Antarctic Lakes: 145 and Counting, Scientists Say
for National Geographic News
|November 1, 2004|
Don't don your swim trunks just yet, but deep beneath the Antarctic ice
sheets are at least 145 lakes that may be teeming with microscopic
organisms similar to those that could be thriving beneath the ice on
Jupiter's moon Europa, according to scientists.
The lakes lie beneath blankets of ice up to 2.5 miles (4 kilometers) thick and are considered one of the great unexplored frontiers on Earth.
Scientists are engaged in a long-term program to understand what type of life may survive in the lake water, sediments below, and ice above. Current efforts are focused on the ice above, which includes lake water frozen to the ice sheet bottom, known as accreted ice.
"The glacial ice should provide the biological seed for the lakes and the accretion ice should reveal actual genomes within the lake itself," John Priscu, an ecologist with the department of land resources and environmental sciences at Montana State University in Bozeman, said in an email from the Antarctic.
Martin Siegert, a glaciologist in the school of geographical sciences at the University of Bristol in the United Kingdom, said scientists first recognized the existence of the lakes in 1970. The most recent inventory, to be presented at the December meeting of the American Geophysical Union in San Francisco, California, puts the number of known lakes at 145.
"This is not the total number that will be found there. There are large regions yet to be surveyed comprehensively and the only way this number is going to go is upwards. I would estimate there are 300, 400, maybe 500 lakes," he said.
According to Priscu, the west Antarctic is particularly intriguing. "It is beginning to sound like a complex hydrological system, complete with continental size river basins like the Mississippi," he said.
Antarctic researchers identify the presence of lakes beneath the miles-thick Antarctic ice using a technology known as radio echo sounding, which works in the same manner as radar used to detect aircraft flying high in the skies.
"High-frequency radio waves at an airport fired up into the air bounce off anything with a change in the electric properties of the medium," Siegert said. "In the case of an aircraft, there are differences in the electrical properties of the air and the metal of the aircraft."
Radio waves also travel easily through ice sheets. So researchers began flying over the Antarctic in the 1970s firing radar down into the ice sheets, noting changes in electrical properties when the waves bounced off what lay beneath the ice.
In a few places the type of reflection the researchers received were distinctvery strong, bright, and extremely flat. "Smooth, flat regions at the base of ice sheets are very unusual compared to the more normal rocky beds," Siegert said.
The researchers performed some calculations and came to the conclusion that the only thing that could give such reflection is an ice-water interface, leading to the hypothesis that what the researchers were seeing in the radar soundings were indeed lakes.
Then, in 1996, Russian and British scientists reported on seismic soundings at what appeared to be a huge lake under Russia's Vostok Station. Seismic waves, unlike radio waves, give a profile of water depth. The results showed a water depth in one place of 1,640 feet (500 meters).
Further measurements of the lake, known as Lake Vostok, place it among the largest in the world; comparable in size and depth to North America's Great Lakes. Vostok is thought to be 30 miles (48 kilometers) wide by 140 miles (225 kilometers) long and reaching a maximum depth of 3,000 feet (914 meters).
But why aren't the lakes frozen?
"Three delicately balanced physical properties merge beneath the ice sheet to form liquid water," Priscu said. "Reduced freezing point, Earth's heat flux, and the thermal blanket formed by the 2.5 mile thick ice sheet."
Pressure from the miles-thick ice actually reduces the freezing point to 30 degrees Fahrenheit (-1 degree Celsius). Water normally freezes at 32 degrees Fahrenheit (0 degrees Celsius).
In addition, the ice sheet acts like a huge blanket that locks in the geothermal heat naturally radiated from Earth.
"It is enough heat to cause the base of the ice sheet to be at the melting point provided the ice is thick enough to insulate it from the cold surface," Siegert said. Surface temperatures routinely drop below -58 degrees Fahrenheit (- 50 degrees Celsius).
Scientists believe these so-called sub-glacial lakes began to form after Antarctica separated from the super-continent known as Gondwanaland and was surrounded by the circumpolar current.
"The current blocked heat flux to the polar region, making it cold," Priscu said. "Glaciation started perhaps 30 million years ago in the Antarctic in the mountains and eventually covered the entire continent."
While evidence suggests the ice sheet has come and gone in the west Antarctic, some scientists believe the east Antarctic ice sheet has been in place for at least 15 million years, Siegert said.
If the east Antarctic lakes have been under ice for millions of years, their waters and surface sediments have been isolated from the atmosphere for millions of years. Any life that may exist there does so in the absence of sunlight and must feed on chemicals.
Scientists are eager to sample the lake water and sediments to see if indeed life does thrive there, in part because images of Jupiter's moon Europa suggest it may contain an ice covered liquid ocean.
"There's no sunlight getting down to that water, so the type of life in Vostok and how it functions may be very relevant to Europa," Siegert said.
As part of the long-term plan to sample Vostok waters, Siegert is leading an international effort to explore Lake Ellsworth, a sub-glacial lake in the west Antarctic. The team could sample the Ellsworth waters by the end of the decade.
Priscu's efforts are focused on the ice. "My lab is currently trying to figure out if there is actual metabolism within the ice itself. If so, the entire ice sheet may be alive," he said.
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