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October
19, 2006
METHANE
DEVOURER DISCOVERED IN THE ARCTIC
Not
lava, but
muds and methane are emitted from the Arctic deep-water mud volcano
Haakon
Mosby. When it reaches the atmosphere, methane is an aggressive
greenhouse gas,
25-times more potent than carbon dioxide. Fortunately, some specialized
microorganisms feed on methane and thereby reduce emissions of this
greenhouse
gas. For the first time, a German-French research team showed which
methane
consuming microorganisms thrive in the ice-cold Arctic
deep-sea. In an article in the journal Nature,
the scientists also describe which environmental parameters control
their
activity - with a surprising result: High flow velocities of mud
volcano water
in the seafloor reduce the efficiency of the natural gas filter by 60
percent.
In
1990, the
Haakon Mosby mud volcano was discovered by an international research
team on
the continental slope of the Barents
Sea. The
scientists chose its name in honor of the famous Norwegian
oceanographer Haakon
Mosby. The mud volcano covers an area of a about 1 square kilometer and
is
located at a water depth of 1250 meters. The centre emits muds, water
and
methane that rise from a depth of about 2 kilometers below the mud
volcano.
Helge Niemann and Tina Lösekann from the Max Planck Institute
for Marine
Microbiology in Bremen,
Germany
investigated in their PhD thesis which
methanotrophic microorganisms could thrive in the -1°C cold Arctic
deep-sea.
Haakon
Mosby is a rather flat
mud volcano rising only 10 meters above the ocean floor. Visual
inspection by
the German and French researchers distinguished three distinct
concentric
ring-shaped zones: the centre, surrounded by a zone covered with sulfur
bacteria and then the outer rim inhabited by tubeworms.
Although
these habitats differ,
methane is the primary food source for most microorganisms thriving in
the
ocean floor. At the surface of the centre, the scientists discovered
formerly
unknown bacteria that use oxygen to feed on methane. In sediment layers
below
the sulfur bacteria, Helge Niemann and Tina Lösekann found a
new group of
methane-consuming Archaea that live in symbiosis with bacteria. This
community
does not use oxygen but sulfate to oxidize methane. This process is
called the
anaerobic oxidation of methane (AOM) and is investigated in the
research
project MUMM. To their surprise, the scientists discovered that the
majority of
methane is consumed in the tubeworm habitat and not in the center.
Why Methane Escapes
the Microbial Filter
With their
measurements, the scientists were
able to show that only 40% of the rising methane is consumed by
microorganisms.
This is less than in most methane-rich habitats. Until now, scientists
assumed
that higher fluxes of methane lead to greater numbers of methane
consuming
microorganisms. At Haakon Mosby, very little methane is consumed in the
gassy
centre of the mud volcano.
The marine biologist
Helge Niemann explains this
phenomenon: "The methane consuming microorganisms need oxygen or
sulfate
from the seawater to oxidize methane. In the mud volcano water that
flows
upwards through the ocean floor both compounds are missing. Since the
flow
velocity of this water is so high, very little oxygen and sulfate from
the
seawater can penetrate the ocean floor and therefore the microorganisms
in the
centre and bacteria mat zone just don’t get enough energy.
At the rim of the
volcano, the situation is very
different: Tubeworms grow about 60 cm deep into the seafloor and
actively pump
seawater into deeper layers. Microorganisms living at the roots of the
worms
profit from this situation. Here, Helge Niemann and Tina
Lösekann found the
highest consumption rates of methane indicating an efficient biological
filter
against the potential greenhouse gas methane.
Helge Niemann and
Tina Lösekann were supported
by a German-French research team who mapped the volcano with sonar and
video
systems and analyzed geochemical processes. The utilization of the
deep-water
robot Victor 6000 of the French research institute IFREMER, Brest
was crucial for the two highly
successful expeditions to the mud volcano with the research vessels
"L’Atalante" of IFREMER and "Polarstern" of the German
Alfred Wegener Institute.
Future Work
For the first time,
detailed surveys of element
fluxes and microbial consumption were carried out at a deep-sea mud
volcano in
the framework of the geotechnical project MUMM. It is now important to
examine
the efficiency of biological filters at other methane seeps. This
factor may be
relevant for the global climate but is until now poorly known.
The German-French
research team will therefore
continue the investigation of mud volcanoes. The next expedition with
the
German research vessel Meteor and the ROV Quest of Marum in Bremen
targets recently discovered methane seeps in the eastern Mediterranean.
In addition, further expeditions to the Haakon Mosby mud volcano are
planned in
the framework of the European research project HERMES.
##
Contact:
Dr.
Helge Niemann
Max-Planck-Gesellschaft
49-421-202-8653
hniemann@mpi-bremen.de
This
text derived from:
http://www.mpg.de/
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