Remarkably, the culprits are the waves, hiding in plain sight. Sometimes, large waves in the basin move towards the west, and these inevitably interact with the seafloor. This deflects it somewhat, causing it to fade out on the western boundary and appear on the eastern section of the basin, almost as if it jumped through a wormhole in the fabric of space.
Over time, these slow waves interact in a constructive manner, amplifying them for a while. The net result of all this is that water propagates en masse in and out of the basin every 120 days. This wave pattern, just like the sound wave of someone singing, produces a clear A flat, albeit one too many octaves below the range of human hearing. The huge amount of water moving back and forth changes the local gravitational field, which can be detected beyond Earth’s upper atmosphere.
“We can compare the ocean activity in the Caribbean Sea to that of a whistle,” Chris Hughes, a professor in Sea Level Science at UL, said in a statement. “When you blow into a whistle, the jet of air becomes unstable and excites the resonant sound wave which fits into the whistle cavity. Because the whistle is open, the sound radiates out so you can hear it.”
The “Rossby Whistle,” tracked by the motion of the Rossby Waves. It has been pitched up here so you can hear it. University of Liverpool/Science Alert/Chris Cassella via YouTube
As the westward-moving wave is called a Rossby Wave, they have decided to call the noise the Rossby Whistle. So although it’s not Cthulhu calling, it’s still pretty cool.
Just recently, another low-frequency hum was heard emanating from a shadowy region of the oceans known as the “twilight zone.” In this case, it was being produced by life – lots of it, in fact. As it turns out, the upward migration of fish, moving into the light to feed, was producing what the researchers termed their “dinner bell”.