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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