News: New life beneath sea and ice

New life beneath sea and ice

Scientists have long known that life can exist in some very extreme
environments. But Earth continues to surprise us. At a European Science
Foundation and COST (European Cooperation in the field of Scientific and
Technical Research) 'Frontiers of Science' meeting in Sicily in October,
scientists described apparently productive ecosystems in two places where
life was not known before, under the Antarctic ice ***, and above
concentrated salt lakes beneath the Mediterranean.

In both cases, innumerable tiny microbes are fixing or holding onto
quantities of organic carbon large enough to be significant in the global
carbon cycle.

Lakes under the ice

Brent Christner of Louisiana State University, in the US, told the
conference about the microbes living within and beneath the ice on
Antarctica. In the last decade, scientists have discovered lakes of liquid
water underneath the Antarctic ice ***. So far we know of about 150 lakes,
but this number will probably increase when the entire continent has been
surveyed. These lakes occur as a result of geothermal heat trapped by the
thick ice, melting it from underneath, and the great pressure from the ice
above, which lowers the melting point of water.

The largest subglacial lake, Lake Vostok, lies beneath the coldest place on
the planet, where the temperature at the surface often falls below 60 C.
"It's the sixth largest freshwater lake on the planet by volume, and about
the size of Lake Ontario," says Christner. "If you were on a boat in the
middle of the lake, you would not see shores."

Christner has examined microbial life in ice cores from Vostok and many
other global locations. While direct samples of water from subglacial
Antarctic lakes have yet to be obtained, the lower 80m or so of the Vostok
ice core represents lake water that progressively freezes onto the base as
the ice *** slowly traverses the lake. "Microbial cell and organic carbon
concentrations in this accreted ice are significantly higher than those in
the overlying ice, which implies that the subglacial environment is the
source," says Christner.

Based on accumulating measurements of microbes in the subglacial
environment, he calculates that the concentration of cell and organic carbon
in the Earth's ice sheets, or 'cryosphere', may be hundreds of times higher
than what is found in all the planet's freshwater systems. "Glacial ice is
not currently considered as a reservoir for organic carbon and biology,"
says Christner, "but that view has to change."

Salt below the sea

Beneath the Mediterranean lurks a similar surprise. Michail Yakimov of the
Institute of the Coastal Marine Environment, Messina, Italy is a project
leader for the European Science Foundation's EuroDEEP programme on ecosystem
functions and biodiversity in the deep sea. His team studies lakes of
concentrated salt solution, known as anoxic hypersaline basins, on the floor
of the Mediterranean. They have discovered extremely diverse microbial
communities on the surfaces of such lakes.

The anoxic basins, so called because they are devoid of oxygen, occur below
3,000 m beneath the surface and are five to ten times more saline than
seawater. One theory says they exist uniquely in the Mediterranean, because
this sea entirely evaporated after it was cut off from the Atlantic around
250 million years ago. Its salt became a layer of rock salt, called
evaporite, which was then buried by windblown sediment. Now the sea is
filled again, the salt layer has been exposed in some places, perhaps by
small seaquakes, and the salts from the ancient Mediterranean have dissolved
again, making the water very salty.

Despite the harsh conditions, hypersaline brines have been shown to possess
a wide range of active microbial communities. Together with other
international partners, Yakimov's team has already identified more than ten
new lineages of bacteria and archaea (these are ancient bacteria-like
organisms), which they have named the Mediterranean Sea Brine Lake
Divisions.

There is ample life at the boundary between the concentrated basin and the
ordinary seawater. "Because of the very high density of the brine, it does
not mix with seawater," he explains, "and there is a sharp interface, about
1m thick."

In that layer, microbial diversity is incredibly rich. The research shows
that these microbes largely live by sulphide oxidation. Like the communities
at hydrothermal vents in the deep ocean, they can survive independently of
sunlight and oxygen. But they are an important store for organic carbon.
"The deep-sea microbial communities in the Mediterranean fix as much or even
more carbon dioxide each year as those in the surface layers," says Yakimov.
"This carbon sink should be taken into account at the global scale."

Source: European Science Foundation
http://www.physorg.com/news146140920.html

Posted by
Robert Karl Stonjek


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