"Double whirlpools" observed for first time

For the first time, scientists have recorded a bizarre phenomenon in fluid dynamics, which up until now had only ever been theoretically predicted, but never observed in the wild.

Huge whirlpools known as eddies, which can measure hundreds of kilometers across, are relatively common, however now it turns out that, under certain conditions, pairs of these swirling vortices can actually join together to form double whirlpools capable of traveling large distances across the sea.

"Ocean eddies almost always head to the west, but by pairing up they can move to the east and travel ten times as fast as a normal eddy, so they carry water in unusual directions across the ocean," said oceanographer Chris Hughes from the University of Liverpool.

"What we found was a pair of eddies spinning in opposite directions and linked to each other so that they travel together all the way across the Tasman Sea, taking six months to do it."

It turns out that these double whirlpools, which have been dubbed 'modons', have been appearing on satellite imagery for decades, but until now nobody had known what they were.


"My thinking is that these linked, fast moving eddies could 'suck-up' small marine creatures and carry them at high speed and for long distances across the ocean," said Hughes.

"You would get particular blobs of water where the biology and the conditions are totally different from the surrounding area," Hughes told Popular Science.

"It's quite possible there are shoals of particular types of fish following these eddies for their special conditions. Fish would actually actively follow the eddies by choice because of what's in them."
The findings are reported in Geophysical Research Letters.