The Bahamas, as seen from space. There's something in the water... Tim Peake/NASA/ESA

Scientists love a good mystery, and the oceans of the world – being massive, deep, dark, and inherently enigmatic places – are literally full of them. The latest conundrum comes courtesy of the Caribbean Sea, wherein a very low-pitch sound, one well beyond the hearing range of humans, can be heard. In fact, something down there is so huge and mobile that it's generating waves in Earth’s gravitational field.

A team of researchers, led by the University of Liverpool (UL), were in the middle of conducting an expedition to the Atlantic Ocean-based Caribbean Sea, which covers an area of roughly 2,754,000 square kilometers (1,063,000 square miles). Their original objective was to study the dynamic sea currents within the basin, which links up to the Gulf Stream, critical for delivering heat to, among other places, Western Europe.

Writing in the journal Geophysical Research Letters, the authors describe how their instrumentation picked up something they describe as a “whistle”. The note itself is an A-flat. Something quite sizeable is clearly making its presence known, but initially, it was unclear whether the noise was emanating from something living or another natural process.

It's probably not this. Antonio Maletin/Shutterstock

Taking sea level and pressure readings from the bottom of the basin, assessing the frequency and magnitude of the regional tides, using satellites to measure small changes in the local gravity, and feeding this all into multiple models of oceanic current activity based on a period of time from 1958 to 2013, the team began to suspect the noise was not, sadly, coming from a gigantic sea monster.