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Strange Underwater Sounds

A while back I wrote a post about the 52 Hz Whale, and this post is going to be like that one, on the subject of strange underwater sounds.

Soectogram of the Bloop

In 1997, the NOAA recorded an extremely strong underwater sound with an ultra-low frequency. Today, it is known as the "bloop" because of the sound of it. The sound was recorded off the west coast of South America. The NOAA said of the sound: "It rose rapidly in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 kilometers (3,000 miles)." The NOAA did not believe that something man-made created the sound. So what was it, being several times louder than the sound of a blue whale, the largest recored animal?

The official answer is that it is nothing more than an icequake. But, there are some who think it may be a massive animal, a true leviathan. Dr. Christopher Fox of the NOAA has said that it may actually be from an animal. David Wolman, a journalist, describes Fox's idea:

"Fox's hunch is that the sound nicknames Bloop is most likely to come from some sort of animal, because its signature is a rapid variation in frequency similar to that of sounds known to be made by marine beasts. There's one crucial difference, however: in 1997 Bloop was detected by sensors up to 4,800 kilometers (3,000 mi) apart. That means it must be far louder than any whale noise, or any other animal noise for that matter. Is it even remotely possible that some creature bigger than any blue whale is lurking in the ocean depths? Or, perhaps more likely, something that is more efficient at making sound?"

Why would it be impossible for something bigger than a blue whale to exist? The oceans are a vast, largely unknown place.


The NOAA first recorded this odd sound in 1991. Called the "Upsweep," it "consists of a long train of narrow-band upsweeping sounds of several seconds in duration each. The source level is high enough to be recorded throughout the pacific."

Since 1991, the source level of the sound has decreased but it can still be heard, and appears to reach peaks in the spring and autumn.


On March 1, 1999, the NOAA recorded a sound called "Julia." The sound lasted 15 seconds and was loud enough to be heard over the whole Equatorial Pacific Ocean autonomous hydrophone array. The NOAA's conclusion concluded the sound most likely come from a large iceberg that had run aground in Antarctica.
Julia spectogram

Slow Down

The "Slow Down" was recorded by the NOAA on May 19, 1997. The sound lasts several minutes and decreases in frequency over that time (hence the name). The sound, like Upsweep, has been recorded each year since '97. Again, it is thought to be from a large iceberg.


The Whistle was recorded by the NOAA on July 7, 1997. It is "mysterious audio of what resembles distant whirring." It is thought it is caused by eruptions of underwater volcanoes.


The "Train" sound was recorded on March 5, 1997. Again, the NOAA concluded it is likely from a large, grounded iceberg.

Train sound


The "Bio-Duck" sound was first detected by submarines in the 1960s. It was recorded in the open ocean, along the Australian coast, and Perth Canyon. It has now been identified as coming from Antarctic minke whales.


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