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
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,
"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."
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).
"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.