What's That Strange Sound Coming From the Caribbean Sea?

The sea is a noisy place, but there's also a sound that no humans can hear. Chris/flickr

Even if you listened carefully, you wouldn't be able to hear the strange sound researchers recently detected coming from the Caribbean Sea.

The sound is too low-pitched for humans to hear, but University of Liverpool ocean scientists say this region acts like a whistle that blows so loudly it can be "heard" from space. How? It's complicated, but it has to do with how certain waves produce an oscillation of the Earth’s gravity field.

Researchers analyzed sea levels and pressure readings taken from the bottom of the Caribbean Sea from 1958 to 2013. They also used data from tide gauges and satellite gravity measurements.

They noticed a phenomenon they named a Rossby whistle. It's what they say happens when a Rossby wave — a large wave that travels slowly from east to west across the ocean — interacts with the seafloor. The wave dies out at the western boundary, only to reappear on the eastern side, creating a Rossby wormhole. Researchers found that only waves of certain lengths can survive the whole process and when they do, they produce an oscillation. Specifically, the sound is A-flat.

Researcher Chris Hughes, an expert in sea level science at the University of Liverpool, said in a news release: “We can compare the ocean activity in the Caribbean Sea to that of a whistle. 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."

You can hear a version of it here:

Other than just being really cool, Hughes says understanding the phenomenon can help predict the likelihood of coastal flooding.

“This phenomenon can vary sea level by as much as 10 cm along the Colombian and Venezuelan coast, so understanding it can help predict the likelihood of coastal flooding,” he said.

The study was published in the journal Geophysical Research Letters.