快猫短视频

IN THE heart of Antarctica, nothing stirs. On the fringes of the continent
there are penguins, seals and birds a-plenty. But up on the great white plateau
of the interior, life has no foothold. Except, that is, in a vast hidden expanse
of freshwater the size of Lake Ontario. One of the world鈥檚 biggest lakes, it
lies beneath nearly 4 kilometres of ice, directly below the coldest spot on
Earth.

The water has been isolated from air and sunlight for up to 25 million years.
Biologists can hardly wait to probe its mysterious depths and discover what
strange organisms lurk within. Geologists and glaciologists are hot on their
heels. 鈥淓veryone is interested,鈥� says ice researcher Jean Robert Petit from the
Laboratory of Glaciology and Geophysics of the Environment in Grenoble. For two
years now, researchers round the world have been plotting ways to uncover the
lake鈥檚 secrets and, if they get their wish, the next few years will witness a
scientific feeding frenzy. 鈥淚t will be the decade of Lake Vostok,鈥� says
Petit.

The lake was named for the Russian research station that sits above its
southern edge鈥攁 place where in 1983 the temperature fell below 鈭�89掳C,
the coldest ever recorded on Earth. A huge smudgy crescent with a
surface area of around 14 000 square kilometres, Lake Vostok is more than 500
metres deep in places.

The first hints that water lay beneath the ice came from radio echo soundings
in the 1970s by Gordon Robin of the Scott Polar Research Institute in Cambridge.
Then, in 1993, satellite measurements of the ice surface found an area of ice
that was unusually flat鈥攎ore evidence for underlying water. When ice tries
to flow over rock, friction at its base crumples the surface into rough cracks
and ridges. On water, however, ice glides gracefully along and the surface stays
flat.

The satellite measurements put Lake Vostok on the map, but it was only in
1996 that researchers discovered the lake鈥檚 extraordinary size. That year,
glaciologist Martin Siegert of Bristol University was in Cambridge when Andrey
Kapitsa arrived from Moscow State University for a visit. Kapitsa had collected
seismic data from Vostok station back in the 1960s but had never checked it for
a lake. When he heard about the satellite data he decided to take another look
at his old records. Sure enough, the lake was there, and as Kapitsa, Siegert and
Robin sifted through the figures, Lake Vostok began to swell. The researchers
quickly realised that it was huge鈥攂y far the deepest subglacial lake ever
found. 鈥淭hat was major news,鈥� says Siegert. Suddenly, everyone wanted to
know.

Since then, Russian scientists headed by Valery Lukin of the Arctic and
Antarctic Research Institute in St Petersburg have made many more seismic
measurements. Not only did they confirm the lake鈥檚 depth and size, they also
found its bed was covered with thick layers of sediment鈥� an ancient record
of the lake鈥檚 past. Researchers began rubbing their hands.

One of their first questions was why the lake exists at all. Vostok is not
the only lake beneath the Antarctic ice sheet: Siegert has catalogued 77
scattered around the continent. Nobody understands why the lakes form where they
do, but researchers suspect the weight of the sheet above builds up until the
ice at the base melts.

However, Vostok鈥檚 sheer size sets it apart from the other lakes. 鈥淚f you took
all the ice and water off and let everything bounce up, it would still be a
deep, long valley,鈥� says Robin Bell, from Lamont-Doherty Earth Observatory in
New York. That, she says, suggests the lake was born from tectonic activity.
Lake Vostok lies on the flanks of the Gamburtsev mountains, a mighty range that
reaches up more than 3000 metres, yet still fails to pierce the surface of the
ice sheet (see Map).
Bereft of real rock samples to determine the age of
the mountains, researchers can鈥檛 tell how and why they formed. 鈥淭hey just stick
up under the middle of the ice sheet and no one knows what they鈥檙e doing there,鈥�
says Siegert.

Bell hopes that studying Lake Vostok and the area around it might yield some
answers. She wants to know if the forces that created both lake and mountains
are still at work today. The lake, she says, could be a cold, old rift basin
like Lake Superior鈥檚, a remnant of tectonic tearing that took place hundreds of
millions of years ago. Or the stretching could still be hot and active, like the
rift systems that created Lake Malawi and Lake Baikal. Working out
which鈥攊f either鈥攊s right matters to geologists, who are eager to
know if cold, ancient rock really does underlie East Antarctica, as they鈥檝e
always assumed. But it also has important implications for the nature of life in
the lake.

鈥淭he thing that will constrain life is the supply of carbon and energy,鈥� says
biologist David Karl from the University of Hawaii. And in the dark isolation of
the lake, both are likely to be scarce. Because of this, many biologists feel
that the likeliest inhabitants of the lake are bacteria. 鈥淭here鈥檚 not going to
be macrofauna鈥攖ardigrades or crustaceans,鈥� says Karl. 鈥淭he maintenance
metabolism that they need is just too high.鈥�

However, an additional source of energy could change all that. If Lake Vostok
is part of an active, wrenching rift system, its floor could be pitted with
hydrothermal vents. And in the deep ocean, such vents form oases for thriving
communities of strange, complex creatures. Even if the rift is old and cold, it
could still have a carbon source. If the lake existed before it was smothered by
ice, and supported a thriving ecosystem, carbon from long-dead organisms could
still be seeping slowly upwards out of the sediments that coat the lake鈥檚 floor.
鈥淭he microbes don鈥檛 care if it鈥檚 a hydrocarbon seep or a hot vent,鈥� says Karl.
鈥淚t鈥檚 all energy.鈥�

Without samples from the lake itself, there is no way to know what energy
sources and organisms Vostok harbours. And Bell points out that the lake might
not have come from tectonic activity at all: it might have been scoured out 25
million years ago when the ice sheet first ground over the continent. If so,
there would be no vents and no seeps. The lake鈥檚 only carbon would come from air
trapped in ice slowly making its way downwards.

Giant crystal

Wherever Vostok鈥檚 energy comes from, you need organisms to take advantage of
it. Throughout the lake鈥檚 history, microbes may have landed on the ice and
gradually worked their way down to seed the lake below. Though it is hard to be
sure without samples, some intriguing results are just emerging: the first
direct evidence of what the lake contains.

The results come from the world鈥檚 deepest ice core, completed last year at
Vostok station by a team of Russian and French scientists. The researchers
hauled up around 3620 metres of ice, but stopped 120 metres or so from the lake
surface to avoid contaminating it with drilling fluid. The core was drilled to
collect information about past climate. But as the team penetrated deeper and
deeper, they noticed something odd.

In the frigid heart of Antarctica, crystals of ice grow achingly slowly: at
鈥�55 掳C, 1 square millimetre of ice takes 10 000 years to form.
Consequently, crystals in the ice core tended to be just a few centimetres
across. But suddenly, 3540 metres down, the drillers began pulling up huge ice
crystals. 鈥淭here was one metre of core that was a single giant crystal,鈥� says
Petit, a member of the team. 鈥淚t was amazing.鈥�

Back in the lab, he and his colleagues confirmed their suspicions. The huge
crystals of ice must have formed in warmer conditions, in the balmy鈥攖hough
still subzero鈥攚aters of Lake Vostok itself. The team had collected lake
water frozen directly onto the base of the ice sheet.

Petit presented his findings to a workshop in Cambridge at the end of
September. So too did biologist John Priscu from Montana State University who
had studied a metre of lake ice from 3590 metres down, and Karl who had been
looking at a core from 3603 metres. Though neither knew the other was working on
the accreted ice, their results were very similar. Both found signs of microbial
life.

In electron micrographs, Priscu saw the bodies of tiny rod-like bacteria.
Karl鈥檚 microbes were viable鈥攖hey clearly respired and gave off CO₂.
Both researchers also found carbon in the cores, enough to suggest that
Lake Vostok has carbon stocks typical of temperate lakes and seawater. 鈥淭here鈥檚
food in the lake,鈥� says Priscu.

Though the two researchers found only simple microbes, Karl says this does
not rule out the possibility of more complex life near the lake floor. 鈥淭he
stuff down there might never make it up into the accreted ice,鈥� he says. 鈥淵ou鈥檝e
got 500 metres of water, and in the ocean 500 metres can be the difference
between life and death.鈥�

But even if the lake turns out to contain nothing but microbes, that would
still be an exciting prospect, says Karl. Isolated for perhaps millions of
years, the organisms might well have evolved unusual strategies to cope with the
extreme environment. Of all the Antarctic lakes, Vostok鈥檚 size makes it the one
most likely to have survived as a liquid throughout the history of the ice
sheet. 鈥淵ou would have the best chance there of developing adaptation strategies
to these unusual conditions,鈥� says Karl. 鈥淎nd smaller lakes are also more likely
to be homogeneous, which is not good for life.鈥�

While the geologists and biologists can鈥檛 wait to get their hands on real
samples from the lake, glaciologists like Siegert are cooler about the
prospects. 鈥淚鈥檓 not anti-Vostok,鈥� he says. But he points out that there are
plenty of other lakes that could be just as worthy of study, and are probably
easier to reach. One lies at the South Pole, which鈥攖hanks to the
well-established American base there鈥攊s virtually on the bus route.
Siegert is intrigued by the notion that lakes beneath the ice sheet may help to
lubricate its base, perhaps making it more susceptible to sliding into the
ocean, and he would like to study as many as possible. But he admits that Vostok
is unique as far as biologists are concerned, and is still eager to join the
feast.

Crown jewel

The next step will be to find a way to drill into the lake and see what鈥檚
really there. Frank Carsey, from NASA鈥檚 Jet Propulsion Laboratory in Pasadena
already has some ideas for how that could be done. Working with Hermann
Engelhardt at Caltech, who is an expert in using hot water to drill rapidly
through ice, Carsey has designed a cryobot鈥攁 robot about 3 metres long
which could melt through the ice sheet and explore the lake below.

NASA鈥檚 interest, he says, stems at least in part from the possible connection
with Europa, one of Jupiter鈥檚 icy moons. Researchers have found intriguing hints
that Europa鈥檚 surface crust of ice may conceal a vast liquid ocean
(鈥淲aterworld鈥�, 快猫短视频,18 September 1999, p 40).NASA
already has plans for a 2007 mission to Europa that will find out for sure. They
would love to drill through the ice and look for signs of alien life below, and
it鈥檚 no surprise that they are keen to practise their drilling technology on
Earth.

鈥淵ou have to get experience doing things under several kilometres of ice,鈥�
says Carsey. Radar expert Don Blankenship from the University of Texas at
Austin, who helped to draw up a list of potential science projects to fly on the
Europa mission, is also keen to practise picking out water and sediment layers
from his radar reflections. But he is nervous about using Lake Vostok as a
testbed for drilling. 鈥淟ake Vostok is the crown jewel of subglacial lakes in
Antarctica,鈥� he says. 鈥淚鈥檓 not sure we should learn to cut diamonds on the crown
jewels.鈥� Carsey agrees. 鈥淭he smart thing to do would be to build the Vostok
probe and try it out on something like an ice shelf,鈥� he says.

There are real fears that sampling the lake could also contaminate it.
Because of this danger, environmental groups are already campaigning to keep
Vostok undisturbed. However, the researchers argue that contamination could do
more damage to one of the smaller lakes. Vostok is so huge, they say, that a
small amount of foreign material wouldn鈥檛 make much difference to its overall
ecosystem. Moreover, they claim, science has a vested interest in preserving the
pristine conditions of the lake. 鈥淯nless we can keep it clean, there鈥檚 no
point,鈥� says biologist Mary Voytek from the US Geological Survey at Reston,
Virginia. 鈥淵ou don鈥檛 want to go in there and wreck your own laboratory.鈥�

And everybody ultimately wants to go in. Workshops to plan strategy have
already been held in St Petersburg, Washington DC and Cambridge. Another
workshop will be held next year to focus on drilling technology. Everyone is
hoping for a big international effort that will share both expertise and
logistics. 鈥淲e鈥檙e talking maybe five years for a large concentrated effort at
Lake Vostok,鈥� says Dennis Peacock from NSF鈥檚 headquarters in Washington DC.

Whatever the final details of the programme, researchers are convinced that
it will yield spectacular results. Take Karl, who in 1979 was one of the first
microbiologists to explore hydrothermal vents near the Galapagos islands. He
went to the site on a hunch, on the coat tails of geologists. And he and his
colleagues discovered something that took their breath away. 鈥淲e found organisms
that were harvesting geothermal energy, and that changed all the textbooks,鈥� he
says. 鈥淔or the first time we discovered that life on Earth is not dependent on
solar energy.鈥�

Karl says he now has the same kind of feeling about Lake Vostok. 鈥淲e don鈥檛
know what we鈥檒l find, but it may be some fundamentally different mode of life,鈥�
he says. 鈥淚f you go to unusual places, the chances are much higher of coming
back with something you really didn鈥檛 expect.鈥�