What is the Dead Sea? - many people know. And what is the phenomenon of "dead water" and is it related to the first concept? French scientists have clarified this matter
Back in 1893, the famous Norwegian traveler Fridtjof Nansen was sailing in the Arctic waters with a team on the schooner "Fram", when the sailors suddenly noticed a very strange phenomenon.
Some unknown force seemed to be holding the "Fram", Nansen later wrote in his diaries. At the same time, the schooner did not always obey the helm. The crew forced the ship to dodge, turn around, embark on other evasions just to get rid of the "brake", but all attempts failed.
It was then that Nansen dubbed the emerging phenomenon "dead water". Due to its effects, the Fram has lost three-quarters of its normal move.
According to the Internet edition NewScientist, a group of French researchers reproduced in a laboratory a scheme of action of a similar phenomenon, the essence of which is the interaction of two or more layers of water with different levels of salinity and, as a result, density. Such phenomena can occur with melting glaciers, when lighter fresh water covers a layer of denser sea salt water.
Waves arising in the hidden layer can slow down the movement of the vessel, which is not visible to the eye of the observer.
The current experiment, carried out by French scientists and filmed by them on video, will help the scientific community not only better understand the phenomenon of "dead water", but also the behavior of marine areas prone to such delamination.
Researchers from the University of Lyon have discovered a hidden wave at the junction of water layers, which literally pursues and slows down the movement of the vessel. They carried out this experiment in a laboratory 3-meter bath filled with water, through which a toy boat was pulled on a cord.
Promotional video:
The layers of water, divided by the level of salinity, and hence density, were colored in different colors.
Before their eyes, the same thing was happening as the witnesses described the phenomenon in real conditions in the open sea: although the water surface remained absolutely calm, the boat unexpectedly slowed down as it came into contact with a hidden wave.
In a similar situation, a zone of low pressure (depression) arises under the bottom of the vessel, which impedes its progress, explained researcher Mathieu Mercier.
It happens that the ship itself creates this wave - water from the lower layers is drawn upward into the zone of its movement. As a consequence, an oscillation occurs at the boundary between the layers, which gradually increases in the direction of the vessel's movement.
The wave increases, just as its speed increases, until the moment when the wave itself and the cavity formed in front of it do not catch up with the ship, aligning with it and absorbing its energy. Then the wave breaks against the side.
Earlier research in this area has studied only two layers of water, whereas in reality ocean water is divided into many layers with slightly different salinity levels.
When the scientists introduced the third layer into the experiment, hidden waves appeared at all boundaries separating them, slowing down the movement of the ship equally.
Further study of the ways in which such "interlayer waves" originate and propagate, it is believed, could help scientists understand the dynamics of exchange taking place in the oceans - how, for example, pollutants mix and how they percolate, reaching the depths of the ocean.
The effect of "dead water", according to scientists, can also explain why highly trained swimmers have unexpected difficulties when swimming in the ocean.
