Slow waves meander westward out in the deep ocean south of Australia. Sometimes they carry with them carry large eddies, whirlpools over 100 miles across. But every so often, these whirlpools combine into double whirlpools and travel across the ocean 10 times faster than the rest of the whirlpools, moving in sync for months and potentially transporting minerals and nutrients with them.
Scientists announced their observations of these “modons” for the first time in a new paper based on satellite data. These double whirlpools are important for more than just proving a theorised but previously unobserved oceanic anomaly, though. They could perhaps explain a new way to transport water quickly to other parts of the ocean.
“Especially in the Tasman Sea, they represent an unusual pathway for propagation of water with different properties into the open ocean,” the authors write in the study, published this month in Geophysical Research Letters.
Here’s the thing about Earth: It’s a big, spinning ball. That comes with consequences for the things not firmly attached to the planet itself, like the atmosphere and the oceans, which experience a “Coriolis force,” in which some objects’ paths bend as they travel away from or towards the poles. The different amount of bending at different latitudes in the ocean manifests as “Rossby waves,” a slow and westward movement of disturbances in the ocean water.
That creates enormous circles of water called mesoscale eddies, which slowly travel westward—think of these eddies like the ocean weather patterns. Through satellite observations, scientists saw that when two of these eddies link up to create the “modon,” crazy things happen. Rather than travel westward at speeds of 1-2 centimeters per second (like, .02 to .04 miles per hour, literally the speed of a snail), they might travel eastward at 10-20 centimetres per second (a lightning fast .2 to .4 miles per hour, which is perhaps closer to the speed of a tortoise). Sorry if you were picturing super-fast vortexes of ocean water.
These double whirlpools aren’t like, horrible ship-killing storms, nor are they “fast moving” except by comparison to how fast (i.e., very slow) they normally move. But they haven’t been observed before, and the researchers speculate that the behaviour could have important implications for ocean life. These faster-moving whirlpools bring colder water to places where the water is usually warm, and vice versa. Perhaps they even transport food and nutrients for sea life.
The scientists have hit a sort-of limit of how well they can probe these eddies with today’s technology, and hope that new satellites, like the upcoming Surface Water and Ocean Topography satellite, can help increase their understanding.
The exciting thing about this research is that the ocean is still managing to surprise us even today, from its deepest depths to its churning surface. [Geophysical Research Letters]