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By
Peter Rejcek
Antarctic science requires many different methods in the
pursuit of knowledge about the seventh continent and its
place in the global ecosystem. The deeply browned face
and ruddy cheeks of Paul Mayewski tell a story of scientists
who understand the value of spending extended time in
the environment they study.
“That’s very important,” said Mayewski,
the director of the Climate Change Institute at the University
of Maine. “It allows the scientists to develop, not
just a scientific explanation, but an intuition about
what the environment is like. That’s what we do:
we’re interpreting the environment. If you don’t
live in it, spend a lot of time in it, it’s very
hard to do.”
Mayewski and colleagues from three other institutions
completed a month-long overland traverse of a short stretch
of East Antarctica in mid-January as part of the United
States component of the International Trans Antarctic
Scientific Expedition (ITASE). Twenty nations comprise
ITASE, a cooperative effort to describe and understand
Antarctic environmental change in a regional and global
context over the last 200 to 1,000 years.
They can reconstruct the climate and atmospheric conditions
by collecting samples and data through a variety of methods
such as drilling ice cores to 100 meters, using ground-penetrating
radar that peers to the bedrock underneath the ice sheets,
and mapping the topography of the surface with high-precision
GPS.
The program’s overarching goal is to develop a baseline
of data about Antarctica’s climate to help interpret
whether future changes around the continent are part of
a natural pattern or anomalies caused by human influences
as the global climate changes, according to Mayewski.
“Our goal, along with all the other ITASE countries,
is to put together a reconstruction for climate in at
least the last 200 years,” he explained, “…
if not back to a thousand years, and use that to understand
how the system operates and to determine whether the changes
that are occurring now are unique.”
The timelines are not arbitrary. The 200-year timeframe
encompasses a period when the human fingerprint from pollutants
should begin to show itself in the chemistry of the ice
cores. The relatively brief time period also lends itself
to easier dating of the layers of the ice cores, which
scientists read like tree rings. For example, researchers
can identify sulfate concentrations from the major eruption
of Indonesia’s Mount Tambora in 1815.
“This means we can calibrate our records back to
that,” Mayewski said.
And in the last millennium, there have been documented
natural climatic cycles of warmer and colder periods.
The scientists want to characterize these natural variations
to determine if future climate anomalies are analogous
to the past or not.
Down to a quadrillion
The Antarctic continent is far from being one huge, homogenous
ice cube. ITASE scientists have found from their first
series of traverses from 1999 to 2003 across West Antarctica
great variability in snow accumulation rates as well as
some of the reasons behind that variance. They determined
precipitation in the interior of the continent is relatively
stable but also identified some regions of the Antarctic
that may be on the verge of dramatic change.
“It’s an immense place, and there’s a lot
of variability. It’s so dynamic it may not be that
easy to tell how much it’s going to change,”
said Mayewski, the principal investigator of the 13-person
team that traveled on sleds and farm tractors – two
Caterpillar Challenger 55s – across 460 kilometers
of snow and ice.
“This place is potentially a bellwether for what’s
happening in the whole planet,” he added.
The group started the scientific traverse on Dec. 13 from
Taylor Dome, an elliptical ice ridge that rises about
2,400 meters above sea level. Its equipment had been left
at Taylor Dome following a logistics traverse from the
South Pole during the 2003-04 austral summer season.
Dan Dixon, an ITASE veteran, also participated in the
South Pole to Taylor Dome journey, collecting ice cores
from East Antarctica along the 2,500-kilometer route.
A doctoral student from the Climate Change Institute,
Dixon researches past Antarctic climate using ice core
chemistry.
Lab analysis of the cores has revealed the start of anthropogenically
introduced chemicals such as lead, although increased
levels of pollutants such as nitrate and sulfate, which
are very high in the Northern Hemisphere, are not yet
rising over Antarctica. Advances in lab analysis allow
Dixon and others to make chemical measurements of the
atmosphere in the ice cores down to one part per quadrillion.
“We’re almost down to atoms,” Dixon said.
Down to the bedrock
The team also uses several different types of radars for
its work on the ice sheet. One is ground-penetrating radar
that looks at the upper 15 meters of ice. It is used primarily
for operations – snooping out crevasses. The radar
is attached to a 10-meter-long boom in front of a PistenBully
that rides at the head of the heavy traverse train.
“This is a critical piece of safety equipment for
the team as crevasses, cracks in the ice, can be so large
here that the trains could literally be swallowed up,”
wrote Lora Koenig on the team’s online journal while
it was at Taylor Dome preparing for the traverse. Koenig,
a doctoral student at the University of Washington, is
interested in how space-borne satellites monitor snow
properties over ice sheets. During the traverse, she also
used high-frequency radar to penetrate the top meter of
snow to image grain size, stratigraphy and thermal conductivity.
She will compare those measurements to models of microwave
remote sensing data of the ice sheet to determine the
accuracy of the latter.
Another radar penetrates about 100 meters, the same depth
of the deepest cores the team took this season. Finally,
deep-penetrating radar can see down thousands of meters
to the sub-glacial bedrock. The radar operated continuously
and picked out details of the bedrock the scientists had
not seen before, as well as the existence of a couple
of small, sub-glacial lakes.
“We’re interested in understanding, from this
radar, the ice dynamics,” Mayewski said. Based on
data from previous ice cores, the team can use the radars
to find certain reflectors in the ice that it can date
to a certain time period. The scientists then calculate
the changes in snow accumulation while dragging the radar
along the traverse route.
Brian Welch from St. Olaf College in Minnesota operated
the deep radar system, which trailed behind on a separate
sled at the end of one of the two tractor trains. The
instrument can detect whether water sits between the top
of the bedrock and the bottom of the ice sheet. That’s
important for understanding ice flow: the ice moves faster
if it’s not frozen to the bedrock.
“At Byrd Glacier, the bedrock is really, really bright,”
said Welch, who accompanied the ITASE team on three previous
traverses of West Antarctica. “That means there’s
water down there. If there’s water there, the ice
can start flowing much faster.
“[East Antarctica] looks a lot more like what you
would expect if you were doing seismology in sand dune
areas than what you would expect to see in East Antarctica,”
he added. “East Antarctica is a much more dynamic
place than we thought it was.”
Down to the core
Gordon Hamilton is another ITASE member with previous
Antarctic field experience in the program. A research
associate professor at the Climate Change Institute, Hamilton
studies the topography of the ice sheet to understand
how it affects the speed of the wind across the surface,
a factor in the transportation and accumulation of snow.
He also uses high-precision GPS to create a detailed map
of the sampling areas.
“For understanding the ice core record, we have to
know what the surface slope is from where the cores are
[taken],” Hamilton explained.
In a related ITASE project, Hamilton revisited previous
traverse sampling sites near the WAIS Divide field camp
in West Antarctica with graduate student Leigh Stearns.
The surveys will help the researchers calculate ice flow
velocities and determine rates of ice sheet thickness
change.
Another one of Hamilton’s research goals is to understand
the contribution of ice sheet melt to sea level rise.
Satellite imagery can determine thickness but not density,
hence the need for the ice cores.
His graduate student, physicist Dan Breton, built an ice
core density analyzer that the team uses to image the
ice cores during the traverse.
The density gauge uses low-energy gamma rays to determine
the ice density, not unlike a bone density scan that uses
X-rays to determine density by the absorption of the beam.
Each density test on a one-meter-long sample can take
upwards of 45 minutes to complete.
The first-year Ph.D. student said he had a relatively
short time to assemble the instrument and looks forward
to making some tweaks before next year’s field season,
which is scheduled to end at South Pole.
“It’s really been a scramble to design it, engineer
it, fix everything that didn’t work and get it ready
to go,” he said of the homemade density analyzer.
This was Breton’s first season in Antarctica. Expecting
temperatures on the polar plateau in at least the negative
40 degrees Celsius range, he built a large, insulated
wood box to hold all of the electronics for the density
analyzer. It turned out the austral summer was not so
harsh, and Breton’s equipment overheated. He had
to drill holes in the box to provide ventilation.
“Until you have a firsthand knowledge of what it’s
really like [here],” he noted, “it’s difficult
to design instrumentation that’s really fit for what
you’re doing.”
Down for next season
Andrei Kubatov said that ITASE is not only a unique platform
for science but an excellent opportunity for teaching
young scientists in the field.
“It’s very important,” said Kutabov, a
research assistant professor with the Climate Change Institute
whose work revolves around how volcanic eruptions force
climate change.
Mayewski likened the experience to an apprenticeship.
“We like to think we’re producing field savvy
scientists who can take care of themselves really well
in these extreme environments and understand how to have
a good time and do a lot of good science,” he said.
For Koenig, the University of Washington graduate student,
the traverse got her out from behind a computer screen
and into an environment where “every day was different.”
“I usually look at ice sheets from a satellite,”
she said.
Next year, the ITASE team will have to cover far more
ground to reach the South Pole from where it left its
equipment and vehicles. Several other countries are also
doing ITASE traverses next year in conjunction with the
International Polar Year, according to Mayewski.
“There’s plenty more to learn in East Antarctica,”
Mayewski said. “Every year the program gets better
and better.”
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