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An unmapped reservoir of briny liquid chemically similar
to sea water, but buried under an inland Antarctic glacier,
appears to support unusual microbial life in a place where
cold, darkness and lack of oxygen would previously have
led scientists to believe nothing could survive, according
to newly published research.
After sampling and analyzing the outflow from below the
Taylor Glacier, an outlet glacier of the East Antarctic
Ice Sheet in the otherwise ice-free McMurdo Dry Valleys
of Antarctica, researchers believe that, lacking enough
light to make food through photosynthesis, the microbes
have adapted over the past 1.5 million years to manipulate
sulfur and iron compounds to survive.
The microbes also are remarkably similar in nature to
species found in marine environments, leading to the conclusion
that the populations under the glacier are the remnants
of a larger population of microbes that once occupied
a fjord or sea that received sunlight. Many of these marine
lineages likely declined, while others adapted to the
changing conditions when the Taylor Glacier advanced,
sealing off the system under a thick ice cap.
The research answers some questions and raises others
about the persistence of life in extreme environments
such as under glaciers, or even in liquid lakes trapped
kilometers under the Antarctic ice sheet, environments
that until recently scientists would not have believed
could support living creatures.
"Among the big questions here are ‘how does
an ecosystem function below glaciers?', ‘How are
they able to persist below hundreds of meters of ice and
live in permanently cold and dark conditions for extended
periods of time, in the case of Blood Falls, over millions
of years?," said Jill Mikucki, the lead author on
the paper.
Mikucki is a National Science Foundation-funded researcher
at Dartmouth College in the Department of Earth Sciences
and a Visiting Fellow at the Dickey Center for International
Understanding and its Institute of Arctic Studies.
The Dry Valleys are completely devoid of animals and
complex plants and scientists consider them to be one
of the Earth's most extreme deserts. The Valleys receive,
on average, only 10 cm (3.93 inches) of snow each year.
Despite the lack of precipitation, during the Antarctic
summer, temperatures rise just enough for glaciers protruding
into the valleys to begin melting. The meltwater forms
streams that enter lakes covered by ice that is two to
three stories thick.
Mikucki and her colleagues based their analysis on samples
taken at the ominously, but aptly named Blood Falls, a
water-fall-like feature at the edge of the glacier that
flows irregularly, but often has a strikingly bright red
appearance in stark contrast to the icy background.
The Dry Valleys have been the target of scientific inquiry
since the early days of Antarctic exploration in the so-called
"Heroic Age" early in the 20th Century. Even
the earliest explorers noted the massive stain at the
snout of the glacier and speculated as to what may have
caused it.
"The original explorers," Mikucki said, "thought
that red alga was responsible for the bright color."
More than a century later, the Dry Valleys remain a source
of immense scientific curiosity. One of NSF's Long-Term
Ecological Research projects network of 26 sites worldwide
is located there. And, as part of its research program
during the International Polar Year (IPY), NSF supported
an extended research season in the Dry Valleys, allowing
scientists for the first time to stay in the field as
six months of darkness descended to study how the microscopic
creatures there reacted.
NSF administers the U.S. Antarctic Program and was the
lead U.S. agency for IPY.
In the paper, however, Mikucki and her colleagues argue
that the creatures that survive under the Taylor Glacier
are both far more exotic and far more adaptable than the
early explorers thought.
Because the outflow from the glacier follows no clear
pattern, it took a number of years to obtain the samples
needed to conduct an analysis. Finally she obtained a
sample of an extremely salty and clear liquid for analysis.
"When I started running the chemical analysis on
it, there was no oxygen," she said. "That was
this when got really interesting, it was a real 'eureka'
moment."
Further genetic analysis suggests that of the relatively
small numbers of microorganisms found in the brine, "the
majority of these organisms are from marine lineages,"
she said.
In other words, microorganisms more similar to those
found in an ocean than on land, but capable of surviving
without the food and light sources available in the open
ocean.
"The salts associated with these features are marine
salts, and given the history of marine water in the dry
valleys, it made sense that subglacial microbial communities
might retain some of their marine heritage," she
added.
This led to the conclusion that the ancestors of the
microbes beneath the Taylor Glacier probably lived in
the ocean many millions of years ago. When the floor of
the Valleys arose more than 1.5 million years ago, a pool
of seawater from the fjord that penetrated the area was
trapped. The pool was eventually capped by the flow of
the glacier.
The briny pond, whatever it's size "is a unique
sort of time capsule from a period in Earth's history,"
Mikucki said. " I don't know of another environment
quite like this on Earth."
Life below the Taylor Glacier may help scientist address
questions about life on "Snowball Earth", the
period of geological time when large ice sheets covered
the Earth's surface. But it's also a rich laboratory for
studying life in other hostile environments, including
the subglacial lakes of Antarctica and perhaps even on
other icy planets in the solar system such as below the
Martian ice caps or in the ice-covered oceans of Europa,
a moon of Jupiter.
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National
Science Foundation -
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