Media contacts: NSF: Cheryl
Dybas (703) 292-8070
NSF PR 00-93 Duke University: Monte
Basgall (aboard ship)
Dave Epp (703) 292-8582
Images Available: http://www.nsf.gov/od/lpa/news/press/00/pr0093.htm
HYDROTHERMAL VENT SYSTEM FOUND ON SEAFLOOR
dubbed "Lost City"
A new hydrothermal vent field, which scientists have dubbed "The
Lost City," was discovered December 5th on an undersea mountain in
the Atlantic Ocean. The unexpected discovery occurred at 30 degrees
North on the Mid-Atlantic Ridge during an oceanographic cruise aboard
the research vessel Atlantis. A team of scientists from the
Scripps Institution of Oceanography, Duke University, the University of
Washington and other institutions conducted the National Science
Foundation (NSF)-supported expedition. "We thought that we had seen
the entire spectrum of hydrothermal activity on the seafloor, but this
major discovery reminds us that the ocean still has much to reveal,
"says Margaret Leinen, NSF assistant director for geosciences.
"These structures, which
tower 180 feet above the seafloor, are the largest hydrothermal chimneys
of their kind ever observed," said Deborah Kelley, a University of
Washington geologist and co-principal investigator on the cruise.
"If this vent field was on
land, it would be a national park," added Duke University
structural geologist Jeff Karson, a second co-principal investigator
who, along with Kelly, dove in the submersible Alvin to the site.
Perhaps most surprising is that
the venting structures are composed of carbonate minerals and silica, in
contrast to most other mid-ocean ridge hot spring deposits which are
formed by iron and sulfur-based minerals. The low-temperature
hydrothermal fluids may have unusual chemistries because they emanate
from mantle rocks.
Nothing like this submarine
hydrothermal field has ever been previously observed, say the
scientists. These events are unique, they believe, because they rest on
one-million-year-old ocean crust formed tens of kilometers beneath the
seafloor, and because of their incredible size. Dense macrofaunal
communities such as clams, shrimps, mussels, and tube worms, which
typify most other mid-ocean ridge hydrothermal environments, appear to
be absent in this field.
The Lost City Field was
discovered unexpectedly while studying geological and hydrothermal
processes that built an unusually tall, 12,000-foot-mountain at this
site. In this area, deep mantle rocks called serpentinized peridotites,
and rocks crystallized in subseafloor magma chambers, have been uplifted
several miles from beneath the seafloor along large faults that expose
them at the surface of the mountain.
"As so often happens, we
were pursuing one set of questions concerning building of the mountain
and we stumbled onto a very important new discovery," said Donna
Blackman, a geophysicist from the Scripps Institution of Oceanography
and chief scientist of the expedition. She added that "the venting
towers are very spectacular and, although they bring up a whole new set
of questions, we will learn about the evolution of the mountain itself
as we study the vents carefully in the future."
Observations using the
submersible Alvin and deep-towed vehicle Argo,
operated by Woods Hole Oceanographic Institution, show that the field
hosts numerous active and inactive hydrothermal vents. The steep-sided,
180-foot-tall deposits are composed of multiple spires that reach 30
feet in width at their tops. They are commonly capped by white, feathery
hydrothermal precipitates. The tops and sides of the massive edifices
are awash in fluids that reach temperatures up to 160 degrees.
From the sides of the
structures, abundant arrays of delicate, white flanges emerge. Similar
to cave deposits, complex, intergrown stalagmites rise several meters
above the flange roofs.
Underneath the flanges, trapped
pools of warm fluid support dense mats of microbial communities that
wave within the rising fluids. Downslope, hundreds of overlapping
flanges form hydrothermal deposits reminiscent of hot spring deposits in
Yellowstone National Park. During the Alvin dive, expedition
leader Patrick Hickey collected rocks, fluids, and biological samples
for shore-based analyses.
"By studying such
environments, we may learn about ancient hydrothermal systems and the
life that they support," suggested Kelley.
Notes to editors and reporters:
For samples of photos, see: http://www.nsf.gov/od/lpa/news/press/00/pr0093.htm
The three principal scientists
may be contacted aboard ship until Sat. Dec.16:
As of Monday, Dec. 18, they may
be reached at their home institutions through their press officers:
University of Washington: Sandra
Hines (206) 543-2580/
Scripps Institution of
Oceanography: Cindy Clark (858)
Duke University: Dennis
Meredith (919) 681-8054