An ultimate wave has been found in the Pacific but it will never be ridden by a surfer. It breaks at a height of about 240 metres - and it is at the bottom of the ocean.

For the first time, waves that crash through a choke point called the Samoan Passage have been measured by University of Washington scientists.

As dense Antarctic bottom water, a key driver of global ocean circulation, forces its way north, it funnels into this passage deep below the Pacific's surface, oceanographer Matthew Alford said.
''Basically the entire South Pacific flow is blocked by this huge submarine ridge,'' Professor Alford said.

''The amount of water that's trying to get northward through this gap is just tremendous - 6 million cubic metres of water per second, or about 35 Amazon rivers.''

Just like a wave on a beach or a point, water rises and collapses. As it rushes through, the ridge forms a lee, the water becomes unstable and turbulent, and breaks.

Professor Alford's team found the phenomenon when they lowered instruments five kilometres under the surface at the passage, just north of the Samoan islands - about 4500 kilometres north-east of Brisbane - in an expedition last year.

He said in a study published in the journal Geophysical Research Letters this week that the passage's breaking waves mixed water at a rate of up to 10,000 times greater than surrounding slow-moving 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,'' Professor 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.''

Professor Alford's Wavechasers group has sailed the world to measure undersea waves, which he said travelled across oceans, and were powerful enough to force submarines to hit the bottom, or breach the surface. As mixers of seawater around the planet, they also had a strong influence on climate, he said.