The Russian project, at Lake Vostok, breached its surface last February after a decade of struggling to get through more than two miles of ice to water that had been sealed away for millions of years. That was at the very end of the Antarctic field season, and weather at Vostok, the site of the coldest temperature ever recorded on Earth (minus 128.6 Fahrenheit), forced a quick departure.

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The Russians are back at Lake Vostok this year to retrieve samples of the water that flowed from the surface of the lake up the drill’s bore hole, but they will not know what they have until they return with it to Russia for analysis there. One limitation of the project is that the samples are from only one spot on the surface of a body of water that is the size of Lake Ontario.

The British project also intended to retrieve water samples for later studies, from another, smaller body of water, Lake Ellsworth. But researchers called off that attempt on Christmas Day because the drilling process ran into difficulty at about a thousand feet. The water they had hoped to reach lay almost two miles deep.

The American project is different in several ways. Lake Whillans is smaller and not as deep, and is replenished more quickly from other water sources under the Antarctic ice shelf. It is a basin in a subglacial river where water accumulates to form a lake but keeps flowing, eventually reaching the ocean.

Dr. Priscu said that while the water in Lake Vostok was replaced about every 10,000 years, and the water in Lake Ellsworth every 700 years or so, the replacement rate for Lake Whillans was more on the order of a decade.

The scientific approach is different as well. The Wissard project involves the use of a remote torpedo-shaped submersible, about two and a half feet long. It will operate on a tether about a mile long and will be used to map the three-dimensional space of the underground lake, including its inlets and outlets. Dr. Tulaczyk said that understanding the shape of the lake, and how the water moves in and out, is important for knowing how and why the glaciers above these deep lakes move, “why parts of Antarctica are gaining, and others losing” ice cover.