For the first time, submarine seeps gurgling natural gas from the
floor of Australia’s Timor Sea have been directly observed and
analysed, with surprising results.
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These shallow water seafloor seeps are about 160 kilometres south of
one of Australia’s largest oil and gas provinces, but have been
something of a mystery due to their remoteness. Dr Gregg Brunskill
of the Australian Institute of Marine Science (AIMS) said the
petroleum industry and Geoscience Australia had previously observed
bubble plumes at the sea surface in the Timor Sea but their
composition was unknown.
Dr Brunskill was the chief scientist on a major expedition aboard
the Marine National Research Facility RV Southern Surveyor
which set out to study the Oceanic Shoals, and communities that live
on and around natural gas seeps about 300 km north of Broome in seas
90 m deep.
Another task of the voyage was to collect sediment and coral cores
in deeper waters 300 km WNW of Darwin.
During the voyage, AIMS organic geochemist Dr. Kathy Burns
determined that the bubbles were virtually pure methane - 99%, laced
with other hydrocarbons - streaming from the seafloor 100 metres to
the surface.
"We estimate, in an area of half a square kilometre, up to a tonne
of methane per day is being dispersed into the atmosphere," Dr
Brunskill said.
"If these seeps occur throughout this continental shelf and slope
region, then that’s an enormous amount of gas entering the atmosphere
and contributing to the greenhouse effect and global warming."
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Methane vent tubes on the seafloor at Cornea Site. The vent tubes
are the pencil shaped objects in the upper centre, with slightly
reddish lips at the end >of the tube opening. These tubes are 10-15
cm long and 1-2 cm in diameter, and are composed of a very hard and
heavy mineral.
Photo: Max Rees
Methane bubble catcher
being deployed from a SS zodiac workboat at Cornea / Timor Sea
in early June 2005
Photo: Max Rees
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Dr Brunskill said methane is 20 times more powerful than CO2
as a heat trapping greenhouse gas, and natural fluxes of methane from
the ocean to the atmosphere are possibly significant in the natural
greenhouse gas budget.
With initial visions of children chasing bubbles at a party, the
idea of using a custom built "submarine bubble catcher" in the ocean
had the ship crew doubting the sanity of the scientists prior to its
deployment, but all were pleasantly surprised by the outcome. " The
bubble catcher device successfully measured the gas flux from the sea
to the atmosphere as 0.5 to 1 litre of methane per square metre per
day, but most of this happened during low tides," he said.
On board were collaborators from the Australian National University
(ANU), and AIMS based PhD students from the University of the Sunshine
Coast and from as far away as Brazil.
The Southern Surveyor provided these scientists with the
opportunity to deploy large & heavy sampling equipment, and to conduct
experiments that they are unable to do on smaller vessels. The Marine
National Research Facility also has modern equipment that allows
detailed mapping of the seafloor, and acoustic sounding of bottom
sediment structure below the seafloor.
Using AIMS underwater cameras and remotely operated submarine
vehicles, scientists were able to explore deep water biodiversity and
locate seafloor seep structures like domes and small gas vent tubes.
The first video footage of seafloor tube vents bubbling methane gas
has been captured revealing evidence that marine life is abundant
around the seep sites.
Dr Kathy Burns said samples of microbial life were taken, for
laboratory culture studies, to determine the ability of the organisms
to use methane and oily hydrocarbons as their energy source.
Scientists explored other deeper water mounds that rise 50 -100
metres from the seafloor 300 m below, collecting a ‘curious assemblage
of recent and fossil marine organisms’.
Even the geologists aboard the voyage were puzzled about fossil
sand dollars and sea urchins sitting right beside recently deceased or
living organisms. "We suspect the minerals associated with the seep
fluids cause a rapid fossilisation process," said Dr Gregg Brunskill.
Sediment cores taken from the Timor Sea region will be analysed at
AIMS and ANU, and will reveal the history of marine sedimentation and
oceanography during the last several centuries, and some longer cores
will expose a chronicle of ocean and climate variations over the last
10,000 to 20,000 years.
Coral cores were taken from large bommies on top of large mounds.
"Annual growth bands in the corals can be analysed for isotopes and
trace elements that tell us about the past history of seawater
temperature and salinity, and perhaps the rate of climate warming, "
Dr Brunskill concluded.
It is hoped a better understanding of how this region ticks, and
how oily hydrocarbons and methane influence marine life will
contribute to wise management of this resource rich region.
The Australian Institute of Marine Science and the Australian
National University in collaboration with Charles Darwin University,
and the Northern Territories government has joined forces to promote
research in the Timor and Arafura Sea. The new Arafura Timor Research
Facility (ATRF) was opened in June in Darwin.
