A minke whale in the Ross Sea, Antarctica. Wikimedia Commons
What was that? For decades, mysterious sounds have been recorded from the ocean that have absolutely stumped scientists.
While some remain a mystery, this week, researchers determined that an odd noise known as the "bio-duck" was emitted by an Antarctic minke whale.
Denise Risch of Integrated Statistics and her colleagues explain in the journal Biology Letters that the Donald Duck-type sound is produced by Antarctic minke whales, which they tagged and recorded at Wilhelmina Bay, off the western Antarctic Peninsula.
"For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery," said Risch.
The bio-duck sound is often picked up by hydrophones positioned under the ice of Antarctica.
A whale breaching. Wikimedia Commons
Whales usually vocalize between 17-18 hertz, so scientists are puzzled by a whale-like sound measured at 52 hertz. William Watkins of the Woods Hole Oceanographic Institution first detected it in 1989 while studying U.S. Navy underwater recordings.
The sound remains a mystery. Listen here.
A minke whale. Tony Hisgett, Wikimedia Commons
U.S. Navy submarines located in waters off of Kaneohe, Hawaii, and San Diego, Calif., recorded the "boing" noise. It sounds just like the word, resembling a computer sound effect, but researchers now suspect a minke whale produced it.
A water bubble. Jerry Raia, Flickr
Two hydrophones operating off the South American coast in 1997 captured the mysterious "bloop" sound. The noise resembles a gas bubble rising through water.
Whales are in South American waters, and they are known to pass gas from time to time, so could the sound be that of a whale fart? No one knows, but scientists have ruled out that it was produced by an earthquake, bomb, submarine or volcano.
IcebergAnsgar Walk, Wikimedia Commons
NOAA has dubbed this rather sensual sound "Julia." Recorded on March 1, 1999, the sound was extremely loud and heard over the entire Equatorial Pacific Ocean hydrophone system. While animalistic in nature, the sound's volume and location suggest to researchers that was produced by an iceberg that had run aground.
The Pacific-Antarctic Ridge.Wikimedia Commons
Yet another sound suspected to be an iceberg is the "Slow Down." NOAA recorded it on May 19, 1997, in the Pacific Ocean. The noise, which slowly descends in frequency, sounds like a Halloween haunted house sound effect. Scientists, however, suspect that the recording captured an iceberg running aground on the seafloor.
"Star Wars" lightsabers. Lucius Kwok, Flickr
Ocean scientist Jason Gedamke of the Australian Antarctic Division in Tasmania first heard this sound while on a boat in Australian waters.
He likened it to a lightsaber wielded by characters in the popular "Star Wars" film series. Gedamke and other scientists now suspect that a male dwarf minke whale, trying to attract a female, emitted the noise.
Ben Brooksbank, Wikimedia Commons
NOAA's Equatorial Pacific Ocean autonomous hydrophone array picked up this sound on March 5, 1997. It resembles a train whistle, and with some imagination, the background ambient water sounds resemble a train moving down a track.
According to NOAA, the sound originated from a very large iceberg grounding in the Ross Sea near Cape Adare.
Wind blowing through trees.Yohan euan o4, Wikimedia Commons
The eastern Pacific autonomous hydrophone captured this whirring noise on July 7, 1997. Perhaps the researchers thought it sounded like wind whistling through trees, as it's not a typical whistle noise.
Its origin remains unknown, but the sound's spectrogram resembles that of undersea volcanic eruptions.
This noise, which others have likened to everything from an alarm to a B-movie Martian, has been detected regularly underwater since 1991, when the Pacific Marine Environmental Laboratory began recording for the sound surveillance system known as SOSUS. It appears to be seasonal, occurring most frequently in spring and autumn, but has been dropping off in recent years.
The origin of the haunting sound remains a mystery.