3 MAR 2005
Scientists floored by the ocean floor
On the side of a giant undersea mountain east of Bermuda, a group of oceanographers
has found a unique ecosystem that may, conceivably, be a birthplace of
life. 
In
2000, Deborah Kelley of the University of Washington, and a group of colleagues
were monitoring an undersea camera when some giant, irregular white columns
hove into view.
"Everybody knew it was something very different," she says.
Adapted from original map at USGS.
When you find something new, you get to name it. The researchers named their forest of chimneys "Lost City," even though it's not a city, and it was never lost. The finders dubbed the goliath of the spires "Poseidon," after the Greek god of the sea. Poseidon soars 60 meters -- almost 200 feet -- above the sea floor.
Return dives in 2003 drew a better picture of the peculiar white structures, which act as exhaust ducts for warm, carbonate-rich seawater and are built of carbonate rocks, much like stalagmites in a cave.
A pinnacle venting carbonate solution on Poseidon,
a 60-meter-tall carbonate structure fed by hot water on the bottom of
the Atlantic. Small, delicate flanges host dense arrays of filamentous
bacteria nourished by methane and hydrogen in the water. Right: arm of
the submersible Alvin. Courtesy University of Washington
The chimneys cover three to four hectares of mountainside at a depth of about 800 meters. Similar complexes probably exist, Kelley says, but have not been seen because ocean-floor scientists have focused on the bizarro "black smoker" structures near the mid-oceanic ridges. The white chimneys are 15 kilometers from the Mid-Atlantic ridge.
If your submarine and support ship cost $35,000 a day, you tend to look in places where you know you will find something worth writing home about...
Alvin
is a friend indeed when you need to explore the deep ocean.Photo:
Woods Hole Oceanographic
Institution
Really smokin'!
When the black smokers were found in 1979, they were really something.
Covered with microbes and animals, they proved that life could exist in
the deep ocean, even without sunlight, the energy source for almost all
life. The white columns at Lost City give a contrasting picture of life
in the depths:
Black
smokers are vents that allow volcanically heated water to escape
the sea floor. The water is superheated, acidic, and charged with metals
like iron, copper and sulfur. At Lost City, seawater is heated by a chemical
reaction under the sea floor. The water emerges at a much cooler temperature,
but it's as alkaline as drain cleaner.
Microbes
at black smokers metabolize the volcanic gas carbon dioxide
and can also use metal, while those at Lost City eat methane and hydrogen.
Black
smokers are covered with weird animals like "tube worms." Lost
City has more animal species -- but they are smaller and less abundant.
A flange deposit growing from a chimney. Hydrothermal fluids pool under the flange and flow out under its lip. That extends the flange, which is about a meter long. Courtesy University of Washington
Like the smokers, the white chimneys are formed and governed by the unusual
chemistry of the water inside them. When seawater reacts with rocks within
the mountain, alkaline fluids are formed. 
When
these fluids mix with seawater, carbonate minerals precipitate to form
the chimney structure. The reaction also produces hydrogen and methane,
which become "the whole basis of the food chain for microbes," says Kelley.
Which came first?
You may know that the hot springs at Yellowstone and elsewhere are considered
candidates for the birth of life -- since the microbes found in them (and
at the white chimneys and black smokers) are ancient, primitive bacteria
in the group Archaea. Could the Lost City researchers have stumbled across
a birthplace of life?
It's possible. "Early in Earth's history, says Kelley, "volcanic rocks on the seafloor were more like the mantle rocks at Lost City. One hypothesis is that as soon as there were oceans on the planet, these rocks were available to interact with seawater, and that could have made a hydrothermal system like Lost City."
Not convinced? You shouldn't be. 
This
is speculation. But think about this: The Lost City chemical reactions
make propane and acetate, two hydrocarbons that might have been handy
for the most primitive forms of life.
The top of a 30-meter carbonate pinnacle. The pores, nooks and crannies are all habitat for microbes and small animals. Courtesy University of Washington
And elderly rocks that may still retain traces of ancient bacteria are "shot through with veins of carbonate, like what we see under Lost City," Kelley says.
-- David Tenenbaum
Bibliography
A Serpentinite-Hosted Ecosystem: The Lost City Hydrothermal Field,"
by D.S. Kelley et al, Science, Mar. 4, 2005.
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