (170 times the Amazon!). Having heated its waters in the tropical sun, it sets course for Florida then bounces towards Europe before turning north, dividing into two branches framing Greenland. Along the way, the water becomes loaded with salt due to evaporation, then cools on contact with arctic breath. So it becomes more and more dense, more and more heavy. Under the pack ice, it still swallows up the salt expelled by the ice crystals in formation. It is the drop that breaks the camel's back, it plunges into the abyss and thus constitutes the motor of the conveyor belt. The submerged water flows south, as far as Antarctica, passes into the Pacific. It reappears in the open air, then plunges again and, finally, resurfaces to go up the Atlantic. The merry-go-round is thus completed in a thousand years!

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So much so that the water bathing Scandinavia today is the one that accompanied the Vikings in their discovery of America around the year 1000.

The poor draft of the chimneys under the Odden would be a heavy blow to global warming. It would result from the least formation of pack ice in winter, the melting of Greenland rejecting more fresh water and the increase in the temperature of arctic waters.

"However, we should not draw apocalyptic conclusions, tries to reassure Marie-Noëlle Houssais, oceanographer at the CNRS ocean laboratory. To be concerned, the disappearance of the chimneys would have to be truly permanent and that it should take place elsewhere than under the Odden. "

The problem is that the main engine of the Gulf Stream, in the Norwegian Sea, also admits a small weakness. Its flow has slowed by 2 to 4% per year for ten years. This time, the main responsible for this failure would be the Siberian rivers! Indeed, global warming is raining more in Siberia; however, this one rejects the majority of its fresh water in the Arctic by six giant rivers.

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In 2002, Bruce J. Peterson, of the Woods Hole (Massachusetts) marine biology laboratory, revealed that the global flow of these rivers had increased by 7% between 1936 and 1999. That is 128 cubic kilometers of additional fresh water per year, thus lightening by dilution of salt the waters of the Arctic. A global warming of 5,8 ° C by 2100 would increase the annual score by 1 cubic kilometers.

Much more than it takes to stop the Gulf Stream.

Too many mysteries. But, after all, it won't be his first failure. The study of ice cores reveals several decommissioning, the last of which was only ten thousand years old. When will this happen again? In five years ? ten years ? fifty years ? The planet's ocean and climate workings hold too many mysteries for scientists to provide a precise date. So they still do not know the role played by two monstrous bubbles of fresh water (58 cubic kilometers in total, or two and a half times the sea ice) which are hidden in the liquid bowels of the Arctic. It would be enough that 000% of this underwater lake escapes for the engine of the Gulf Stream to experience serious failures.

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Much nonsense has been written about the future of Western Europe without its ocean heater. Let lovers of seal hunting be disappointed, France will not become Siberia. "Its climate will rather resemble that of the east coast of the United States, which is not bathed by a hot current like the Gulf Stream," we told Météo France.

If there is no fear of a new ice age, it is because the planet is heating up. The simulations predict a drop in temperature of 5 ° C in Scandinavia and Great Britain, and "only" 2 ° C over most of France. Other consequences are also to be feared: an immediate rise in the level of the North Atlantic by 1 meter, according to the Potsdam Institute. But also a scarcity of fish, because the thermohaline circulation tears from the sea floor the mineral salts necessary for the plankton to flourish at the origin of the oceanic food chain.

Soon, His Majesty's intrepid sailor, Peter Wadhams, will embark on a new cruise under the Arctic sea ice. Will he find his precious fireplaces? We must hope so, otherwise the bad news will cast a great chill.

by Frederic Lewino for LePoint.fr

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