NSF PR 97-17 - February 28, 1997
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Feature: "Baked Alaska" Mud Volcano Discovered
in North Atlantic
Researchers on a cruise have confirmed that a hot
mud volcano on the sea floor between Greenland and
Norway is oozing mud, seeping gas and spewing a gas-laden
plume of warm water into the North Atlantic. Frozen
methane hydrate caps the volcano, whose slopes are
inhabited by a new species of tube worm most closely
related to a group found in Antarctica.
The rare juxtaposition of heat vents on the sea floor
with a frozen methane cap has led Hunter College geophysicist
Kathleen Crane, who studied the feature on a cruise
last August, to dub it a "baked Alaska" complex. The
methane hydrate is a white, ice-like solid made up
of water and gas that can compress a huge amount of
gas within its crystal lattice.
Frozen methane has been found within the ocean floor
but rarely, as in this case, atop the floor. Methane
should dissolve or oxidize in sea water, so its presence
suggests that it must be in constant production, according
to Naval Research Laboratory geophysicist Peter Vogt,
a chief scientist on the cruise. Another theory, however,
is that some of the white features are actually bacterial
mats.
On the latest cruise to investigate the site, using
the Russian vessel Professor Logachev, scientists
supported by the National Science Foundation, Naval
Research Laboratory, Office of Naval Research and
Russian and Norwegian institutions confirmed the existence
of the mud volcano, a rare phenomenon in the deep
ocean. Located 1250 meters deep, the volcano is about
one kilometer in diameter, is encircled by a moat,
and has "a gross cowpie shape," according to Vogt.
The team, also led by Russian chief scientist Georgy
Cherkashev, spotted a similar feature in the area
that may be a second volcano.
The flow of heat rising within the volcano (up to
one or more watts per square meter) is one of the
highest measured in the ocean, apart from the boundaries
of tectonic plates or "hot spots" such as Hawaii.
What is generating this heat and setting the gas,
fluid, and mud into motion is still a mystery. Vogt
suggests that the cause could be the gravitational
instability of the marine sediments, which were deposited
very rapidly by glaciers; or alternatively, the "dewatering"
or extrusion of water by the sediments. Crane, on
the other hand, proposes that the volcanism may indicate
that an ancient fracture between the Greenland Sea
oceanic crust and the Barents Sea continental crust
is still active, serving as a crack for heat and fluids
to rise up to the seafloor.
Like communities of life at other hydrothermal vents
in the oceans, the mud volcano's colonies of vermicelli-like
worms ultimately derive their energy not from photosynthesis
but from seeping gas.
The matted tangles of tube worms, twisted across the
mud like telephone cord, live in association with
fish and other life. They are a new species of the
genus Sclerolinum, whose six other species
live on the other side of the globe in Antarctic waters.
A quill-like tube extends from each worm into the
odorous mud. When brought to the surface, mud samples
crackle like frying bacon and reek of hydrogen sulfide
as gas bubbles are released from decomposing hydrate
by the change in pressure. Small bottom-fish resembling
salamanders, probably a species of eelpout, appear
to be grazing on the tubeworm "lawns."
Carbon isotopes from the worms show that they derive
their energy not from "oceanic snow" -- dead organic
matter sifting down from above, and originally produced
by photosynthesis -- but rather through chemosynthesis,
living off the seeping methane and possibly also the
hydrogen sulfide. It is actually the bacteria living
in symbiosis inside the worms' cells that appear to
"feed" on the gases, providing the energy for the
worms to live.
Over recent decades, gas hydrates at the ocean bottom
have attracted attention as a potential energy source,
twice as extensive as the burnable carbon stored in
all other fossil fuels. Scientists also propose that
the methane locked up in hydrates, such as the one
capping the volcano, could play a role in climate
change. If sea level dropped -- during an ice age,
for example -- pressure on this stored gas could ease,
ultimately releasing the gas into the atmosphere and
causing greenhouse warming.
The scientists hope to visit the site again this year
in Russian deep-diving submersibles to sample the
biotic community and carry out experiments on the
methane-hydrate cap, including research on the possibility
that solid hydrate particles float up into the water
column.
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