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Discovery of Antarctic subglacial rivers may challenge excavation plans

20.04.2006


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."

Judith Moore | EurekAlert!
Further information:
http://www.ucl.ac.uk

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