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Lukin said Russia had waited for several years for international approval of its drilling technology before proceeding to reach the lake. He said about 1.5 cubic meters (50 cubic feet) of kerosene and freon poured up to the surface tanks from the boreshaft, proof that the lake water streamed up from underneath, froze and then blocked the hole, sealing off the chance that any toxic chemicals could contaminate.

Russian scientists will later remove the frozen sample for analysis in December when the next Antarctic summer season comes. They reached the lake just before they had to leave at the end of the Antarctic summer, as plunging temperatures halted air links.

Some scientists hope that studies of Lake Vostok and other subglacial lakes will advance knowledge of Earth’s own climate and help predict its changes.

“It is an important milestone that has been completed and a major achievement for the Russians because they’ve been working on this for years,” said Professor Martin Siegert, a leading scientist with the British Antarctic Survey, which is trying to reach another Antarctic subglacial lake, Lake Ellsworth.

“The Russian team share our mission to understand subglacial lake environments and we look forward to developing collaborations with their scientists and also those from the U.S. and other nations, as we all embark on a quest to comprehend these pristine, extreme environments,” he said in an email.

Americans scientists are drilling at Lake Whillans, west of the South Pole.

In the future, Russian researchers plan to explore the lake using an underwater robot equipped with video cameras that would collect water samples and sediments from the bottom of the lake, a project still awaiting the approval of the Antarctic Treaty organization.

The prospect of lakes hidden under Antarctic ice was first put forward by Russian scientist and anarchist revolutionary, Prince Pyotr Kropotkin, at the end of the 19th century. Russian geographer Andrei Kapitsa noted the likely location of the lake and named it following Soviet Antarctic missions in the 1950s and 1960s, but it wasn’t until 1994 that its existence was proven by Russian and British scientists.

The drilling in the area began in 1989 and dragged on slowly due to funding shortages, equipment breakdowns, environmental concerns and severe cold.

The lake’s pristine water may make entrepreneurs sweat just thinking of its commercial potential, but Lukin shot that idea right down.

He said his team had no intention of selling any Vostok water samples but would eventually share the results of their work with scientists from other nations.

AP science writer Seth Borenstein contributed to this report from Washington.