September 9, 2013
Skyscraper-Size Waves Circulate Energy, Nutrients In Deep Ocean
Brett Smith for redOrbit.com - Your Universe Online
While massive waves are a surfer’s dream, they are also fascinating to oceanographers – particularly those waves breaking deep in the ocean.
“Climate models are really sensitive not only to how much turbulence there is in the deep ocean, but to where it is,” said study author Matthew Alford, an oceanographer in the UW Applied Physics Laboratory. “The primary importance of understanding deep-ocean turbulence is to get the climate models right on long timescales.”
For the study, which was published in Geophysical Research Letters, the UW researchers were particularly interested in the Samoan Passage, a narrow channel deep in the South Pacific that funnels cold water flowing from Antarctica. This cold, dense Antarctic melt water sinks deep into the Pacific, eventually coursing through a 25-mile gap in the ocean floor northeast of Samoa.
“Basically the entire South Pacific flow is blocked by this huge submarine ridge,” Alford said. “The amount of water that’s trying to get northward through this gap is just tremendous – 6 million cubic meters of water per second, or about 35 Amazon Rivers.”
Previous studies have measured currents through the Samoan Passage, but weren’t able to determine their scale because of technical challenges.
In 2012, the UW oceanographer took a seven-week cruise across the South Pacific to track the 800-foot-high waves flowing 3 miles below the ocean’s surface. After taking an hour-and-a-half to lower instruments to the seafloor, the team’s scientific vessel traveled at only a half knot, slower than normal walking speed, during 30-hour periods. New technologies allowed the scientists to record the turbulence directly and take measurements from instruments lowered over 3 miles off the side of the ship.
The team’s measurements illustrated how these giant waves break and provide mixing 1,000 to 10,000 times that of the surrounding water.
“Oceanographers used to talk about the so-called ‘dark mixing’ problem, where they knew that there should be a certain amount of turbulence in the deep ocean, and yet every time they made a measurement they observed a tenth of that,” Alford said. “We found there’s loads and loads of turbulence in the Samoan Passage, and detailed measurements show it’s due to breaking waves.”
The research team said the Samoan Passage is important because of the volume of water it mixes, but similar and just as important processes transfer heat, energy and nutrients in other places deep in the ocean. Better models of deep-ocean mixing could help in creating simulations of global currents and help determine where to place instruments to track ocean phenomenon.
The team said they left instruments along the Samoan Passage to record long-term measurements. They are currently planning another 40-day cruise in January to collect these instruments and track localized currents flowing through the deep-sea channel.
Although the deep sea waves are massive, Alford half-jokingly said surfers wouldn’t have any fun riding them.
“It would be really boring,” said Alford, a surfer himself. “The waves can take an hour to break, and I think most surfers are not going to wait that long for one wave.”
Image Below: The deep-sea waves are 800 feet tall, as high as a skyscraper. Credit: Tom Peacock, MIT | Wide Eye Productions