Back in 1974, a survey aircraft flying over central Antarctica and beaming radio waves down at the ice detected a peculiar signal--a signal of liquid water trapped under the two-and-half-mile-thick ice sheet. The radio pulse reflected not only off the ice surface but off the base of the ice, and that’s how we found the signature of an ice-water contact, says glaciologist Martin Siegert of the University of Wales. This past year, with the help of satellite surveys and seismic measurements, Siegert and his colleagues determined just how much water is trapped under the polar ice cap. They found an expanse the size of Lake Ontario, more than 5,000 square miles in area and at least 1,600 feet deep.
The glacier acts as a blanket, explains Siegert, keeping the bottom insulated from the extreme cold at the surface. Geothermal heat from below and pressure from the ice above melts the bottom ice, and a stable melting cycle is maintained. Water collects in bedrock pockets, and over millennia forms a lake. The lake may even be inhabited by microbes-- sediments deposited on the lake bottom by the glacier as it grinds over the bedrock would be a possible source of nutrients. If so, the microbes are likely to be strange and interesting ones. It’s been a closed system for more than 2 million years, says Siegert. Anything that has evolved in this lake will be totally alien to what we know on the surface.