Scientists from the Naval Research
Laboratory (NRL) and the University of Bergen, Norway, have used
sediment cores, heat flow, and bathymetric measurements to discover
an active gas seep and mud volcano. The scientists' studies revealed
that a 1-km-diameter circular feature, previously detected by
an NRL-led sidescan sonar mapping project on the continental
slope northwest of Norway, was a gas seep and mud volcano.
The discovery, the first of this
kind in high-latitude (72 degrees north) oceanic areas, was made
on an NRL-led research cruise aboard the Norwegian vessel Haakon
Mosby, the same ship that had towed the sidescan sonar in
prior years. Dr. Peter Vogt, of NRL's Marine Geosciences Division,
and Professor Eirik Sundvor, University of Bergen, Norway, were
co-chief-scientists.
The circular feature was identified
as a "gas seep" because hydrogen sulphide (H2S) and
methane hydrate were abundant in the sediment cores, and acoustic
returns also suggested gas bubbles in the water column. A new
species of worm was recovered and shown to be of the type dependent
on chemosynthetic bacteria which utilize methane and/or hydrogen
sulphide. The gas seep is at the same time interpreted as a "mud
volcano" because of its mound-like shape and the presence
of a halo of weak acoustic backscatter material, thought to be
sediment oozing out of the mound and flowing into a shallow moat
surrounding the mound, according to Dr. Vogt.
The heat flow, measured by Professor
Sundvor, is one of the highest ever measured in the world ocean
away from active plate boundaries or mid-plate "hotspots"
such as Hawaii. Sediment recovered near the heat flow station
reeked of H2S, and methane hydrate (clathrate) crystals were
observed at the bottom of a 2m-long core. These crystals fizzed
away at the ambient atmospheric pressures, but this was the first
direct observation of methane hydrate along the continental margin
from Norway north to Spitzbergen and the Arctic. In this large
region, NRL had previously predicted methane hydrate's existence,
and Norwegian scientists had reported seismic reflection evidence
for the hydrate from parts of this region.
Further investigations, including
deep-tow video, sccheduled for August 1996 aboard a Russian vessel,
may find more evidence for this gas venting and chemosynthetic
life at the newly identified gas seep and other, similar sidescan
sonar features not yet investigated, but now suspected to have
a similar origin.
A small portion (50 x 50 cm)
of the mud volcano's surface was recovered with a box corer on
the recent Mosby expedition. A sample of the mud, containing
almost 200 of these vermicelli like pogonophoran tube worms,
was later examined by Dr. Roman V. Smirnov of the Zoological
Institute, St. Petersburg, Russia. Dr. Smirnov identified these
worms as a new species of the genus Sclerolinum. The six previously
known Sclerolinum species all hail from Antarctic waters; none
are known so far from middle latitudes, notwithstanding the uniformly
low temperatures of the deepwater oceans.
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