Yellow Submarine Finds River at the Bottom of the Sea
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LONDON (Aug. 2) -- It sounds like the plot of a forgotten Beatles movie: A team of scientists sends a yellow submarine to the bottom of the sea and finds a meandering underwater river -- complete with waterfalls and rapids -- flowing along the ocean floor.
That may seem far-out, but it's exactly what a group of researchers from England's University of Leeds, Canada's Memorial University and Turkey's Institute of Marine Science discovered when they carried out a detailed study of a puzzling 37-mile-long channel at the bottom of the Black Sea.
The existence of these underwater rivers -- or submarine channels -- has been suspected since the 1970s, when advances in sonar technology allowed scientists to produce detailed 3-D maps of the ocean floor. Unlike ocean trenches, which are geological formations made by the movements of tectonic plates, submarine channels are created when water loaded with salt or sediment washes along and erodes the seabed. Until now, though, exactly how this dense water moves along these channels has been something of a mystery.
Rick Hiscott and Ali Aksu from Memorial University
An infrared image shows a 37-mile-long channel at the bottom of the Black Sea.
To find out more about what's going on under the waves, Dan Parsons, a research fellow at Leeds' School of Earth and Environment, and his international colleagues sent a (bright yellow) robot sub down to the bottom of the Black Sea to carry out the first in-depth examination of a submarine channel. Equipped with an underwater speed camera, a gadget that measures water density and a sonar system, the sub examined the workings of the river, which is 3,170 feet wide in places and has banks up to 82 feet high. The research will be published in an upcoming issue of the journal Geology.
The scientists found that the channel is filled with fast-moving salty water spilling from the Mediterranean into the less salty Black Sea at the two bodies' meeting point: the Bosphorus Strait. "The Mediterranean-derived water flows as a result of gravity, acting on the density difference that's produced by higher concentrations of salt," Parsons told AOL News. "It's essentially the same process that takes place when you pour bubble bath into water and it sinks and flows along the bottom of the tub toward the plug hole."
Except the Black Sea is a very big bathtub: Some 22,000 cubic meters of water pass through the submarine channel every second. That's 350 times more than the flow of England's Thames, or roughly that of the Missouri River where it flows into the Mississippi. This torrent moves along at around four miles per hour for some 37 miles, then it hits the edge of the sea shelf and dissipates into the depths.
Parsons says that this channel -- which, if located on land, would be the world's sixth largest river based on the amount of water flowing through it -- would likely have started to form at the end of the last ice age some 8,000 years ago. As melting glaciers pushed global sea levels close to their current high point, the Mediterranean would have breached through the Bosphorus -- then a thin strip of dry land -- and splashed into the Black Sea. (Which at the time was just an isolated freshwater lake.)
Much larger submarine channels exist elsewhere in the world wherever great rivers flow into the sea. Close to the spot where the Amazon opens into the Atlantic, for example, you'll find a 2,500-mile riverbed that used to carry nutrient-rich sediment out to the barren abyssal plain. But Parsons notes that dense water stopped flowing along those channels when "sea levels came up after the end of the last ice age and the mouths of rivers like the Amazon moved away from the continental shelf. So there's now a disconnect between where the river mouth is and the start of the submarine channel."
By studying the much smaller Black Sea channel -- the last known active undersea river -- Parsons and his colleagues have been able to find out how these dead (or perhaps just resting) rivers formed and distributed sediment across the underwater flood plain.
"Many people have previously assumed that this process works just like it does on land," says Parsons. "But it doesn't. When water on land moves around a river bend, we see that it has a corkscrew flow to it. That's because the water near the surface faces less resistance and so travels in a straight line that causes it to collide with the riverbank. Water closer to the bed, though, moves slower and turns more with the winding river path."
But at the bottom of the sea, where density drives movement, water spirals in the opposite direction -- meaning the heavier H2O at the bottom of the channel travels faster and crashes into bends, while the stuff on top weaves with the river. That leads to sediment being laid down in a radically different pattern to what happens up here on drier ground.
This greater understanding of underwater flows, and how detritus layers up over the centuries, is certain to help oil and gas firms hunting for hydrocarbons under dead submarine channels. Because by being able to better predict what sub-sea strata they're likely to encounter, the firms will be able to locate the easiest spot to drill -- an important bit of knowledge, as individual wells can cost more than $100 million.
LONDON (Aug. 2) -- It sounds like the plot of a forgotten Beatles movie: A team of scientists sends a yellow submarine to the bottom of the sea and finds a meandering underwater river -- complete with waterfalls and rapids -- flowing along the ocean floor.
That may seem far-out, but it's exactly what a group of researchers from England's University of Leeds, Canada's Memorial University and Turkey's Institute of Marine Science discovered when they carried out a detailed study of a puzzling 37-mile-long channel at the bottom of the Black Sea.
The existence of these underwater rivers -- or submarine channels -- has been suspected since the 1970s, when advances in sonar technology allowed scientists to produce detailed 3-D maps of the ocean floor. Unlike ocean trenches, which are geological formations made by the movements of tectonic plates, submarine channels are created when water loaded with salt or sediment washes along and erodes the seabed. Until now, though, exactly how this dense water moves along these channels has been something of a mystery.
Rick Hiscott and Ali Aksu from Memorial University
An infrared image shows a 37-mile-long channel at the bottom of the Black Sea.
To find out more about what's going on under the waves, Dan Parsons, a research fellow at Leeds' School of Earth and Environment, and his international colleagues sent a (bright yellow) robot sub down to the bottom of the Black Sea to carry out the first in-depth examination of a submarine channel. Equipped with an underwater speed camera, a gadget that measures water density and a sonar system, the sub examined the workings of the river, which is 3,170 feet wide in places and has banks up to 82 feet high. The research will be published in an upcoming issue of the journal Geology.
The scientists found that the channel is filled with fast-moving salty water spilling from the Mediterranean into the less salty Black Sea at the two bodies' meeting point: the Bosphorus Strait. "The Mediterranean-derived water flows as a result of gravity, acting on the density difference that's produced by higher concentrations of salt," Parsons told AOL News. "It's essentially the same process that takes place when you pour bubble bath into water and it sinks and flows along the bottom of the tub toward the plug hole."
Except the Black Sea is a very big bathtub: Some 22,000 cubic meters of water pass through the submarine channel every second. That's 350 times more than the flow of England's Thames, or roughly that of the Missouri River where it flows into the Mississippi. This torrent moves along at around four miles per hour for some 37 miles, then it hits the edge of the sea shelf and dissipates into the depths.
Parsons says that this channel -- which, if located on land, would be the world's sixth largest river based on the amount of water flowing through it -- would likely have started to form at the end of the last ice age some 8,000 years ago. As melting glaciers pushed global sea levels close to their current high point, the Mediterranean would have breached through the Bosphorus -- then a thin strip of dry land -- and splashed into the Black Sea. (Which at the time was just an isolated freshwater lake.)
Much larger submarine channels exist elsewhere in the world wherever great rivers flow into the sea. Close to the spot where the Amazon opens into the Atlantic, for example, you'll find a 2,500-mile riverbed that used to carry nutrient-rich sediment out to the barren abyssal plain. But Parsons notes that dense water stopped flowing along those channels when "sea levels came up after the end of the last ice age and the mouths of rivers like the Amazon moved away from the continental shelf. So there's now a disconnect between where the river mouth is and the start of the submarine channel."
By studying the much smaller Black Sea channel -- the last known active undersea river -- Parsons and his colleagues have been able to find out how these dead (or perhaps just resting) rivers formed and distributed sediment across the underwater flood plain.
"Many people have previously assumed that this process works just like it does on land," says Parsons. "But it doesn't. When water on land moves around a river bend, we see that it has a corkscrew flow to it. That's because the water near the surface faces less resistance and so travels in a straight line that causes it to collide with the riverbank. Water closer to the bed, though, moves slower and turns more with the winding river path."
But at the bottom of the sea, where density drives movement, water spirals in the opposite direction -- meaning the heavier H2O at the bottom of the channel travels faster and crashes into bends, while the stuff on top weaves with the river. That leads to sediment being laid down in a radically different pattern to what happens up here on drier ground.
This greater understanding of underwater flows, and how detritus layers up over the centuries, is certain to help oil and gas firms hunting for hydrocarbons under dead submarine channels. Because by being able to better predict what sub-sea strata they're likely to encounter, the firms will be able to locate the easiest spot to drill -- an important bit of knowledge, as individual wells can cost more than $100 million.