CHAPEL HILL - Some 15 feet under windswept lake ice in Antarctica -- the world's most inhospitable landscape -- scientists have discovered teeming microbe colonies that use sunlight filtering through the ice to activate and sustain life when the South Pole tilts toward the sun each year.
In fact, the researchers have found surprisingly diverse microorganisms throughout the frozen lake water, supported by the key life-sustaining processes photosynthesis and atmospheric nitrogen fixation. Previously, most investigators thought little or no biological activity could occur within the ice itself.
"This discovery, which is quite exciting, shows how life could exist on other planets," said Dr. Hans Paerl, Kenan professor of marine sciences at the University of North Carolina at Chapel Hill. "Solar heating allows the water to melt around soil particles that have blown over the ice and have been buried in it. Microbes covering them can then spring to life within an hour under certain conditions, even though they are still embedded deep in the ice."
The result, Paerl said, are living layers within the ice that distinctly show years, like growth rings in a tree trunk. He called the layers "self-sustaining microbial ecosystems."
"A key to the ability of microbes to live under these extreme conditions is the presence of liquid water, which is formed by solar heating of dark, light-absorbing soil aggregates embedded in the ice," he said.
A report on the findings appears in the June 26 issue of Science. Besides Paerl, report authors include John C. Priscu of Montana State University; Stephen J. Giovannoni of Oregon State University, Christopher P. McKay of NASA Ames Research Center in Moffet Field, Ca. and James L. Pinckney of UNC-CH.
Soil particles carried by wind from dry Antarctic valley floors onto the frozen lakes absorb sunlight during summer in the Southern Hemisphere, warm up and slowly melt down through the thick ice, the new studies showed. After descending through the ice, they break through and fall to the lake floor.
"We think this work suggests that even though the ambient temperatures on other planets are quite low, soil particles could heat up enough locally through solar heating to support formation of liquid water, microbial growth and reproduction," Paerl said. "Mars is a good example of the kind of place where this might happen."
Among the microbes the scientists identified were blue-green algae, or cyanobacteria, which are the most ancient photosynthetic, oxygen-producing organisms known on Earth, and various bacteria, the marine scientist said. During months of total darkness, the microscopic worlds of soil, melted water and microbes within the ice freeze completely again to wait for the sun the following year.
In an accompanying editorial, Roland Psenner and Birgit Sattler of Innsbruck University say because of the new discovery, cultivating bacteria and algae in a deep freeze is not so outrageous an idea as previously believed.
"What at the first glance appears to be a contradiction in terms (being frozen and leading an active life at the same time) turns out to be an exciting example of the adaptation of microorganisms to environmental extremes," they wrote.
"What is the attraction of studying life in the cold? It may be the beauty of simplicity, which-especially in the case of the Antarctic lake ice-promises that sooner or later we may be able to understand and model ecosystems with simple structures and frozen dynamics."
The research team carried out its experiments at Lake Bonney in the Antarctic McMurdo Dry Valleys.
Materials provided by University Of North Carolina At Chapel Hill. Note: Content may be edited for style and length.
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