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The Bloop

The Bloop

The Bloop

15 June 2002
From New Scientist Print Edition.
David Wolman

Even without the beard, Christopher Fox would look nothing like Jodie Foster. Yet as he sits in his office trying to zero in on mysterious sounds emanating from far away, I'm reminded of the scene in Contact where Foster is sitting on her car, wearing headphones and listening for a message from outer space.

Only in this case, Fox is tuned in to unidentified noises from the deep ocean, sounds with strange names like Train, Whistle, Slowdown and Bloop. "Just when you think there're no mysteries left in this world, we have a whole bucket of them on the screen here," says Fox, who directs the US National Oceanic & Atmospheric Administration's Acoustic Monitoring Project at the Pacific Marine Environmental Laboratory in Newport, Oregon.

Earth's oceans are full of noise: boats, whales, submarines and earth tremors all add to the aquatic cacophony. The study of ocean acoustics has helped scientists monitor whale communication and migration, pinpoint the locations of undersea earthquakes and volcanoes, and even measure ocean temperatures, yet there's still a handful of sounds that continue to baffle researchers. They are generally very low-frequency and must be speeded up to be audible. Some last just a few minutes, while others go on continuously for years at a time. Nobody knows for sure what causes these sounds, but suspicion has fallen on volcanoes, icebergs and even huge, undiscovered beasts.

The system that picks up all these signals is a military relic. In the 1960s the US Navy set up an array of underwater microphones, or hydrophones, scattered around the globe. Known as SOSUS, short for Sound Surveillance System, this array was intended to track Soviet submarines. But the end of the cold war, and probably the development of superior surveillance technology, meant that by 1991 SOSUS could be shared with civilian scientists.

These listening stations sit on the seabed at a depth where sounds can travel for thousands of kilometres. Hundreds of metres below the ocean surface, sound waves become trapped in a layer of water known as the deep sound channel. Here the temperature and pressure are such that when sound waves try to move outside this layer, they get bent back into it. So they just keep on travelling. "It prevents the sound from being scattered by either the ocean surface or the ocean bottom, so sound just progresses along merrily without ever hitting anything," says Robert Spindel, a physicist at the University of Washington in Seattle. . . .

Fox's hunch is that the sound nicknamed Bloop is the 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 4800 kilometres 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 whale is lurking in the ocean depths? Or, perhaps more likely, something that is much more efficient at making sound?

In my mind, the suggestion of huge ocean creatures raises a vision of giant squid. There are no confirmed sightings of giant squid in the wild, though dead ones have washed up on beaches, and whales sometimes bear telltale sucker-shaped scars. "We don't have a clue whether they make noise or not," says Fox.

Phil Lobel, a marine biologist at Boston University, agrees that Bloop is likely to be biological in origin but he's not keen on the squid idea. "Cephalopods have no gas-filled sac, so they have no way to make that type of noise. Though you can never rule anything out completely, I doubt it." Lobel thinks the sound is louder than any other whale noise, because I've heard presentations about whale song detected at that distance and farther." . . .