Gone South for the Winter
Geologist Brenda Hall combs Antarctica's icy shorelines and polar
deserts for evidence of prehistoric climate change
About the Photo:
Brenda Hall started her Antarctica research as a graduate student,
mapping the moraines adjacent to the glaciers. More than a decade
later, she continues to work in this area.
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Sometimes, when Brenda Hall has just
returned from four months on a research expedition in Antarctica, she
sits in her small office at the University of Maine, looks out the
window, and wonders if she's dreaming.
"You're in a bit of a daze when you first come back," says the
34-year-old geologist. "You wake up, expecting to be in your tent. You
listen for the constant wind, and it's not there. You smell the plants,
you see colors again. You notice it getting dark, after months of
round-the-clock daylight."
Hall, a research assistant professor in the Climate Change Institute and
Department of Earth Sciences, is at home in both worlds. She lives a
busy academic life in Orono and beyond: teaching, writing journal
articles, speaking at scholarly meetings, peering into microscopes at
fossil algae and bits of ancient sealskin, examining sediment cores and
conducting radioactive dating tests.
And then there's her adventurous, dangerous, exhilarating life on
fieldtrips to Earth's southernmost continent during the Antarctic summer
— November–February — when she camps at the edge of the vast East
Antarctic Ice Sheet and in a "frozen desert" region of the
Transantarctic Mountains known as the Dry Valleys.
"Going to Antarctica is probably the most daring thing anyone in my
family has ever done," Hall says with a laugh. "It's much better than
Maine in January. I just tell everyone I go south for the winter."
But Hall is no tourist. She's a respected member of the small community
of glacial geologists, oceanographers and climatologists that studies
the Antarctic, including seasoned colleagues such as UMaine's George
Denton and Wallace Broecker of Columbia University's Lamont-Doherty
Earth Observatory.
Her mission is to find clues, often subtle and deeply hidden, to global
climate changes that have triggered ice ages in the past. By studying
the melting history of the West Antarctic Ice Sheet and uncovering
evidence for huge lakes in the Dry Valleys that grew and shrank with
surprising rapidity, Hall is making key discoveries about the complex,
interrelated mechanisms that drive worldwide climate.
"Antarctica has the potential for discovery. It offers the opportunity
to find significant things that no one else has ever found," she says.
"There aren't many places where someone can do that anymore."
Hall, the oldest of two daughters of primary school educators, grew up
in Standish, Maine. Her now retired parents raise wild blueberries in
western Maine, and she spends the first two weeks of August raking
berries in the family's fields.
"It's taught me hard work," she says. "And that's been good for doing
research in Antarctica, spending months at a time on your hands and
knees looking for algae the size of cornflakes."
After earning her bachelor's degree in geology and Russian from Bates
College — she speaks Russian, Finnish, Spanish, and "a little" Italian
and German — Hall went on for her master's and Ph.D. in geological
sciences at UMaine, where Denton was her thesis advisor.
"Brenda is very dogged in her approach, very dedicated," says Denton, a
veteran of 30 Antarctic expeditions who led a fieldtrip in 1990 that was
Hall's first visit to the icy continent. "She's bitten by a real love of
science, something that not all scientists have."
Hall's lasting impressions of that first trip and subsequent visits
include the challenge of just getting to the huge, remote continent
that, at 14 million square miles, is the size of the United States and
Mexico combined. To reach the Dry Valleys, the researchers travel to
Christchurch, New Zealand, and fly by military aircraft to McMurdo
Station, headquarters for U.S. polar programs sponsored by the National
Science Foundation (NSF). Helicopters then ferry them to field sites
hundreds of miles away. McMurdo also is the departure point for trips to
the West Antarctic Ice Sheet.
Some of Hall's fieldwork has been conducted on the South Shetland
Islands, just off the tip of the Antarctic Peninsula. To reach that
site, scientists fly to Punta Arenas, Chile, and then brave the Drake
Passage on a sometimes wild four-day boat ride.
"These are the worst seas in the world," she says. "Last year, a cruise
ship that followed right after us took a 50-degree roll."
Her West Antarctic Ice Sheet investigations, ongoing since graduate
school, were prompted by concerns that the massive structure could
collapse and raise worldwide sea levels by up to 18 feet. "There's some
evidence it has totally disintegrated before," says Hall. The ice sheet,
unlike others in Antarctica, is inherently unstable because it rests on
bedrock and marine sediments as much as 8,000 feet below the ocean
surface, and is thought to be closely tied to sea level changes.
To help predict the future, Hall looks at the past. She and her team use
tweezers and dinner spoons to collect tiny bits of algae, mollusk shells
and sealskin deposited in "raised beaches" that progressively mark the
ice sheet's retreat from the last glacial maximum 18,000 years ago.
Radioactive dating of that preserved organic material reveals that the
ice began rapidly shrinking about 8,000 years ago.
The surprise in her research is that the melting lagged millennia behind
the advent of sea level rise 17,000 years ago as the last ice age ran
out of steam, and may be continuing today even though sea level largely
stabilized 7,000 years ago. "It's clear there's more at work here than
just sea level rise, maybe some internal mechanism in the ice that is
still operating today," says the UMaine scientist, who adds there is
insufficient data so far to determine if the melting occurred smoothly
or in fits and starts. "We're trying to isolate that mechanism."
Hall has found other clues to the ice age puzzle in a region that belies
the popular image of Antarctica: the Dry Valleys, a mountainous polar
desert area bordering the Ross Sea, with average annual temperature of
-22 degrees F and less than 0.4 inches of precipitation a year. Supplied
by helicopter flights from McMurdo Station, her field site on the
barren, ice-free landscape — "like going to another planet" —consisted
last year of nine people camped in sturdy canvas "Scott" tents that
resist the relentless wind.
"It's always blowing, but the worst are the katabatic windstorms that
come in off the ice sheet at 100 miles an hour. There's constantly
one-inch gravel flying through the air, you can hear it roaring, you can
see these dust devils coming down the valley on the wind in October,"
says Hall. "There's always danger in the Antarctic. You have to know
your limits and be prepared."
After more than a dozen visits, she is still inspired by the exotic
beauty of Antarctica, the "wonderful" 24-hour sun, the immense scale of
earth and sky, even the sharp-toothed fur seals that chase her on
occasion.
"Sometimes, you come across places that are just so absolutely
beautiful, you can't describe them," she says. "When you're there,
you're so apart from the rest of the world, it's like nothing else
exists."
It was in the Dry Valleys that Hall uncovered evidence for several
mammoth freshwater lakes that once bordered the West Antarctic Ice Sheet
when it filled the Ross Sea during the last glaciation. At their maximum
extent, ice-covered Glacial Lake Wright and Glacial Lake Victoria were
up to 1,600 feet deep and flooded nearly 40 square miles in their
respective valleys. By radiocarbon dating algae from the former
shorelines, she found the lakes existed from 25,000 years ago until at
least 8,000 years ago, and fluctuated in water level by hundreds of feet
every 700–1,500 years. Only a remnant of Victoria still exists: Lake
Vida, 40 feet deep and more than 2 miles square.
"There had to be very dramatic shifts in local climate to cause these
meltwater fluctuations," Hall says. "No one knows what causes such
abrupt climate change. If it correlates with global fluctuations, then
we look to the atmosphere. If there's no global synchrony, then changes
in deep-ocean circulation could be the forcing mechanism. Or it could be
a combination." Understanding rapid climate change is critical, because
many scientists now believe that the major global cooling that precedes
ice ages can occur in decades or less.
Her fieldwork is helping to test the so-called "Bipolar SeeSaw" theory,
championed by Lamont-Doherty's Broecker, that circulation patterns of
two great ocean systems — the North Atlantic Deepwater and the Antarctic
Bottom Water — affect global climate. According to the theory, when one
system strengthens, the other weakens, which means the climate of
Antarctica is out-of-phase and may exhibit telltale changes long before
the rest of the globe.
What about human-caused global warming? "I don't believe we should be
putting all these things into the atmosphere," says Hall. "But when you
deal with climate on millennial scales, you gain an appreciation for how
complicated it is and how little we really know. Perhaps you need
thousands of years of record before you can identify meaningful trends."
Hall's busy schedule has her back in Antarctica this season on a
three-year NSF grant to core the Dry Valleys' lakes and on several
additional projects, and she feels a bit conflicted about leaving home
for such long periods of time. Her husband, Bret Overturf, an
archaeologist who accompanied Hall on three fieldtrips, now stays behind
at their 80-acre farm in Corinth with the couple's three young children.
"My goal is one and a half months in the field instead of four months,"
she says firmly, then pauses and looks out her office window. "But you
know, around mid-October, I start getting itchy feet."
by Luther Young
November-December, 2003
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