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Hydrothermal "Megaplume" Found in Indian Ocean

Brian Handwerk
for National Geographic News
December 12, 2005
 
An enormous hydrothermal "megaplume" found in the Indian Ocean serves as a dramatic reminder that underwater volcanoes likely play an important role in shaping Earth's ocean systems, scientists report.

The plume, which stretches some 43.5 miles (70 kilometers) long, appears to be active on a previously unseen scale.

"In a nutshell, this thing is at least 10 times—or possibly 20 times—bigger than anything of its kind that's been seen before," said Bramley Murton of the British National Oceanography Centre.

Scientists reported the finding last week at the fall meeting of the American Geophysical Union (AGU) in San Francisco. Researchers also announced newly discovered deep-sea hydrothermal fields in the Arctic Ocean and the south Atlantic.

The appearance of hydrothermal vents around the world suggests that they are a far more common part of the ocean system than once believed and could be a major influence on circulation patterns and ocean chemistry.

Scientists are only beginning to identify the tectonic conditions that may indicate where the fields can be found, but the possible locations are increasing.

"I'd be surprised if in the next five years we didn't experience a mini-revolution in terms of finding these [fields] in places where they are not supposed to exist," said geophysicist Robert Reves-Sohn of the Woods Hole Oceanographic Institution.

Volcanic Bombshell

Hydrothermal vents are volcanic hotspots that emit gasses and mineral-enriched water as hot as 760°F (400°C). The heat from these vents supports unique ecosystems where creatures survive using thermal and chemical energy in place of sunlight.

Megaplumes like the one found in the Indian Ocean are probably caused by undersea volcanic eruptions, though scientists aren't yet certain.

"Once formed they can possibly hang around for years," Murton said. The heat from such events could have a dramatic effect on ocean circulation, which plays a role in determining Earth's climate.

"The energy content is an order of magnitude greater [than ordinary plumes], and the thermal power may be many orders of magnitude greater," Murton said.

"A normal hydrothermal vent might produce something like 500 megawatts, while this is producing 100,000 megawatts. It's like an atom bomb down there."

Recent studies have attempted to factor the heat from the world's known hydrothermal ridges into ocean circulation models.

"Some studies estimate that for the Pacific, background thermal heating might increase ocean circulation by up to 50 percent," Murton said.

Regular hydrothermal fields stir the water for only a few hundred meters (about a thousand feet) above the ocean floor. "But these megaplumes can reach a column of 1,000 to 1,500 meters [3,280 to 4,920 feet], so it reaches right up into the midwater," he said.

But even the Indian Ocean megaplume may be small compared to larger underwater eruptions that have as yet gone undetected.

"At the moment those that we've seen have come from small eruptions in the larger scheme of things," he said.

"But we know when we look at the ocean floor that there have been much larger eruptions, so we can only speculate about what magnitude of event plumes would come from those."

The new data on hydrothermal fields and megaplumes underscores the fact that volcanic activity on the ocean floor remains a largely mysterious phenomenon.

"Ninety percent of the Earth's volcanic activity takes place underwater," Murton said. "Just because we can't see it doesn't mean it's not there."

Seafloor Treasures

In addition to their potential impacts on ocean systems, hydrothermal vents provide scientists with a tectonic window below the planet's surface.

The vents essentially form open rifts in the crust that allow chilled water to enter and cool the Earth's interior—offering scientists a peek at the geology inside.

Researchers at the AGU meeting reported on the state of current research to uncover the vents' scientific secrets.

They have determined, for example, that the vents are hotspots for precious metals, such as silver, gold, zinc, and copper.

As yet, these resources lie beyond the reach of commercial interests because mining the ocean floor strains the bottom line.

"The cost of working in the deep ocean is so extreme," explained Reves-Sohn of Woods Hole. "We have the same problem in the scientific community. We don't get to go to look at these places as much as we'd like."

Although active deep-sea hot springs haven't yielded their precious metals to humans, they have surrendered living resources that could prove more valuable.

"The oceans are a chemical soup," said Peter Rona, a marine geologist at the Institute of Marine and Coastal Sciences at Rutgers, the State University of New Jersey.

"And the global diversity of these hot springs reported in these [AGU] sessions adds different chemical ingredients to that soup."

One of these ingredients is the heat-tolerant microbes that provide the base for the vents' ecosystems—converting chemical energy much as plants convert sunlight during photosynthesis.

"To everybody's surprise it is the microbes that live in these vents that are being used first [in commercial applications]," said Rona, who studies the microbes with support from the National Science Foundation and NOAA.

"There are compounds in the microbes that are already being used for industrial and medical applications. Compound enzymes used in detergents, food preservatives, [and] DNA 'fingerprinting' for both research and forensic purposes."

"Also, compounds are being tested by NIH for cancer treatment and other health applications," Rona added. "And it's just the dawn of exploration of these deep sea vents."

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