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From Staff Reports
Antarctica once enjoyed summer-time temperatures that
averaged 10 degrees Celsius — a climate more suited
for a warm fleece than a thick parka — about 15.7
million years ago.
That’s the conclusion scientists drew from the discovery
of a thick layer of fossils from marine algae and the
pollen of woody plants in a sediment core drilled into
the seafloor of McMurdo Sound in 2007.
Researchers with the ANtarctic Geological DRILLing Program
(ANDRILL) published their research this month in the issue
of Geology, the journal of the Geological Society of America.
Sophie Warny , an assistant professor of geology and
geophysics at Louisiana State University , found the first
indication of the warm period while studying samples from
the project last year. One sample, she said in a press
release, stood out as a complete anomaly.
“First I thought it was a mistake, that it was a
sample from another location, not Antarctica, because
of the unusual abundance in microscopic fossil cysts of
marine algae called dinoflagellates. But it turned out
not to be a mistake, it was just an amazingly rich layer,”
Warny said.
ANDRILL took two sediment cores near the U.S. Antarctic
Program’s McMurdo Station over two successive field
seasons beginning in 2006. The $30 million ANDRILL program
was one of the premiere projects of the International
Polar Year , a two-year scientific campaign that officially
ended in March 2009. The National Science Foundation (NSF)
funded about two-third of the program, with international
partners New Zealand, Italy and Germany funding the remainder.
The microscopic fossils were found in unusual abundance
in a two-meter-thick layer from the 2007 core of seafloor
sediments that measured more than 1,100 meters long.
“We all analyzed the new samples and saw a 2,000-fold
increase in two species of fossil dinoflagellate cysts,
a five-fold increase in freshwater algae and up to an
80-fold increase in terrestrial pollen,” Warny said.
“Together, these shifts in the microfossil assemblages
represent a relatively short period of time during which
Antarctica became abruptly much warmer.”
This apparent bloom of life in Antarctica occurred during
a generally warm time referred to as the Mid-Miocene Climatic
Optimum, according to the scientists. This was a time
when global temperatures were warmer than at present.
It could serve as an analogue to how the ice sheets of
today may respond to warming temperatures in the coming
century.
“This event will lead to a better understanding
of global connections and climate forcing,” said
David Harwood , professor of geosciences at the University
of Nebraska-Lincoln and research director for ANDRILL’s
Science Management Office. “In other words, it will
provide a better understanding of how external factors
imposed fluctuations in Earth’s climate system.”
ANDRILL scientists say these findings corroborate and
expand evidence for lakes and vegetation farther inland
in the nearby McMurdo Dry Valleys . In that separate study,
also funded by the NSF, scientists discovered the last
traces of tundra in the form of fossilized plants and
insects.
That research team — headed by David Marchant ,
an earth scientist at Boston University , and Allan Ashworth
and Adam Lewis , geoscientists at North Dakota State University
— concluded from fossilized evidence that the climate
cooled abruptly about 14 million years ago. Their findings
appeared in the Aug. 4, 2008 edition of the Proceedings
of the National Academy of Sciences.
Earlier this year, ANDRILL scientists published two papers
in the journal Nature, including one that suggested even
a slight rise in atmospheric concentrations of carbon
dioxide, one of the gases that drives global warming,
affects the stability of the West Antarctic Ice Sheet
(WAIS). The ice sheet contains enough ice to raise sea
level by about six meters.
The evidence from the 2006 core, nearly 1,300 meters
long, traveled back in time to the Pliocene era, roughly
2 million to 5 million years ago. During that era, Antarctica
was also warmer than today, and atmospheric carbon dioxide
levels were higher. Data from the core indicate the ice
sheet advanced and retreated numerous times in response
to climate changes.
“Geological archives, such as the ANDRILL core,
highlight the risk that a significant body of permanent
Antarctic ice could be lost within the next century as
Earth’s climate continues to warm,” said Tim
Naish , director of Victoria University of Wellington's
Antarctic Research Centre and co-chief scientist during
the first ANDRILL field season.
“Based on ANDRILL data combined with computer models
of ice sheet behavior, collapse of the entire WAIS is
likely to occur on the order of 1,000 years, but recent
studies show that melting has already begun,” said
Naish when Nature published the papers in March 2009.
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