Above the surface, the ocean seems like a calm, quiet place. Go below, though, and it’s full of sounds – some of which, have never been identified.
Click start to play today’s Spell It, where we listen to the ‘sounds’ of the sea.
Using spectrograms, which are a visual representation of the frequencies that make up a sound, researchers at the US-based National Oceanic and Atmospheric Administration (NOAA) have tracked all kinds of unique soundscapes far below the surface of the ocean. Here are a few that may amaze and surprise you:
1. Earthquakes
The rumble and crack of a growing tremor is often terrifying on land. But what does it sound like when it happens underwater? The NOAA recorded an earthquake near Astoria Canyon, off the coasts of Oregon and Washington, in the US, and the spectrogram presented it as a triangular-shaped signal. Similar to tremors above sea level, the sound of an earthquake under the water swells until it hits a crescendo, and then ebbs away as the tremor passes. It’s a hollow rumbling reverberation that approaches you and then fades away.
2. Blue whales
The call of a Pacific blue whale is one of the best-known marine animal sounds to date. Their vocalisations show up as a number of bands on a spectrogram, since blue whales usually emit a series of pulses and long moans. The NOAA states that they’re among the loudest animals on the planet, and in the right oceanographic conditions, their sounds can be heard by other whales up to 1,600km away. Scientists think their vocalisations are a way of communicating and navigating via sonar, in darker ocean depths.
3. Humpback whales
Humpback whales are another group of marine mammals that generate mesmerising sounds in the ocean. They are capable of creating a wide range of sounds, and have been recorded at their feeding grounds in the waters of Alaska. With moans, grunts, pulse trains and long, complex songs, their vocalisations show up as upsweeping and downsweeping points on a spectrogram.
4. ‘Slow down’ sound
Recorded in May 19, 1997, off the Antarctic Peninsula, researchers heard a sound that gradually descended in frequency over a period of seven minutes. The sound was so loud that three sensors picked it up, across a range of 2,000km. This type of signal had never been heard before, nor has it been heard since. The origin of the sound is still unknown, however, scientists think it is highly probable that a large iceberg could be the source of the sound. A drifting iceberg that ground to a halt as it came in contact with the seafloor, could explain the descending frequency recorded by spectrograms.
5. ‘Bloop’ sound
Another sound that puzzled scientists was repeatedly recorded in the summer of 1997 by hydrophones deployed in the Scotia Sea at the northern edge of the Southern Ocean. The sound rapidly rose in frequency over one minute, and could be heard by multiple sensors at a range of over 5,000km. It very clearly sounded like a ‘bloop’, but its origin remains unknown. However, scientists believe the sound is consistent with that of an icequake, which occurs when large icebergs crack and fracture.
What do you think of these sounds of the sea? Play today’s Spell It and tell us at games@gulfnews.com.
