Understanding the sea is to understand our planet better, at a fundamental level. Even the very contours of this world are still unmapped: We probably know more about the surface of Mars than we know about the ocean floor. Their behaviors and adaptations remain inexplicable. Many of its creatures are still unknown to us - both in kind and number. The ocean, in this light, is like an alien world within our own. The research was funded by the National Science Foundation.The Earth is mainly a water world - more than 70 percent of its surface is covered by oceans - and yet we know so little about what resides beneath the waves. The team will do another 40-day cruise in January to collect those instruments and map currents flowing through various gaps in the intricate channel.Ĭo-authors of the paper are James Girton, Gunnar Voet and John Mickett at the UW Applied Physics Lab Glenn Carter at the University of Hawaii and Jody Klymak at the University of Victoria. The researchers left instruments recording long-term measurements. New technology let the scientists measure turbulence directly and make measurements from instruments lowered more than 3 miles off the side of the ship. Instruments took 1.5 hours to lower to the seafloor, and the ship traveled at only a half knot, slower than a person walking, during the 30-hour casts. In fact, even making the measurements was painstaking work. “The waves can take an hour to break, and I think most surfers are not going to wait that long for one wave.” “It would be really boring,” admitted Alford, who is a surfer. Researchers lower an instrument off the back of the ship. On a lighter note: Could an intrepid surfer ride these killer deep-sea waves? Better knowledge of deep-ocean mixing could help simulate global currents and place instruments to track any changes. The Samoan Passage is important because it mixes so much water, but similar processes happen in other places, Alford said. This mixing helps explain why dense, cold water doesn’t permanently pool at the bottom of the ocean and instead rises as part of a global conveyor-belt circulation pattern. Thus the deepest water, the densest in the world, mixes with upper layers and disappears. These waves become unstable and turbulent, and break. It turns out layers of water flowing over two consecutive ridges form a lee wave, like those in air that passes over mountains. “We found there’s loads and loads of turbulence in the Samoan Passage, and detailed measurements show it’s due to breaking waves.” “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. Their measurements show these giant waves do break, producing mixing 1,000 to 10,000 times that of the surrounding slow-moving water. In the summer of 2012 the UW team embarked on a seven-week cruise to track the 800-foot-high waves that form atop the flow, 3 miles below the ocean’s surface. The deep-sea waves are 800 feet tall, as high as a skyscraper. The scientists inferred that a lot of mixing must also happen there, but couldn’t measure it. In the 1990s, a major expedition measured these currents through the Samoan Passage. “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.” “Basically the entire South Pacific flow is blocked by this huge submarine ridge,” Alford said. “The primary importance of understanding deep-ocean turbulence is to get the climate models right on long timescales,” Alford said.ĭense water in Antarctica sinks to the deep Pacific, where it eventually surges through a 25-mile gap in the submarine landscape northeast of Samoa. He led the expedition to the Samoan Passage, a narrow channel in the South Pacific Ocean that funnels water flowing from Antarctica. “Climate models are really sensitive not only to how much turbulence there is in the deep ocean, but to where it is,” said lead author Matthew Alford, an oceanographer in the UW Applied Physics Laboratory. Where and how they break is important for the planet’s climate. These skyscraper-tall waves transport heat, energy, carbon and nutrients around the globe. While this is mostly true, huge waves form between layers of water of different density. The deep ocean is thought of as dark, cold and still. Watch UW-produced videos of the research in Samoa.
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