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Study Finds Ancient Warming Greened
Antarctica

06.17.12

This artist's rendition created from a photograph of
Antarctica shows what Antarctica possibly looked like during the middle Miocene
epoch, based on pollen fossil data. Image credit: NASA/JPL-Caltech/Dr. Philip
Bart, LSU
›
Full image and caption

Pollen grains and leaf waxes record vegetation on
Antarctica during a time of global warmth 20-15 million years ago, when
greenhouse gas concentrations may have been similar to projections for the end
of the 21st Century. Image credit: Sophie Warny and Kate Griener (Louisiana
State University, Baton Rouge)
› Full image
and caption

Rendering of drilling operations during the ANDRILL
campaign in Southern McMurdo Sound, Antarctica, October – December 2007. Image
credit: University of Nebraska-Lincoln
› Full image and
caption

Palynologist and study co-author Sophie Warny
(Louisiana State University) and Ian Raine (GNS, New Zealand), examine some of
the ANDRILL sediment core samples used in the Nature Geoscience Antarctica
study. Image credit: Louisiana State University
› Full
image and caption

PASADENA, Calif. -- 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 continent.

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.

This research was funded by the U.S. National Science Foundation with
additional support from NASA. The California Institute of Technology in Pasadena
manages JPL for NASA.

For more information about NASA programs and projects, visit: http://www.nasa.gov/ .

Alan Buis 818-354-0474
Jet
Propulsion Laboratory, Pasadena, Calif.
[email-masked]

J. D.
Harrington 202-358-5241
NASA Headquarters, Washington

[email-masked]

Robert Perkins 213-740-9226
University of
Southern California, Los Angeles
[email-masked]

Zac Lemoine
225-578-1399
Louisiana State University, Baton Rouge
[email-masked]

2012-179

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