Oct 3, 2020 11:49 PM
Dead water comes alive
https://www.hakaimagazine.com/news/dead-...mes-alive/
EXCERPTS: Norwegian mariners called it dødvann -- dead water. They’d known for centuries that patches of seawater in narrow fjords could mysteriously sap a ship’s speed, drastically slowing it or stopping it altogether. In his 1897 book, Farthest North, explorer Fridtjof Nansen wrote of his encounter with dead water north of Siberia in 1893 [...] Nansen’s report of dead water was investigated by scientists at the time, including the Swedish oceanographer Vagn Walfrid Ekman. In 1904, Ekman published research that showed dead water was caused by hidden waves in a dense subsurface layer of salt water that slowed the forward motion of a ship. Today’s speedy ships easily overcome these submerged waves, and for most mariners dead water is now largely forgotten.
But more than 100 years later, scientists are still exploring the phenomenon, and a new investigation has uncovered more details about its underlying mechanics. [...] In their experiments, the scientists dragged scale models of boats at different speeds through tanks containing fresh water lying on top of salt water, assessing how the boats’ passage affected the surface and underwater layers. They found that the two different phenomena -- the drag of dead water described by Nansen, and the surges in speed described by Ekman -- are both caused by waves in the hidden saltwater layer. In particular, the Ekman effect occurs when the subsurface waves bounce off the sides of a laboratory tank and create an oscillation in the surface speed of a vessel. Rousseaux says the Ekman effect could make it difficult for slower ships trying to navigate narrow passages, such as fjords and sea locks.
The new study also suggests other consequences of dead water. Leo Maas [...] says that although the effects of these subsurface waves are negligible for most motor-driven boats today, they could still affect swimmers, since their hands often interact with deeper layers of water. He points out that stratification in salt and fresh water can result from differences in water temperature, particularly in hot and calm weather. “This effect might play a role in tragic fair-weather drownings,” he says... (MORE - details)
Water, Water, Every Where — And Now Scientists Know Where It Came From
https://www.npr.org/2020/08/27/906654225...-came-from
INTRO: Water on Earth is omnipresent and essential for life as we know it, and yet scientists remain a bit baffled about where all of this water came from: Was it present when the planet formed, or did the planet form dry and only later get its water from impacts with water-rich objects such as comets? A new study in the journal Science suggests that the Earth likely got a lot of its precious water from the original materials that built the planet, instead of having water arrive later from afar... (MORE)
https://www.hakaimagazine.com/news/dead-...mes-alive/
EXCERPTS: Norwegian mariners called it dødvann -- dead water. They’d known for centuries that patches of seawater in narrow fjords could mysteriously sap a ship’s speed, drastically slowing it or stopping it altogether. In his 1897 book, Farthest North, explorer Fridtjof Nansen wrote of his encounter with dead water north of Siberia in 1893 [...] Nansen’s report of dead water was investigated by scientists at the time, including the Swedish oceanographer Vagn Walfrid Ekman. In 1904, Ekman published research that showed dead water was caused by hidden waves in a dense subsurface layer of salt water that slowed the forward motion of a ship. Today’s speedy ships easily overcome these submerged waves, and for most mariners dead water is now largely forgotten.
But more than 100 years later, scientists are still exploring the phenomenon, and a new investigation has uncovered more details about its underlying mechanics. [...] In their experiments, the scientists dragged scale models of boats at different speeds through tanks containing fresh water lying on top of salt water, assessing how the boats’ passage affected the surface and underwater layers. They found that the two different phenomena -- the drag of dead water described by Nansen, and the surges in speed described by Ekman -- are both caused by waves in the hidden saltwater layer. In particular, the Ekman effect occurs when the subsurface waves bounce off the sides of a laboratory tank and create an oscillation in the surface speed of a vessel. Rousseaux says the Ekman effect could make it difficult for slower ships trying to navigate narrow passages, such as fjords and sea locks.
The new study also suggests other consequences of dead water. Leo Maas [...] says that although the effects of these subsurface waves are negligible for most motor-driven boats today, they could still affect swimmers, since their hands often interact with deeper layers of water. He points out that stratification in salt and fresh water can result from differences in water temperature, particularly in hot and calm weather. “This effect might play a role in tragic fair-weather drownings,” he says... (MORE - details)
Water, Water, Every Where — And Now Scientists Know Where It Came From
https://www.npr.org/2020/08/27/906654225...-came-from
INTRO: Water on Earth is omnipresent and essential for life as we know it, and yet scientists remain a bit baffled about where all of this water came from: Was it present when the planet formed, or did the planet form dry and only later get its water from impacts with water-rich objects such as comets? A new study in the journal Science suggests that the Earth likely got a lot of its precious water from the original materials that built the planet, instead of having water arrive later from afar... (MORE)