ERS-2 helps detect massive rivers
under Antarctica
European Space Agency
British scientists have discovered rivers the size of the
Thames in London flowing hundreds of miles under
the Antarctica ice shelf by examining small changes
in elevation, observed by ESA’s ERS-2 satellite,
in the surface of the oldest, thickest ice in
the region, according to an article published
in Nature this week.
The finding, which came as a great surprise to
the scientists, challenges the widely held assumption
that subglacial lakes evolved in isolated conditions
for several millions of years and raises the possibility
that large floods of water from deep within the
ice’s interior may have generated huge floods
that reached the ocean in the past and may do
so again.
Prof. Duncan Wingham, of the University College London, who
led the team said: "Previously, it was thought that
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."
The team found anomalies in the ice-sheet surface elevation
using ultra-precise measurements from ERS-2’s radar altimetry
and radar interferometry. Close inspection of one anomaly
revealed an abrupt fall in ice-surface elevation with a corresponding
abrupt rise some 290 kilometres away. The scientists state
the only possible explanation for these changes is that a
large flow of water was transferred beneath the ice from one
subglacial lake into several others.
Radar altimeters – originally designed to measure the
sea surface height by sending 1800 separate radar pulses down
to Earth per second then recording how long their echoes take
to bounce back – have been highly successful in measuring
large-scale ice surface changes over time. Radar interferometry,
known as InSAR, is used to precisely measure the spatial pattern
of the changes. Together, they form a powerful 'instrument'
to investigate the physical causes of changes in the ice surface.
According to Prof. Wingham, Director of the Centre for Polar
Observation and Modelling (CPOM), both sensors were essential
for the study. "With radar altimetry we can tell how
much the lake levels fell and rose, and that it occurred between
late 1996 and early 1998, but we cannot determine the area,
which is vital for investigating the physics of the flood
because we need to know the volume of water involved.
"Hence we turned to ERS-2 InSAR interferometry, which
has excellent spatial resolution. With it, we were able to
image the area of at least part of one lake, which was enough
to give us an idea of the volume, and with this we could get
at the rate of the flow."
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 unexamined. The team focused its study on the Dome
Concordia region in East Antarctica, where more than 40 lakes
are known to be.
Several groups, under the umbrella of the Scientific Committee
on Antarctic Research (SCAR), are currently investigating
the prospect of drilling down to subglacial Antarctic lakes
where ancient life is thought to exist. However, in light
of this discovery, these plans may need to be reviewed.
"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," Prof. Wingham
said.
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