Amusing Monday: Mysterious ocean sounds are not always ‘creepy’

Some underwater ocean sounds remain a mystery, while other sounds are well understood by NOAA’s Pacific Marine Environmental Laboratory.

PMEL’s acoustic division continues to find unusual sounds within its long-term mission of recording and measuring ocean noise and assessing potential problems created by noisy humans.

Sounds ranging from whale calls and volcanoes to cargo ships and airguns are monitored by the Pacific Marine Environmental Laboratory with the help of 11 Ocean Noise Reference Stations from Alaska to the South Pacific. Graphic: NOAA's Pacific Marine Environmental Laboratory
Sounds ranging from whale calls and volcanoes to cargo ships and airguns are monitored by the Pacific Marine Environmental Laboratory with the help of 11 Ocean Noise Reference Stations.
Graphic: NOAA’s Pacific Marine Environmental Laboratory

I remain intrigued by ocean sounds, and I can’t help but worry about sensitive marine creatures, such as whales, that must live in our modern world of noisy ships and machinery.

One mysterious sound nicknamed “Upsweep” was present when PMEL began recording on the Navy’s SOSUS (Sound Surveillance System) array in August 1991. The sound, which consists of a series of upsweeping sounds, is loud enough to be heard throughout the Pacific Ocean, according to PMEL’s website. This sound was speeded up 20 times to be more easily heard.

      1. Upsweep-PMEL

The sound is loudest in spring and fall, but researchers have not been able to figure out whether that is the result of changes in the sound source or propagation conditions in the water. The sound has been declining over the past 25 years. The cause has not been determined, but the sound is originating from an area believed to be seismically active between Australia and the southern tip of South America.

PMEL has three ocean acoustic research groups:

  • Geophysics: Monitoring for underwater earthquakes and volcanic activity and using sound to determine the precise location.
  • Bioacoustics: Using sound to study the distribution of large whales in the ocean.
  • Ambient sound: Studying background sounds, both natural and man-made, and their effects on marine ecosystems.

Other well-known sounds recorded (and speeded up) by PMEL with their nicknames:

Whistle

Recorded on a hydrophone off the west coast of Mexico in July 1997, this wavering sound is characteristic of a volcanic eruption under the sea, according to the PMEL website. With only one hydrophone capturing the sound, it was not possible to determine a precise location, although the sound is similar to other eruptions in the Mariana volcanic arc.

      2. Whistle-PMEL

Bloop

Another broad-range sound recorded in the summer of 1997 is a very distinctive “bloop,” which provided the nickname. This and other recordings are associated with large icebergs as they crack and fracture. Sounds were used to track one iceberg after it broke away from Antarctica and disintegrated off South Georgia Island in the South Atlantic Ocean in 2008, according to the PMEL website.

      3. Bloop-PMEL

Julia

You can imagine an iceberg scraping along the bottom of the ocean as you listen to this sound and hear the tone go lower and lower. Researchers suspect the incident occurred between Bransfield Strait and Cape Adare in Antarctica, according to the PMEL website. Also known as “slow down,” I haven’t been able to figure out why it is called “Julia,” but the sound has been described as “creepy” by some people.

      4. Julia-PMEL

Train

Another iceberg grounding in March 1997 produced a sound like a train whistle off in the distance. This iceberg grounded in the Ross Sea of Antarctica, somewhere near Cape Adare, according to the PMEL website.

      5. Train-PMEL

Small ship

I don’t know about anyone else, but it seems to me that man-made noises are especially annoying. Here, an unidentified ship produces a “banded spectrogram” caused by the repetitive pulsing of the ship’s propeller, according to the PMEL website. Experts use the frequency bands and other characteristics of the spectrogram to identify the type of ship.

      6. Small-ship

Mariana Trench

Early this year, researchers dropped a hydrophone to the bottom of the Mariana Trench, 36,000 feet down — nearly 7 miles — in a place called Challenger Deep. It took six hours for the equipment to reach the bottom.

“You would think that the deepest part of the ocean would be one of the quietest places on Earth,” said NOAA research oceanographer Robert Dziak in a news release. “Yet there really is almost constant noise from both natural and man-made sources.

“The ambient sound field at Challenger Deep is dominated by the sound of earthquakes, both near and far, as well as the distinct moans of baleen whales and the overwhelming clamor of a category 4 typhoon that just happened to pass overhead.”

A specially designed instrument was needed to withstand the vast pressures at that depth, according to Haru Matsumoto, an Oregon State ocean engineer who collaborated with NOAA engineer Chris Meinig in the design.

“We had never put a hydrophone deeper than a mile or so below the surface, so putting an instrument down some seven miles into the ocean was daunting,” Matsumoto said in the news release. “We had to drop the hydrophone mooring down through the water column at no more than about five meters (16 feet) per second. Structures don’t like rapid change and we were afraid we would crack the ceramic housing outside the hydrophone.”

      7. mariana1


      8. mariana2

Previous Water Ways entries on the subject of sound:

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