Marine life and the loud sound of ships crossing the waters make the ocean a noisy place, but amid all these noises, scientists were able to detect a strange and powerful sound coming from a popular part of the Atlantic Ocean, the Caribbean Sea.
The whistle-like noise may be too low for it to be heard by the human ear, but it is so powerful that researchers said its signature can be detected from space.
Chris Hughes from the University of Liverpool and colleagues detected the sound while studying ocean dynamics in the Caribbean Sea. They also noticed something odd in the pressure oscillations across the basin.
"We were looking at ocean pressure through models for quite different reasons, and this region just didn't work," Hughes said.
The researchers conducted further investigation. They analyzed the sea level and pressure readings of the bottom of the Caribbean Sea between 1958 and 2013 and looked at satellite gravity measurements and tide gauges.
It turned out that the strange pressure oscillations happen in real life and do not just show up in the models. They also produce a low noise that can be described as a whistle.
The noise, the "Rossby Whistle" occurs as a result of the interaction between Rossby waves — large waves that travel to the west in the ocean — and the seafloor.
The waves disappear at the west of the Caribbean basin, but resurface on the basin's eastern side after 120 days. It is basically water sloshing in and out of the Caribbean basin over a defined period. The interaction between the wave and the seafloor causes the region to whistle.
"We show that an important source of coastal sea level variability around the Caribbean Sea is a resonant basin mode," the researchers wrote in their study which was published in the Geophysical Research Letters on June 19.
"The porous boundary of the Caribbean Sea results in this mode exciting a mass exchange with the wider ocean, leading to a dominant mode of bottom pressure variability."
This mass change is enough to produce changes to Earth's gravitational field that can be measured from satellites.
Hughes said that the ocean activity in the Caribbean Sea is comparable 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," Hughes said. "Because the whistle is open, the sound radiates out so you can hear it."
Researchers said that the whistle-like noise likely plays a note of A-flat, albeit it is many octaves below the range that can be heard by the human ear.