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Global Warming: the Archaeological Frontier

Melting glaciers yield evidence on new theories of Asian migration to the Americas. Underwater robots search the sea bottom, looking for more.

In the small laboratory next to his office at the Maxwell Museum of Anthropology in Albuquerque, N.M., Jim Dixon unlocks a large steel cabinet, slides open a drawer and gingerly lifts out a thin piece of gray, brittle-looking wood. "This fragment is actually a spear shaft," he says and then shows me a dart shaped to fit into the socket of an ancient spear-thrower called an atlatl. "This is the stone point with sinew lashing. This is very fragile. This is about 2,800 years old."

Opening one drawer after another, Dixon displays dozens of other artifacts — arrows, some decorated with red ochre, the fletching still attached, and arrowheads carved from stone and caribou antler. There is even a rare arrow point hammered from a nugget of copper.

Dixon has discovered these ancient hunting implements over the past decade in the unlikeliest of places — patches of melting ice high in the mountains of southeastern Alaska. Set in sheltered basins and seldom more than a few acres in size, these durable accumulations of snow and ice have built up over thousands of years, remaining intact throughout the short sub-Arctic summers. "They've been uniquely preserved in these frozen environments," Dixon says of his collection of fragile organic artifacts. "They give us a glimpse of the archaeological record that we don't ordinarily get."

During a few weeks each August — the brief window for high-latitude fieldwork — Dixon and his team fly around Wrangell-St. Elias National Park and Preserve in a helicopter, setting down at remote ice patches to conduct ground searches along their melting edges. The artifacts are often lying in the open, waiting to be picked up, like shells on a beach at low tide.

More of these objects are coming to light as warming temperatures shrink the ice patches where they have been preserved. This invests the ongoing search with promise and urgency, he says.

"This is a phenomenon that's going on globally," Dixon says. "Ancient ice is melting for the first time. We know that because the types of artifacts that are coming out are organic — they're very fragile, and they decompose very rapidly, within just a matter of years when they've been exposed from the ice. So we know they haven't been laying on the surface there for thousands of years."

Large-diameter dart shafts recovered from Yukon. Each black or white rectangle in the pictured scaling bars is 1 centimeter long. (Government of Yukon)

Large-diameter dart shafts recovered from Yukon. Each black or white rectangle in the pictured scaling bars is 1 centimeter long. (Government of Yukon)

As a leading expert on the early settlement of western North America, Dixon has made a career out of challenging academic orthodoxy and looking for fresh archaeological evidence in unexpected places. Lately, he has been exploring the shallow waters off the Alaska Panhandle with a remotely operated underwater vehicle, trying to prove a theory that people first migrated to North America during the last ice age by following the north Pacific coast, rather than hiking the inland route that most scientists favor.

"He's not hung up on safe science and reproducing the same results that someone else has done," says Craig Lee, a colleague who had Dixon as his doctoral adviser. "He definitely would be in the vanguard of discovery when it comes to finding stuff. This ice patch research — that's going out on a limb."

"I always had a curiosity as a child about the past," Dixon says, sheepishly admitting to picking up arrowheads in the cornfields near his New Jersey home — something professionals frown upon as akin to pot hunting. Later, while earning a master's degree in anthropology at the University of Alaska Fairbanks, Dixon joined in an archaeological survey along the planned route of the Trans-Alaska Pipeline and discovered a number of early Native-American sites, including one that was more than 10,000 years old.

Dixon later taught and served as curator of archaeology at the UAF museum. He became curator of archaeology at the Denver Museum of Natural History in 1994, then was hired by the University of Colorado to head its graduate program in museum studies and serve as a research fellow at the Institute of Arctic and Alpine Research. The University of New Mexico lured him away to head the Maxwell Museum in December 2007.

Dixon has long been interested in how the first humans arrived in the New World. The dominant theory is that hunters from Siberia crossed the Bering land bridge that emerged during the last ice age some 13,000 years ago, when sea levels were lower. They are thought to have moved into North America through an ice-free corridor between the Cordilleran and Laurentide ice sheets that covered much of the continent at the time, evolving into the so-called Clovis culture that was widespread throughout North America.

But there is a growing body of contradictory evidence.

"I think several of us had been struggling for years with this idea that there were a number of archaeological sites throughout the Americas that appeared to predate the Clovis culture. The most parsimonious explanation was some kind of a coastal route," says Dixon, who spelled all this out in his 1999 book Bones, Boats and Bison: Archaeology and the First Colonization of Western North America. "Along the north Pacific Rim seemed to be the most plausible because of the great genetic similarity between Native-American populations and the people of northeast Asia."

During the last ice age, warm Pacific waters kept the northwest coast free of glacial ice, he says, and dry land extended well out onto the continental shelf. Paleontologists have found the remains of large mammals like the brown bear and caribou, as well as seals, fish and waterfowl — all of which could have sustained ancient hunters.

"If you know how to hunt and fish those animals, you're basically adapted to this entire environment," Dixon says, "and whether you're in Oregon or Hokkaido, it basically doesn't matter, in terms of making a living." All he needs now, he adds with a wry laugh, is the archaeological evidence to prove his theory.

Enter the underwater robot. Dixon has had graduate student Kelly Monteleone putting data for the continental shelf around southeast Alaska's Alexander Archipelago into a geographic information system database. The mapping system helps pinpoint search locations for Dixon's team members, who guide the remotely operated vehicle from the deck of their research vessel — a converted fishing trawler. The robot scans the ocean bottom for signs of ancient human habitation, such as shell middens, charcoal, stone chips and pit house foundations.

"It's just a vast frontier," Dixon says. "To try to pinpoint specific spots is the trick, and that's what we're trying to do now."

Epic archaeological finds often involve a bit of luck, as Greg Hare can attest. In 1997, a Canadian wildlife biologist hunting in the mountains of the southern Yukon Territory discovered a huge field of melting caribou dung in a mountainside ice patch. On a return visit with another biologist, he found a small stick with what looked like a string attached. They brought the object to Hare, a government archaeologist based in Whitehorse, Yukon. "We looked at it and thought, 'Wow, it looks like part of an arrow,'" Hare remembers.

He had the stick radiocarbon dated: It was 4,300 years old. Dung samples collected from a core drilled through the ice patch were more than 2,000 years old. Hare, whose job usually consisted of conducting archaeological surveys in advance of construction projects, knew he was on to something.

The next year, he and a team found artifacts at several sites, including an arrow shaft that was 6,800 years old. Since then, Hare has explored scores of dung-tinted ice patches, two dozen of which have archeological deposits.

Why were the artifacts so closely associated with evidence of caribou? Hare thinks it has to do with the creatures' migratory habits. Superbly adapted to arctic winters, they need to cool off and escape bugs in the summer heat, so they congregate on ice patches.

"That's a pattern that obviously gave a real advantage to hunters, because they knew where they had a good likelihood of running across groups of caribou," Hare observes.

Building on Hare's findings, Dixon decided to search in nearby Wrangell-St. Elias National Park, home to 18,000-foot Mt. St. Elias, the second-highest peak in the U.S., and hundreds of glaciers and ice patches. But his application to the National Science Foundation for research funding was met with skepticism. "Some of the reviews said things like, 'This is the most absurd thing we've ever heard of, because we know people didn't live on ice,'" Dixon recalls. "They really didn't get the complexity of it."

Along with Hare, Dixon is a "foundational figure" in gaining scientific acceptance for the validity of ice patch research, says Craig Lee, who has collaborated with Dixon in some of his fieldwork and conducted his own research in the Rocky Mountains and Alaska's Denali National Park and Preserve. "It was Jim who said, 'Hey, there's a chance that this is not a localized phenomenon. It's not restricted to this little area, and there may be material that may be showing up in other spots.'"

In Wrangell-St. Elias, Dixon found artifacts in five of some 200 ice patches he surveyed. The search process is decidedly unglamorous. It starts with the pungent odor of thousand-year-old decomposing caribou dung. ("One of the tricks for searching for these is, 'Look for the brown ice,'" he confides). Far above timberline, Dixon and his team (some of whom are Native Americans) scout for pieces of wood, knowing only humans could have brought them. Often, the objects are half-buried in melting slush.

Dixon's artifact collection includes two rare darts from atlatls — the lever-like spear-throwers that enabled Native-American hunters to bring down large game. Some of the arrows feature "ownership marks" carved by their makers. They're exactingly crafted from white spruce and fletched with feathers from birds of prey.

Each arrow represents a major investment of resources, with some components that must have been obtained through trade, Dixon says. They also tell something about what mattered to their makers. "This is an organic artifact that really objectifies people's thoughts," he says. "You get these glimpses into people's minds that you could never get from just a stone arrowhead."

The oldest ice patch artifacts Dixon has found are about 3,000 years old, while Greg Hare has found a few objects that are about 9,000 years old. But it turns out Dixon's former student Craig Lee, now a research scientist at the Institute of Arctic and Alpine Research, has recovered the oldest ice patch artifact in the world.

Three years ago, Lee found the 10,300-year-old foreshaft of an atlatl dart in the mountains near Yellowstone National Park — far south of Alaska and the Yukon. Although Lee's find has not been widely publicized, Dixon says it confirms his conviction that ice patches and glaciers worldwide ought to be systematically surveyed before they disappear.

The past 20 years have also seen the discovery of eerily well-preserved frozen bodies in places as disparate as the Tyrolean Alps, the Andes and the mountains of northern British Columbia, Dixon notes. Recently, researchers have found Bronze Age artifacts high in the Swiss Alps and evidence of Viking reindeer-hunting parties in Norway.

Although Greg Hare agrees that more ice patch research is needed, he isn't sure whether the ice patches are shrinking as rapidly as he once feared.

His team has been taking careful measurements of ice fields each year, and so far the evidence is mixed. It could be that global climate change will bring greater snowfall to some mountain areas, even if temperatures grow warmer overall, he says.

"We've seen a reduction of the size of a number of the ice patches, but many of them have shown a pretty considerable reluctance to melt," he says. "The fact that they've been preserved for 9,000 years indicates that they're in a pretty protected environment."

Hare, meanwhile, believes the spate of ice patch discoveries point the way toward a new way of doing archaeology. "Rather than looking at the traditional low-lying areas, archaeologists are casting their eyes higher in the landscape and looking at mountain regions where there hadn't been a lot of activity before," he says. "People are seeing the ice melting and finding the presence of human use of the alpine that has been preserved for thousands of years."