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Deep-Sea "Smoker" Vent's Rumble Reveals Ocean Clues

John Roach
for National Geographic News
February 8, 2007
 
Looks alone suggest that deep-sea vents called black smokers emit a
low rumble as they spew scalding, metal-rich fluids from the bowels of
the Earth.

And in fact they do, according to the first-ever recordings of the phenomena.

The finding breaks a silence, so to speak, that began 15 years ago when researchers last tried to record the vents and heard nothing. The research also suggests that fish and other creatures may use the sounds to navigate the dark depths of the seas.

"Just by looking at them, it is really surprising they wouldn't be making noise," said Timothy Crone, a doctoral student in oceanography at the University of Washington in Seattle.

"They're violent little features."

Water shoots out of the fastest and largest black smokers at about 300 gallons (1,135 liters) a minute—twice the flow from a typical fire hose and enough to fill a bathtub in a few seconds.

Crone and his colleagues reported the findings last month in the Public Library of Sciences' online journal PLoS ONE.

Fluid Flow

The discovery of the sounds may help scientists study how vent flows respond to tides, earthquakes, and volcanic eruptions.

(Read related story: "Deep Sea Volcano Erupts on Film—A First" [May 24, 2006].)

Such information, Crone said, is key to understanding the cycling of chemicals from the Earth's crust into the ocean.

Most instruments used to measure flow, however, are short-lived when inserted in the scalding hot, acidic, and mineral-rich fluid.

Crone thought sound, if detected, could be a way around the problem.

So he and his colleagues plunged deep-sea recording equipment 1.4 miles (2,200 meters) down into a vent field 300 miles (480 kilometers) west of Seattle.

The team recorded 45 hours of sound at a vent called Sully and 136 hours at a vent called Puffer.

"This confirms what was in my gut early on," Crone said.

The researchers suggest the low rumbling sounds mostly result from the flow within the vent structures themselves.

Crone likened the sound to that made by spraying a garden hose against the wall of a house.

In addition, rumbles may be generated as the hot fluid mixes with the frigid sea water and contracts, Crone said.

The rumbles got louder and quieter as the tides went in and out, Crone noted, a phenomenon predicted by numerical models. The changes in volume are thought to be related to changes in flow rate.

"We may have already seen we can measure flow rate change with these types of techniques," he said. "But a lot more work has to be done to be certain of that."

Guiding Sound

When the sounds were analyzed by computer, the researchers also detected resonant tones perhaps generated as the fluid moved over cavities and bumps inside the vent.

"That would also give each vent [its] own particular sound," Crone said. "For me it's hard to tell the difference between them, but if you live down there you might be able to tell one vent from another."

Crone and his colleagues speculate that fish and other sea creatures use these sounds to navigate the deep, dark sea.

(See photos of life around a deep-sea vent.)

"The 'light' of the deep sea is sound, and if something down there is making noise, you can be certain that organisms that can hear are using that piece of information," Crone said.

"It's too good to not pay attention to."

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