What is “dead water”, the phenomenon that traps ships in the middle of the ocean (and how scientists solved this mystery from a century ago)


In 1893, the Norwegian explorer Fridtjof Nansen began an expedition to the North Pole that would give him world fame for breaking the record for northern latitude.

That journey would also make him the first person to observe a strange phenomenon that has puzzled oceanographers for more than a century.

While sailing through the Arctic waters of northern Siberia, Nansen noticed that his ship, the Fram, suddenly began to stop, even though its engines were running at full throttle.

The adventurer would describe the anomaly as a “mysterious force” holding his boat back, making it almost impossible to maneuver.

“We made loops in our course, sometimes we wandered around, we tried all kinds of strategies to avoid it, but with very little success,” he later recounted.

Nansen thus became the first to observe this phenomenon, which he gave the name of “dead water”.


Eleven years later, in 1904, the Swedish physicist and oceanographer Vagn Walfrid Ekman managed to identify what caused this anomaly.

Ekman demonstrated in a laboratory that waves formed in this part of the Arctic Ocean below the surface, between layers of salt and fresh water – which have different densities – interacted with a ship, generating resistance.

In the Arctic water layers of different salinity are mixed.

He attributed it to melting glaciers, forming a layer of fresh water over the sea, more salty and dense.

However, in his laboratory tests, Ekman saw that the drag waves generated oscillations in the speed of the ship.

This differed from the observations of Nansen, whose ship stopped at a constant and abnormally low speed.

Until now, no one has been able to explain these differences, nor understand exactly how the effect of dead water works.

But an interdisciplinary team from the National Center for Scientific Research (CNRS), the most important research institution in France, and from the University of Poitiers, he believes he has revealed both mysteries.

“Conveyer belt”

The group of physicists, experts in fluid mechanics and French mathematicians used a mathematical classification of different internal waves and an analysis of experimental images at sub-pixel scale to study the phenomenon.

In a paper published in the scientific journal PNAS in early July, they concluded that the speed variations described by Ekman are due to the generation of waves that act as a kind of “undulating conveyor belt”.

Dead water traps ships and makes them move back and forth, like they’re on an undulating conveyor belt, French scientists discovered.

This “tape” causes boats to move back and forth.

The scientists also managed to unify Ekman’s observations with Nansen’s, claiming that the oscillating effect is only temporary.

Finally “the ship ends up escaping and reaches the constant speed that Nansen described“they published in their study.

The experts highlighted that the phenomenon does not only occur in places with glaciers, but in all seas and oceans where waters of different densities mix.

“It is also found in cold mountain lakes in summer because there is temperature stratification, and therefore there is a risk that swimmers will drown,” study co-author Germain Rousseaux said in statements to Spain’s ABC newspaper.

Rousseaux added that the phenomenon also occurs at the mouth of rivers such as the Orinoco, in South America, due to the flow of rivers with sediments on salty sea water.


Interestingly, this study was done not to unravel the mystery of what happened to Nansen over a century ago, but to unravel a much older unknown.

Was Cleopatra and Marco Antonio’s fleet trapped in dead water during the Battle of Accio?

The work is part of a large project that investigates why during the Battle of Action o actium (in 31 BC), in ancient Greece, the great ships of Cleopatra and Marco Antonio lost when they faced the weaker ships of César Octavio.

Could Accio Bay, which has all the characteristics of a fjord, have trapped the Queen of Egypt’s fleet in dead water?

That was actually what the French scientists asked themselves.

“Now we have another hypothesis to explain this resounding defeat, which in ancient times was attributed to remoras, ‘sucker fish’ attached to hooves, according to legend.”

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