U.S. team drills through half-mile-thick sheet of ice to turn up cells

By Janet Raloff

Web edition: February 1, 2013
Print edition: March 9, 2013; Vol.183 #5 (p. 12)

Cells containing DNA have emerged as the first evidence of life in a subglacial lake in West Antarctica. On January 28, a U.S. research team retrieved water from Lake Whillans, which sits 800 meters below the ice surface. The water hosted a surprising bounty of living cells.

The scientists collected three 10-liter water samples from the lake. Preliminary tests conducted in mobile labs show that the cells are actively using oxygen. It may take months for biologists to identify the microbes present.

The microbes have been sealed off below the ice for at least 100,000 years.

A challenge was ruling out contamination as a source of the cells, says microbiologist Brent Christner of Louisiana State University in Baton Rouge, reached by satellite phone at a tent encampment at the drill site. Even glacial ice harbors low concentrations of microbes, “or their corpses,” so the researchers were concerned that cells in the lake samples could actually have come from the ice, Christner says.  

He argues that the cells come from the lake. First, cell concentrations in water retrieved from the lake were on the order of 10,000 per milliliter, which is about 100 times higher than the cell count in meltwater from the drill hole. Second, that meltwater is roughly comparable chemically to distilled water. In contrast, mineral levels in the water from which Christner’s team isolated its cells are 100 times higher — equivalent to what’s present in the lake’s water. 

“This is a big deal — and exciting,” says glaciologist Martin Siegert of the University of Bristol in England. The U.S. team’s drilling endeavor marks “the first clean access to a subglacial lake system.” Acquiring clean samples is imperative, he adds, to inspire confidence that any microbial finds truly come from the buried lakes.

Lake Whillans sits in a shallow cavity at the downstream end of a slow-moving sheet of ice. The deep liquid streams that feed this and more than 340 other subglacial lakes across Antarctica also lubricate the ice above. Geothermal energy, along with friction and a heavy blanket of ice, keeps the water liquid in this frigid land.

Excitement at the prospect of exploring the lakes erupted in 1996, recalls Siegert. That’s when an international research team he was part of realized the massive extent of Lake Vostok (SN: 6/29/96, p. 407), a subglacial lake discovered decades earlier. At once, Siegert says, microbiologists began proposing that this buried lake — and possibly others — might host ecosystems that had been cut off from the surface for a very long time.

Precisely how long remains unknown, says Slawek Tulaczyk, a glaciologist from the University of California, Santa Cruz, and a team leader on the Antarctic drill program. At Lake Whillans, “a good guess for a minimum is about 100,000 years.” That’s the last time the ice sheet may have shrunk back enough to expose the roughly 10-square-mile lake, he explains.

The new drilling project uncovered a second surprise: The lake is surprisingly shallow. Two years ago, a team conducted seismic experiments by detonating explosives; researchers used the resulting sound waves to map what lies beneath the ice. These seismic data indicated Lake Whillans was about 30 feet deep, Tulaczyk says. But instruments his team sent down the borehole now peg the lake’s depth “at only about 5 to 6 feet.”

The most likely explanation, Tulaczyk says, rests on a third surprise that emerged from the drilled borehole: The lake sediment contains a substantial amount of water. That unexpected mixing, he says, confused the earlier seismic readings.

Last year, a Russian team pierced Lake Vostok but has to date found no evidence of life. Last month, technical difficulties convinced Siegert and his colleagues on a British team to suspend their efforts for the year to reach the subglacial Lake Ellsworth (SN: 1/26/13, p. 9).

By January 31, the new 30-centimeter borehole down to Lake Whillans was beginning to freeze shut. So Tulaczyk’s group began lowering instruments down the hole one last time. This package will freeze in place until the researchers can return.