Re: Discovery of Antarctic subglacial rivers may challenge excavation plans


"Alan Johnson" <afjohnson@xxxxxxxxxxxxxxxxxx> skrev i en meddelelse
news:e34gl0$h9k$02$1@xxxxxxxxxxxxxxxxxxxx
Plans to drill deep beneath the frozen wastes of the Antarctic, to
investigate subglacial lakes where ancient life is thought to exist, may
have to be reviewed following a discovery by a British team led by UCL
(University College London) scientists at the Natural Environment Research
Council (NERC)Centre for Polar Observation and Modelling (CPOM).

In a Letter to Nature they report that rivers the size of the Thames have
been discovered which are moving water hundreds of miles under the ice.
The finding challenges the widely held assumption that the lakes evolved
in isolated conditions for several millions years and thus may support
microbial life that has evolved "independently". It has been suggested
that if microbes exist in the lakes, they could function in the same way
as those in the subsurface ocean of Jupiter's moon Europa or within
subsurface water pockets on Mars.

Professor Duncan Wingham, of UCL, Director of CPOM and who led the team,
says: "Previously, it was thought water moves underneath the ice by very
slow seepage. But this new data shows that, every so often, the lakes
beneath the ice pop off like champagne corks, releasing floods that travel
very long distances."

"A major concern has been that by drilling down to the lakes new microbes
would be introduced. Our data shows that any contamination will not be
limited to one lake, but will over time extend down the length of the
network of rivers. We had thought of these lakes as isolated biological
laboratories. Now we are going to have to think again."

The discovery, which came as a great surprise to the team, also raises the
possibility that large flood waters from deep within the interior may have
reached the ocean in the past and may do so again.

Subglacial lakes in Antarctica were first identified in the 1960s. Since
then over 150 have been discovered but it is thought thousands may exist,
as much of the bed of Antarctica remains un-surveyed. The team focused on
the Dome Concordia region in East Antarctica, where more than 40 lakes are
known to exist.

Ultra-precise measurements were taken using radars on the European Space
Agency ERS-2 satellite to examine in detail small changes in the surface
of some of the oldest, thickest ice in Antarctica. The satellite found
synchronous changes in the surface height separated by 290 kilometres.

The scientists argue that the only possible explanation of these changes
is that a large flow of water must have occurred beneath the ice from one
subglacial lake into several others. The finding re-invigorates old
speculations that Lake Vostok, which contains 5,400 cubic kilometres of
water (equivalent to London's water consumption over 5000 years), may have
generated huge floods that could reach the coast.

"The lakes are like a set of beads on a string, where the lakes are the
beads connected by a string or river of water," explains Professor
Wingham."

"For the most part, there is very little flow along the string. Then, one
of the lakes over pressurises and a flood occurs that fills the next
"bead" down the string. The lakes must be pressurising until the pressure
is high enough to force the water under the surrounding ice. Once it
starts to flow, it melts the ice, and there is a run-away effect."

"Whether that could start an immediate "chain reaction" down the string
(and hence to the coast), or whether that bead would "go off" sometime
later is a vital question to which we don't know the answer yet. But,
sooner or later, the system will be flushed throughout."

The outlet into the ocean shuld be accessible for submersibles or drilling
through shelf-ice - for closer scrutiny of the discharge.
It may have this sentiment of 'catastrophisme' that could make it a
geological 'darling' in the eye of the public (said the dull
sedimentologist)
I wonder what sort of sedimentary succession the release of such a major
volume of pressurized water would produce .. it would already be present at
the head of the outlet. I assume that they've got some idea of where the
outlet would be.

Carsten

Professor Martin Siegert, of the University of Bristol and a co-author of
the study, says: "Currently we don't know how full Lake Vostok is or the
length of time it will take to fill - it might be thousands or even tens
of thousands of years. Whether such a discharge could affect the ocean
circulation around Antarctica is an open question at this stage."

The study was funded by NERC and the ERS-2 satellite was funded by the
European Space Agency.

The story can be read at the University College London:
<http://www.ucl.ac.uk/media/library/subglacial>
__________

Regards

--
Alan Johnson, Geotr@ns
www.geotrans-online.de
German-English, Geosciences/Technical
http://geotransblog.blogspot.com/
Terminus Est




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