The song of the iceberg

Before the advent of radar and sonar navigation, sailors used to traverse iceberg-littered waters by listening for sounds to indicate how close or how far away an iceberg was. Since the wreck of the Titanic, people have moved beyond the basic human ear to track icebergs, but if we had whale ears, sound might still be sufficient.

That’s because some icebergs can sing. It’s not exactly an aria—more like a cacophonous symphony warm-up—but it still sounds like a song. Unfortunately, it’s not a song we can hear unaided with our unworthy human ears, which cannot detect the very low frequency—about 0.5 Hz—the icebergs emit. It is possible that whales might be able to pick up the sounds since they can detect very low frequencies.

A brief primer on sound

Sound travels in waves, and those waves have frequency—the speed at which they arrive—and amplitude—the size of the wave. Sound is detected when the waves vibrate something; in the case of our own ears, sound waves hit and vibrate the membranes of our inner ears, triggering hair cells that send nervous signals to our brains, where we process the sound. High-frequency waves produce high-pitched sounds, and low-frequency waves produce bass.

Because we can’t hear the low frequencies the singing icebergs emit, their song went undetected until a fluke discovery by a team of earthquake researchers. The team had been using seismic equipment to monitor earthquakes in the Antarctic region. The seismograph produces on paper the frequency and amplitude of vibrations of the earth as movement occurs. An earthquake pattern usually looks like a flurry of large-amplitude events that tapers off and ceases. But the researchers discovered one day a pattern that looked more like a comb—vibrations occurring at regular frequencies and being sustained for a fairly long period of time.

Earthquakes lead to iceberg song

Mystified, they tried to locate the source of the recordings, which seemed to ramble all along the continent’s edge. But it wasn’t until July 2000 that they had a breakthrough. Two small earthquakes triggered a signal that lasted for 16 hours. This event gave them the opportunity to use satellite tracking to pinpoint where the signals were being generated. The epicenter of the quakes turned out to be an iceberg over 1200 feet high that had lodged against an underwater peninsula jutting from the continent. The iceberg was slowly edging its way along the shelf, apparently singing as it went.

The researchers surmised that when the iceberg became lodged, water pressure built up within the crevasses and tunnels that crisscross these floating mountains of ice. The pressure, they speculate, caused water to rush through these deep gulleys and holes, vibrating the walls and producing the “song” of the iceberg. The scientists made a recording of the seismic noise and sped it up, increasing the frequency to a level that human ears could detect. The recording sounds like something between a screech and the playing of a lot of untuned violins. But eventually, it merges into a smooth sound that evokes many stringed instruments playing the same note simultaneously. (Click on the video above to hear.)

From icebergs to volcanoes

The comb-like signal that the iceberg’s vibrations produced is very like what volcanoes produce when they tremble and vibrate. Now that researchers have hypothesized a mechanism to explain the vibrations, they hope to try to apply the concept to volcano models, which are difficult to study because of the heat factor. An iceberg is not the only thing on Earth that consists of a solid substance riddled with tunnels and crevices through which liquid flows, and may serve as a good volcano model.

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Ahem. La-la-la-laaaaaa…squeak

It’s true. They can sing

Male mice can sing. They aren’t exactly sitting underneath an open window on a moonlit night, guitar in hand, crooning an evening serenade to their lady love, but apparently, they do sing for the ladies.

Very few mammals sing. In fact, until the mouse discovery, we and whales were the only verified members of the mammalian choir. Scientists knew that mice vocalize; for example, mice that are surprised or in pain can emit sounds that humans can easily hear, under 30 kHz. Newborn mice can make sounds that their mothers recognize, summoning the dams to make them warm or return them to the nest. And male mice make ultrasonic sounds, above 30 kHz, that the human ear cannot hear. Usually, males make these sounds in response to the smell of an available female.

Birds, mice, whales, people

Because humans and whales make pretty large research animals and ethical issues prevent studies with either, research into how language is learned and how the brain transmits messages about language has relied on birdsong. You may not have thought about it much, but the song a bird sings is really a song, containing repeated melody lines or syllables, and the bird can repeat it given the necessary stimulus. But birds also must learn their songs, and the birds they’re trying to attract must be able to understand them. Because of this requirement for learning, birdsong has been the model for how mammals acquire and learn language.

Birds may be catching a break now, thanks to a recent breakthrough in mouse song. Researchers examined the vocalizations of 45 male mice by placing the mice in a recording chamber. The scientists then inserted through a tube a cotton swab soaked in enough female mouse urine to convince the male to burst into song. After recording the mouse’s vocalization, the researchers manipulated the recordings to so that humans could hear them and then analyzed them using software.

Gus-Gus, is that you?

What they report is that the mice appear to be singing actual songs that contain syllables—very rapidly produced syllables at about 10 per second. In addition, the songs had phrases that the animals would repeat. The mice all seemed to have their own individual songs, and almost all 45 mice sang in response to the urine stimulus.

That mice sing at all was discovered by accident, but the finding that they do sing what appear to be genuine songs opens up a multitude of research possibilities. Among directly related questions to address, scientists must examine how females respond to these calls and whether or not different experiences in fetal development affect the song or success of the song. In addition, scientists must try to demonstrate that the songs are truly learned if the mouse is to be used as a mammalian model for mammalian communication, replacing birdsong.

OK, that’s cute, but why is it relevant?

If the mouse song is learned, the animal will become an important model for these studies. Because mice have been used for decades in genetics studies, there are hundreds of different varieties of mice with genes knocked out or knocked in, and researchers can make their own special strains to assess the effects of a particular gene on song structure or production. We may be able to use this model to identify genes directly involved in learning and communication in mammals.

Identifying these genes could lead to investigations of how developmental processes and differences result in differential learning abilities. For example, people who are autistic exhibit altered communication skills. A stronger understanding of the genetics of mammalian communication may help us to unravel the underpinnings of this aspect of autism and other communication disorders.

These findings also lead to another question that remains to be addressed: Are there other animals that sing a secret song that our ears can’t hear?

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