Video: Black holes of the ocean form inescapable trap

Earth has its own black holes. Swirling masses of water in the ocean are mathematically the same as the warped regions of space-time around cosmic singularities. The finding is more than a mere curiosity: these eddies could be helping to slow climate change.

Oceanic maelstroms can trap and carry billions of tonnes of water over long distances, along with debris and marine life. But because the oceans are constantly churning, it was difficult to pick these cyclones out of the chaos. To know how much water they transport and what their impact on climate could be, we needed a way to locate their edges.

To find them, George Haller of the Swiss Federal Institute of Technology in Zurich and Francisco Beron-Vera at the University of Miami, Florida, created a mathematical model that revealed the similarities between the eddies’ conveyor belt-like edges and a particular region around a black hole. In this so-called photon sphere, light is trapped in loops that spin around the black hole forever.


“The boundaries of water-carrying eddies satisfy the same type of differential equations that the area surrounding black holes do in general relativity,” says Haller.

Seven new eddies

Then they used the model to identify seven previously undetected black-hole eddies in the South Atlantic Ocean off the coast of Africa, using satellite measurements of seawater velocity.

Previous studies had suggested that these eddies, known as Agulhas rings, could carry warm water northwards away from southern sea ice. That could help slow the ice’s melting, which adds cold and less salty water to the oceans, affecting global currents and in turn weather.

The new black hole model could help put new limits on how much warm water is travelling north. “We do not resolve this question in our work, but provide a new technique that could be used in resolving it,” says Haller.

One limitation of the model is that it treats the eddy’s edge as a flat ring, since satellite views do not capture the activity below. This leaves a major question, namely how deep the vortices go, something the team is currently trying to work out. “This will be important in computing the total volume of fluid they carry,” says Haller.

Journal reference: Journal of Fluid Mechanics, DOI: 10.1017/jfm.2013.391