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David Robinson discussed a sediment core taken from the Massachusetts seabed.
David Robinson discussed a sediment core taken from the Massachusetts seabed. (Stew Milne for the Boston Globe)

Sunken treasure

Scientists find evidence of ancient forest buried under the seabed of Nantucket Sound

Scientists mapping the seabed under a proposed wind farm in Nantucket Sound were stunned by their find: evidence of a submerged forest under 6 feet of mud.

It's hardly the lost city of Atlantis, but the piece of birch wood, the yellowish-green grass, soil, and insect parts appear to be part of a forest floor that lined the coastline 5,500 years ago, before being swallowed by the sea that rose after the last ice age. Nearby is evidence of a drowned kettle pond and marsh.

The find has scientists abuzz because if a preserved forest rests below the sea, maybe artifacts from ancient cultures do, too -- items that could help answer some of the most vexing questions about early people in North America. As more energy projects are proposed off New England, archaeologists say, there will be more opportunity for even bigger finds.

''We've been arguing for years whether there are remnant prehistoric landscapes out there and now we know they can exist," said Victor Mastone, director and chief archaeologist of the Massachusetts Board of Underwater Archaeological Resources. ''This means there is the potential to go after the big theory of how did people get here and how they lived."

Cape Wind Associates, which has proposed the wind farm, redesigned the 130-turbine project this year to avoid the discovered area.

So much of the world's water was locked up in glaciers during the ice age, ocean levels plummeted at least 300 feet. New England's continental shelf was exposed and in some places, the coastline extended more than 75 miles from its current location.

Even at the end of the ice age 10,000 years ago, when melting glaciers were causing sea levels to rapidly rise, New England's coastline -- etched with river valleys, forests, and lakes -- stretched miles farther than today.

The earliest evidence of Native Americans in New England has come from around this time -- a period when hunters could have walked from Falmouth to Nantucket.

Tantalizing clues to these times have been extracted from the sea. New England fishermen have hauled up wooly mammoth and mastodon teeth dozens of miles from shore. A Native American campsite was found on the banks of a submerged riverbed off Maine's Deer Isle. At Odiorne Point State Park in Rye, N.H., visitors at low tide can still find tree stumps and roots dating back almost 4,000 years.

But these finds have little archaeological context. Scientists say the mastodon and mammoth teeth could have been swept out to sea by currents. The Native American campsite was so eroded it was difficult to extract a detailed story of the time period. And if any submerged settlements were at the Rye Beach drowned forest, erosion washed them away.

''That's why the Nantucket Sound site is important," said David Robinson, senior underwater archaeologist for The Public Archaeology Laboratory Inc. in Pawtucket, R.I. He discovered the Nantucket Sound site two years ago.

''It provides evidence to say these land forms can survive," he said.

Through several sediment samples taken 30 to 50 feet below the water's surface east of Horseshoe Shoal, Robinson pieced together the ancient landscape. The birch wood retrieved from the site is only about 4 inches long and 2 inches in diameter. But the delicate root hairs, leaf pieces and seeds in the samples tell Robinson and other scientists that the area probably was entombed under mud, and thus kept safe from stormy seas and tides.

''We really don't know how big the area is . . . although there is some evidence is it is not tiny," said John King, a professor of oceanography at the University of Rhode Island who has helped Robinson analyze the samples. King said that if Native American cultural sites are to be found, an intact landscape has to be found first. ''You need to zero in on these places. Without narrowing down the haystack you are not going to find anything."

The Native American story in New England and North America is incomplete. Archaeologists have long believed the first humans came to this continent about 12,000 years ago via a land bridge from Siberia to Alaska, following mammoths and other big game through the Great Plains, then farther east and south. But some scientists have put forth a different, controversial, theory: People migrated on a coastal route on the edge of the frozen north to get from Russia to the Pacific Coast -- or from Europe to North America.

With the prehistoric shoreline under water, there has been little evidence to support the coastal hypothesis. If scientists find an intact underwater cultural site -- in Nantucket Sound or elsewhere -- it might provide evidence of tools or food gathering that could help settle the debate.

Some scientists, however, say it's a fool's errand: Finding submerged settlements is so hard it's not worth the enormous time and expense.

''Most of the finds on land are fortuitous," said Robert Oldale, geologist emeritus of the US Geological Survey in Woods Hole, who has spent decades looking at the geology of Cape Cod's continental shelf. ''When you go offshore, it's thousands of times tougher."

Robinson, who worked on excavating submerged Stone-Age settlements off Denmark this fall, said that once a site is found, it's no more difficult to excavate than a shipwreck. The sea's cold temperatures and lack of oxygen preserve items far better than conditions on land. Denmark's finds have included fabric and food residue in ceramic pots in waters similar in condition to those off New England.

Archaeologists say the increase in projects off New England could help uncover sites of submerged settlements.

As with projects on land, federal and state laws require offshore projects to hire archaeological companies to determine whether construction will harm historically significant remains. Cape Wind hired The Public Archaeology Laboratory.

Historically, these underwater searches only meant one thing: shipwrecks. But technology is advancing to detect solid land below sea mud and sand, as is expertise around the world to excavate these sites. At Robinson's suggestion, officials at Stellwagen Bank National Marine Sanctuary -- which protects a once-exposed plateau 25 miles off Boston -- is considering special protection for paleontological resources in a new management plan it is drafting.

Robinson isn't sure when he'll study the Nantucket Sound site further. The area is difficult to dive and there is no money for surveying. But he's finishing his doctorate on these types of sites, and once he gets better data about underwater landscapes, he will start looking for drowned riverbanks because he knows Native American sites on land have been found on riverbanks. He hopes to one day take a magnetic sensor over potential areas, where ancient hearths will give off a telltale ping.

If Robinson does find a site, he will use the same archaeological tools used to research underwater shipwrecks to scrape and brush away the seabed.

Divers can dig excavation test pits with a water dredge, which gently vacuums sediment from the sea floor in layers to capture artifacts in a mesh bag.

''We would go slowly and methodically, just like we would do on land," he said. ''Everyone has always said this is impossible. It's not. It just requires a different way of approaching the problem."

Beth Daley can be reached at

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