Title

YYMMDD-0 10.1038/nsuYYMMDD-0 00 Month 2001 category Title Firstname Surname Standfirst.

Lost City of Atlantis vents its secretsBegin text here....

The discovery of new hydrothermal vents could shed light on the origins of life.

Tom Clarke

Researchers have found a 'Lost City' 700 metres beneath the surface of the North Atlantic. The metropolis is inhabited by bizarre bacteria and sea creatures, which are sustained by the hot, mineral-rich sea water that spews into the depths from a newly discovered type of hydrothermal vent system.

The conditions at the vents are thought to be similar to those that existed during the early days of life on Earth, and the bacteria living in the vicinity might be 'living fossils' of the most primitive life forms. The discovery also suggests that hydrothermal vents may be more common and varied than was previously thought.

Oceanographer Deborah Kelley, of the University of Washington in Seattle, and colleagues chanced upon the vent system while investigating an undersea mountain 15 km from the Mid-Atlantic Ridge in an area of the sea floor called Atlantis.

Their find owes its name to the columns of white minerals deposited by the vents, which the team spotted through the murky depths using the research submersible Alvin. One column, measuring 60 metres, is the tallest hydrothermal-vent chimney ever observed.

Finding Lost City was a surprise, says Kelley, because vent systems usually occur on ocean ridges, the only places where magma from inside the Earth gets close enough to the ocean to heat sea water and drive hydrothermal vents. Here, minerals from the magma are ejected as black plumes reaching temperatures of 300 ºC.

But Lost City is far from an ocean ridge, releases white carbonate minerals, and has a temperature of between 40 and 70 ºC. Its discovery "opens up much larger areas of the sea-floor that can support hydrothermal vents and associated life than we thought before", says Kelley.

Oceanographers had predicted that chemical reactions between sea water and the rocks beneath the sea floor could create vents away from ocean ridges. The discovery of Lost City and analysis of the minerals in its fluids confirm this idea, Kelly says.

Although Kelly's team only saw a few large animals - mostly crabs, sponges and corals - living in Lost City, the vent chimneys teem with bacteria. In some places, says Kelley, "you can't even see the rock because of the amount of bacteria".

Initial studies of these microbes show that they belong to very ancient groups that can survive on a diet of minerals and organic compounds such as methane.

Researchers are keen to learn more about Lost City's bacteria because the bugs thrive in the alkaline conditions associated with carbonate rocks. Conditions on Earth over three billion years ago, when life emerged, are thought to have been much the same.

"It's a really important find," says Karen Von Damm at the University of New Hampshire in Durham, who studies hydrothermal vents. "It shows that there are still a lot of things down there we don't know about."

reference

1. Kelly, D. S. et al. An off-axis hydrothermal-vent field near the Mid-Atlantic Ridge at 30° N. Nature 412, 145-149 (2001).