Scientists at the University of Liverpool have observed “double whirlpools” in the natural world for the first time. Until now, the unusual fluid dynamics phenomenon had only been theoretically envisioned. While eddies, whirlpools that can span hundreds of miles in the open ocean, are not uncommon, two connected eddies spiraling in opposite directions was previously unheard of. “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 Chris Hughes, study lead-author and University of Liverpool oceanographer.
The double-whirlpools are known as modons and were suspected to exist for decades, though scientists had never acquired hard evidence of their existence. This changed when Hughes began to closely study satellite footage of the ocean surrounding Australia. “I happened to notice one little feature down in the Tasman Sea [between Australia and New Zealand] that was behaving very strangely compared to everywhere else,” Hughes told Popular Science. “Almost all these eddies drift slowly westwards, but this little feature was going quickly eastwards.”
After further investigation, Hughes and his team learned that modons are not actually as rare as once thought. Satellites had been recording images of the phenomenon for decades, though scientists had not known where to look for them. Although there is still much research to be done, scientists believes that a double-whirlpool may form when two whirlpools collide with each other in the ocean. It is also possible that modons emerge as a result of friction impacting a whirlpool close to the coast. After formation, a modon casts a U-shaped underwater vortex and can endure for up to six months.
Given their size and speed, modons may play an important role in ocean ecology. “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,” Hughes said. “You would get particular blobs of water where the biology and the conditions are totally different from the surrounding area. 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.”