Skyscraper-sized Waves Recorded Beneath the Ocean

For the first time, scientists have recorded an enormous wave the size of a skyscraper breaking at a key location at the bottom of the South Pacific Ocean.

Researchers from the University of Washington recorded the 800 foot wave breaking at a key bottleneck for ocean circulation where water of different density collides. Such massive underwater waves play a crucial role in long-term climate cycles, transporting heat, carbon, and nutrients around the world. Where and how these waves break is important to global climate as well as ocean circulation, the researchers said.

"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. "The primary importance of understanding deep-ocean turbulence is to get the climate models right on long timescales."

Alford led an expedition to the Samoan Passage, a narrow channel in the South Pacific Ocean that funnels water flowing from Antarctica. There, dense water around Antarctica sinks deep into the Pacific, eventually surging through a 25-mile gap in the submarine landscape 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."

The surging water that flows through the gap forms giant submarine waves. Using instruments from their research vessel, Alford and his team observed waves breaking about three miles beneath the ocean's surface. The team's measurements show that when these giant waves break they produce an mixing effect that's 1,000 to 10,000 times greater than what occurs in surrounding slow-moving waters.

"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."

Alford said that the Samoan Passage is important because it mixes so much water, but that deep-sea mixing occurs in waters around the globe, adding that the mixing effect explains why cold water does not permanently pool at the bottom of the ocean.

With a better understanding deep-ocean mixing, Alford said it could help create better simulations of global ocean currents and identify key positions to place instruments to monitor changes.

Alford and his colleagues' research is published online journal Geophysical Research Letters.