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November / December 2003

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Gone South for the Winter

Photo courtesy of Brenda Hall

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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