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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."
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.
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