Tuesday, June 19, 2012

The tale of continents: How greener was my Antarctica of the yore!

Large quantities of pollen and algae in sediment cores were taken around
Antarctica. Fossils of plant life in Antarctica are difficult to come by because

the movement of the massive ice sheets covering the landmass grinds and scrapes
away the evidence

A new university-led study with NASA participation finds
ancient Antarctica was much warmer and wetter than previously
suspected. The climate was suitable to support substantial vegetation
-- including stunted trees -- along the edges of the frozen

The team of scientists involved in the study, published online June 17
in Nature Geoscience, was led by Sarah J. Feakins of the University
of Southern California in Los Angeles, and included researchers from
NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Louisiana
State University in Baton Rouge.

By examining plant leaf wax remnants in sediment core samples taken
from beneath the Ross Ice Shelf, the research team found summer
temperatures along the Antarctic coast 15 to 20 million years ago
were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today,
with temperatures reaching as high as 45 degrees Fahrenheit (7
degrees Celsius). Precipitation levels also were found to be several
times higher than today.

"The ultimate goal of the study was to better understand what the
future of climate change may look like," said Feakins, an assistant
professor of Earth sciences at the USC Dornsife College of Letters,
Arts and Sciences. "Just as history has a lot to teach us about the
future, so does past climate. This record shows us how much warmer
and wetter it can get around the Antarctic ice sheet as the climate
system heats up. This is some of the first evidence of just how much
warmer it was."

Scientists began to suspect that high-latitude temperatures during the
middle Miocene epoch were warmer than previously believed when
co-author Sophie Warny, assistant professor at LSU, discovered large
quantities of pollen and algae in sediment cores taken around
Antarctica. Fossils of plant life in Antarctica are difficult to come
by because the movement of the massive ice sheets covering the
landmass grinds and scrapes away the evidence.

"Marine sediment cores are ideal to look for clues of past vegetation,
as the fossils deposited are protected from ice sheet advances, but
these are technically very difficult to acquire in the Antarctic and
require international collaboration," said Warny.

Tipped off by the tiny pollen samples, Feakins opted to look at the
remnants of leaf wax taken from sediment cores for clues. Leaf wax
acts as a record of climate change by documenting the hydrogen
isotope ratios of the water the plant took up while it was alive.

"Ice cores can only go back about one million years," Feakins said.
"Sediment cores allow us to go into 'deep time.'"

Based upon a model originally developed to analyze hydrogen isotope
ratios in atmospheric water vapor data from NASA's Aura spacecraft,
co-author and JPL scientist Jung-Eun Lee created experiments to find
out just how much warmer and wetter climate may have been.

"When the planet heats up, the biggest changes are seen toward the
poles," Lee said. "The southward movement of rain bands associated
with a warmer climate in the high-latitude southern hemisphere made
the margins of Antarctica less like a polar desert, and more like
present-day Iceland."

The peak of this Antarctic greening occurred during the middle Miocene
period, between 16.4 and 15.7 million years ago. This was well after
the age of the dinosaurs, which became extinct 64 million years ago.
During the Miocene epoch, mostly modern-looking animals roamed Earth,
such as three-toed horses, deer, camel and various species of apes.
Modern humans did not appear until 200,000 years ago.

Warm conditions during the middle Miocene are thought to be associated
with carbon dioxide levels of around 400 to 600 parts per million
(ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the
highest they've been in the past several million years. At the
current rate of increase, atmospheric carbon dioxide levels are on
track to reach middle Miocene levels by the end of this century.

High carbon dioxide levels during the middle Miocene epoch have been
documented in other studies through multiple lines of evidence,
including the number of microscopic pores on the surface of plant
leaves and geochemical evidence from soils and marine organisms.
While none of these 'proxies' is as reliable as the bubbles of gas
trapped in ice cores, they are the best evidence available this far
back in time. While scientists do not yet know precisely why carbon
dioxide was at these levels during the middle Miocene, high carbon
dioxide, together with the global warmth documented from many parts
of the world and now also from the Antarctic region, appear to
coincide during this period in Earth's history.

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