Stump the Scientist Scenes from AAAS Science After Hours

February 18, 2001

Uncovering Life in the "Valley of the Dead"
Rugged Antarctic researchers unveil a complex ecosystem of microbes in the ice cover of an Antarctic lake, and discover how the organisms' survival may depend on -- of all things -- dirt and bubbles.
by Mike Matz

At -30° Celsius, Priscu's team cuts into Antarctic ice, looking for signs of life.

Montana State biologist John Priscu probably gets a better workout doing his job than the average scientist does.

In temperatures that rarely topped -50° C, he and his colleagues recently spent three weeks using chainsaws (without oil) to slice deep into the thick ice cover of Bonney Lake in Antarctica. As the ice hole grew deeper, they had to use special blowers to expel the exhaust and supply fresh air to the fatigued saw handlers.

But the grueling labor paid off. Close inspection of Bonney's icy interior revealed both the presence of microbe colonies and important clues as to how these colonies survive -- discoveries that boost our rapidly expanding knowledge of Antarctic life in a place recently thought to be completely lifeless.

McMurdo Dry Valleys: An Alien Landscape

Bonney Lake is found in a desert region of Antarctica called the McMurdo Dry Valleys, the largest area of non-ice-covered land in Antarctica (about 4,000 square kilometers). But the region is also home to some of the world's only permanently ice-covered lakes, including Bonney. With an average air temperature of less than -20° C and annual precipitation of six centimeters, McMurdo is the coldest and driest desert on the planet.

Coated with a permanent ice cover, Bonney Lake is set in the bizarre landscape of Antarctica's McMurdo Dry Valleys.

In the early 1900s, when Antarctic explorer Robert Falcon Scott became the first man to hike through McMurdo, he referred to the region in his journals as the "valley of the dead." At the time, that must have felt like an apt description: there were no clearly visible signs of life in the region's otherworldly barren landscape of windswept rock and ice-capped lakes.

For many decades after Scott's expedition, no one offered evidence of life to challenge his eerie description of McMurdo.

But since 1990, pioneering Antarctic scientists have begun to find microbial life in McMurdo's soils, lakes, and ephemeral summer streams. John Priscu's team has been at the forefront of research looking for life inside the icy coating of the region's permanently ice-covered lakes.

Why look for life in ice? Ice can contain pockets of liquid water, which is a prerequisite for life. That means the interior of the ice is probably a wetter, warmer, and friendlier environment for life than the cold, dry surface of the McMurdo desert.

Searching for Life in Dirt

A scanning electron micrograph of microbes found in McMurdo Dry Valley lake ice.

For Priscu, a critical clue to the existence of life in the ice covers of McMurdo's lakes was the presence of sediment on their surfaces, deposited by fierce winds. Observing a dirty film of sediment on the lakes during the dark winter months but not in the light months, Priscu recognized that the dirt must seep into the ice as the sun melts the surface.

If microbes existed in the sinking sediments, they could potentially survive deep in the ice layer. The only way to find out was to extract samples from the ice.

Using a technique known as core sampling, which involves removing ice samples with a specially designed drill, Priscu's team found chunks of sediment trapped about two meters underneath the surface. Chemical and microscopic analysis of the samples indeed revealed a complex microbial ecosystem of many different species -- including photosynthetic microbes that make carbon from sunlight, and bacteria that live off the carbon. DNA studies showed that while most of these microbes seemed to be species found in the soil above, a few species had never before been documented by science.

Water and Bubbles

How did these sediment-bound creatures stay alive in the ice? Because life depends on the presence of liquid water, Priscu now needed to figure out how the microbes found water deep inside the ice cover. By collecting temperature data in the ice over time, Priscu's team discovered that as much as 35 percent of the ice was liquid in the areas where sediments were suspended.

That meant the sediment not only provided the microbes with nutrients and a free ride into the ice. It was also somehow helping them get water.

To follow up on these intriguing findings -- and explore the connections between the sediment, the microbes, and water -- Priscu decided to cut a giant chamber in Bonney's ice cover and expose the layer of sediment two meters down. That's where the chainsaws and the back-straining three weeks came in.

The ice cavern, which was more than three meters deep when completed, unveiled stunning bubble patterns on the walls.

"All the work did pay off," Priscu said. "We could now look around the sides and get the big-picture view of what's going on."

What they saw inside the cavern was an awe-inspiring gift from nature: covering the icy walls were beautiful spraying patterns of bubbles fanning above clusters of sediment.

The bubbles were not only elegant; they also painted critical insights into the survival of life in Lake Bonney. Since bubbles form as liquid water freezes, their presence offers more evidence that the sediment clusters were in liquid at one point.

Deeper analysis of the bubble shapes and spray patterns show that the clusters were the last place to freeze. This may partly be because the bubbles seem to act as "light pipes" for the sediment. Preliminary light studies in Priscu's laboratory reveal that the peculiar arrangement of bubbles seems to focus sunlight onto the sediment below, providing more light for photosynthesis and more heat to maintain a liquid environment longer.


Elegant spraying patterns of bubbles in these lake-ice blocks offer clues to how microbes in the sediment clusters survive deep in the ice.

Beyond Bonney

The microbiological discoveries of Antarctic scientists like Priscu may open scientific doors far beyond the realm of Antarctica.

For one, the landscape of the McMurdo Dry Valleys is perhaps earth's closest analogue to the ice-covered surface of Jupiter's moon Europa. Antarctic researchers, for example, have noted that the visually chaotic appearance of the ice surface on McMurdo's permanently ice-covered lakes is very similar to what scientists think Europa's ice looks like.

Because of these similarities, better understanding lakes such as Bonney can provide important insights for astronomers as they seek to uncover the geological and chemical -- and possibly even the biological -- characteristics of Europa. Our earthly research can also help us design the tools and technology we'll need to explore this faraway moon's surface.

Life in McMurdo may also hold secrets to the origins of life on earth. While some researchers believe the first organisms arose out of a hot soup, many Antarctic scientists are looking for clues pointing to the origins of life when earth was blanketed by ice, about 600 million years ago. During this ancient freeze -- like in present-day Antarctica -- life was more likely to exist and evolve in the interior of the ice than on the harsh surface.

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