Frigid water is seeping into and out of a vast lake beneath 4 kilometers of ice in Antarctica. The newly unveiled circulation isn't quite as vigorous as the flow in your neighborhood pool, but it may supply fresh food to a suspected population of microbes in the lake.
The icy lake, called Lake Vostok, lies under Russia's Vostok Station in central Antarctica. It sits within a wide chasm where the Antarctic continent is drawn apart by tectonic forces. Warmth from the Earth has melted about 2000 cubic kilometers of water, making Lake Vostok by far the largest of more than 70 known lakes within the Antarctic ice. Researchers speculate that primitive life could eke out an existence there, subsisting on a bare minimum of dissolved organic carbon--a notion bolstered by the recent discovery of bacteria within refrozen ice in a core drilled to 100 meters above the lake under Vostok Station (ScienceNOW, 9 December 1999).
Now, a study in the 10 February Nature reveals that water, and potentially water-borne nutrients, cycle through the lake more quickly than expected. A team led by glaciologist Martin Siegert of the University of Bristol, United Kingdom, analyzed radar images of ice layers above Lake Vostok. The thickness and relative spacing of these strata shows how the ice has built up or melted with time. The team also used satellite images to track the motions of the Antarctic ice sheet across the lake's surface. Taken together, the data show that nearly 10 centimeters of ice melt each year at one end of the lake. The melting occurs where the overlying ice is about 400 meters thicker, Siegert notes; the added pressure lowers the melting temperature, just as the pressure of an ice skater's blade creates a thin rind of water underneath. Meanwhile, water refreezes at the other end, beneath Vostok Station.
The resulting rate of water exchange is perhaps 10 times faster than previously thought. "It's likely to induce turbulence throughout the entire volume of the lake," Siegert says. The cycling may replace the lake's water every 50,000 to 100,000 years, although the lake itself probably has existed for tens of millions of years.
The research is good news for those who long to find isolated ecosystems in Lake Vostok's dark waters, says glaciologist Charles Bentley of the University of Wisconsin, Madison. Freshly melted ice should infuse the lake with oxygen, carbon dioxide, and other nutrients. However, Bentley notes that it is not yet clear how far into the deep lake these nutrients might penetrate.