Berkeley - Measurements of the ice temperature far below the South Pole suggest that a so-called "lake" discovered at the base of the ice is most likely permafrost - a frozen mixture of dirt and ice - because the temperature is too low for liquid water. Far from being a disappointment, says a University of California, Berkeley physicist, the permafrost subglacial lake may be ideal for developing and testing sterile drilling techniques needed before scientists attempt to punch through the ice into pristine liquid lakes elsewhere in Antarctica in search of exotic microbes.
Techniques that avoid contaminating a drill site with microbes also would prove useful for future drilling into Mars' polar caps in search of life.
"This would be an excellent place to develop a sterile drill," said P. Buford Price, professor of physics at UC Berkeley. "Then, if we find that we've inadvertently contaminated the permafrost lake, we can be confident that the contamination is confined to only a small area."
Drilling into a frozen lake 2.8 kilometers below South Pole Station would have scientific interest in its own right, he said.
"We are likely to find interesting microbial life in the permafrost, in addition to learning how to drill in a sterile way," he said.
Price and colleagues in the United States and Russia made the recommendation in a paper that appeared in the June 11 issue of the Proceedings of the National Academy of Sciences. In their paper, the team reported data on temperature versus depth down to 2.3 kilometers beneath South Pole Station, based on temperature sensors implanted as part of the Antarctic Muon and Neutrino Detector Array (AMANDA) observatory.
Price, a cosmic ray physicist, is one of more than 100 collaborators in the AMANDA project, a National Science Foundation-funded array of detectors imbedded in deep ice at the South Pole and primed to look for high-energy neutrinos originating in exotic objects outside our solar system, such as black holes or the active centers of distant galaxies. AMANDA will become part of a larger, kilometer-scale neutrino observatory named IceCube, for which funding by NSF began earlier this year.
Based on measurements down to 2.3 kilometers, the team estimated the temperature at the bottom of the ice, 2.8 kilometers below the surface. This temperature - 9 degrees below zero Celsius (about 15 degrees Fahrenheit) - is 7 degrees colder than the temperature at which ice melts under the pressure of nearly 3 kilometers of ice.
Several years ago, radar images of the ice around the South Pole showed evidence of a subglacial lake about 10 kilometers from the pole. Price said that the temperature there should be about the same as the temperature at the AMANDA site, meaning that the under-ice lake would likely be a frozen mixture of ice and sediment in order to explain the flat terrain indicated by radar images. The permafrost, similar to that found in Arctic regions of North America and Europe, may be 10 or 20 million years old, dating from before the Antarctic continent was covered by a sheet of ice.
Since any contamination introduced by drilling into the permafrost would not travel far, the site would make a good place to test such techniques in preparation for drilling into Lake Vostok, a huge, Lake Ontario-sized subglacial sea that has intrigued scientists since it was detected four kilometers below the ice in 1996.
Proposals to drill into Lake Vostok have met with opposition because of the danger of contamination. In addition, many of the nearly 100 under-ice seas discovered to date may be interconnected, so contaminating one could contaminate them all. An international committee is discussing the issue, which may delay drilling for a decade.
Drilling first at the site near the South Pole also would be more convenient, because there currently are no permanent facilities near Antarctica's subglacial lakes comparable to South Pole Station.
As part of the AMANDA and IceCube projects, temperature gauges were installed in bore holes that had been drilled with hot water down to 2,345 meters, nearly to the base of the ice at 2,810 meters at the South Pole. The gauges provided a detailed profile of temperature under the surface and also allowed Price and his colleagues to predict the temperature at the base of the ice: -9ºC
Price is primarily interested in the kinds of exotic microbes that might live inside solid ice, either as dormant spores or at a low level of activity. He said that life has been found wherever people have looked, from deep in the Earth's crust to high-altitude clouds, and he thinks they also reside deep inside glacial ice. In fact, he will present a poster on life in solid ice at the Bioastronomy 2002 meeting in Australia during the week of July 8.
Such creatures would not live in ice crystals, but in interconnected liquid veins at the boundaries where ice crystals meet.
"Even at temperatures far below the freezing point, there is always some liquid," he said. "As water freezes, soluble salts and acids are excluded from the interiors of the freezing crystals, creating a network of thin liquid veins rich in nutrients for energy and elements such as carbon necessary for building more microbes. Bacteria are small enough to fit and move inside the veins. Why wouldn't bacteria take advantage of that? Well, they probably do."
He and UC Berkeley colleagues have developed instruments that they have lowered into boreholes in Greenland and Antarctic ice to search for microbial life. The devices flash ultraviolet light, and detectors record any telltale fluorescence from bacteria. Such fluorescence is faint, however, and the team is still perfecting the instrument.
In a second approach, Price and his colleagues have built at UC Berkeley a refrigerated box in which they can investigate sections of ice cores from Antarctica and Greenland in search of exotic, deep-ice bacteria new to science. With a fluorescence microscope mounted inside the cold box, they can search for the faint light emitted by fluorescing bacteria.
"With the refrigerated microscope, we can catch any microbes trapped in liquid veins in their icy habitats," Price said. "This greatly reduces the possibility of contamination. If we just looked in melted ice, we wouldn't know where the bacteria had come from."
Price laid out his reasons for looking in frozen ice for unusual microbes in a paper in the February 1, 2000, issue of PNAS. He argued that ice-loving bacteria, or psychrophiles, could easily live in interconnecting veins of liquid water formed where three ice crystals intersect. Such microbes could survive for hundreds of thousands of years at a temperature just below freezing, metabolizing but probably not multiplying. They would have to endure darkness, 400 times the pressure at the surface, no oxygen, a starvation diet and probably a highly acidic or salty environment.
He estimated that colder ice as old as 400,000 years could still support one cell per cubic centimeter.
Drilling in Antarctic ice, including to within about 100 meters of Lake Vostok, has turned up some bacteria, according to Russian scientists, but all were known before. Bacteria also have been found in ocean ice. Price and other scientists hope to discover new species in solid ice, analogous to the novel thermophiles found in hot seafloor vents living at temperatures above the sea-level boiling point of water (100ºC or 212ºF).
All this makes it essential that drills not introduce bacteria into a new environment, whether a sub-glacial lake isolated for half a million years or the ice caps of Mars. No sterile drilling has ever been achieved, Price said, though some drilling under "aseptic" conditions has been claimed. Even the sterilization procedure taken before sending the Voyager spacecraft to Mars were, in retrospect, insufficient to kill many microbes discovered in the intervening 25 years.
"If microbes can exist in glacial ice on Earth, they can also exist in Martian permafrost and in certain regions of Jupiter's ice-covered moons," he said.
Price's colleagues on the recent PNAS paper are Oleg V. Nagornov of the Moscow Engineering Physics Institute; Ryan Bay, Dmitry Chirkin, Predrag Miocinovic and Kurt Woschnagg of UC Berkeley; Yudong He of Rosetta Inpharmatics in Kirkland, Wash.; Austin Richards of Indigo Systems Corporation in Santa Barbara, Calif.; Bruce Koci of the Space Sciences and Engineering Laboratory at the University of Wisconsin, Madison; and Victor Zagorodnov of the Byrd Polar Research Center at Ohio State University in Columbus.
Materials provided by University Of California - Berkeley. Note: Content may be edited for style and length.
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