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Treasure hunters feel pull of magnetic gear

Archaeologists are used to digging. Now they're finding it easier to follow magnetic fields to hidden artifacts. Photos: Hunting for buried treasure

Magnets may be a staple of New Age mysticism, but a magnetometer might just lead a Silicon Valley entrepreneur to a centuries-old treasure.

That entrepreneur and a group of archaeologists hope to uncover an unusual haul off the coast of Mexico: a cache of Ming pottery that's more than 400 years old, sitting in the hull of a Spanish galleon.

In the late 1500s, a Spanish trading ship set sail from Manila, Philippines--but it never arrived at its intended destination in Acapulco. The vessel capsized off the west coast of Mexico. In recent years, antique pottery shards have been found on a strip of Mexican beach many miles long. But the bulk of the cargo remains hidden, probably in the ocean.

Now, by using a magnetometer--an instrument that measures the magnetic pull of a given area--the researchers hope to locate the cargo precisely. They expect to find some of the cargo and the hull largely in the same condition they were in when the ship sank, preserved by local environmental conditions.

The magnetometer "looks like a beer can on a broomstick," said Sheldon Breiner, a geophysicist and explorer and a principal at New Ventures West.

For Breiner, the expedition is as much about history as it is about tinkering with instruments he has spent decades honing for oil and mineral exploration. An expert in such magnetic devices, Breiner developed one of the first gun detectors in the wake of the assassination of Robert F. Kennedy. A Howard Hughes-owned company asked him to create a system for finding manganese nodules in the ocean--though as it turned out, the effort in reality was a CIA-sponsored project to find a lost Russian sub. Breiner has also helped found a few companies, including Geometrics, which makes the magnetometer he uses.

In the mid-1960s, Breiner and his magnetometer helped find what could be the remnants of the buried Greek city of Sybaris. The success of that project led a few years later to a dig in Mexico with noted Yale archeologist Michael Coe that unearthed scores of colossal Olmec carved stone monuments. Among them was a 10-ton sculpture of a head dating back 3,000 years, one of the oldest monument finds in the Western hemisphere.

"It was one of the easiest projects I had anywhere," said Breiner, explaining that the buried monuments were in a flood plain of generally nonmagnetic materials that contained very little residue of modern human habitation. "All the monuments were carved out of a quarry 50 kilometers away. Any rock in the area was magnetic and brought there by man--for us to discover millennia later."

How it works
A magnetometer essentially reads the magnetic properties of the ground--like a supersensitive compass. The measurements are then compiled into a magnetic map in conjunction with Global Positioning System data.

"It is not great to use in a lab next to a piece of steel," Breiner said. "It is for low-intensity fields with high precision...outdoors. You map the rocks you can't see, usually for looking for oil or minerals."

Since 1945, archaeologists have adopted a variety of geophysical technologies--electrical probes, seismic reflection tools and radar--to help reduce the hours they spend digging, as well as keep sites better preserved. One of the more commonly used applications of a magnetometer is a ground-probing radar device, which looks something like a lawn mower.

Magnetic detection is handy because nearly everything in the ground contains the mineral magnetite. Even bacteria from the detritus of human habitation produce it--always in varying degrees. Sudden contrasts point to sites of possible human habitation.

"In archaeology, magnetometers are used a great deal. We use it mostly on land-based sites, such as to detect Native American villages or burn sites," said Kenneth Kvamme, associate professor of archaeology at the University of Arkansas. "It would be particularly effective on a shipwreck because of the iron anchors, cannons, spikes."

What's next
Unlike the Olmec site, the shipwreck off the coast of Mexico has, in some ways, already been discovered. The locals have found Chinese pottery shards on the beach for years, which has prompted some to claim that the Chinese visited Mexico, Breiner said.

He can't be precise about where the pottery has been found because terms of a permit from the government that prevents the archaeologists from publicly revealing the location.

Last year, the archeological team visited the site and came away with a wealth of artifacts: complete Ming-era bowls, large pieces of terra cotta urns, hunks of beeswax and the remnants of a canoe close to 1,000 years old.

Cruising with the magnetometer in the adjacent waters, the team has found a magnetic anomaly--which possibly represents the ship itself. In April, the group will conduct a preliminary investigation of the underwater site. If successful, the next stage will involve amassing funds for a complete dig.

Treasure hunting, however, has its share of false leads. The strong underground readings the group found may just be anchors from a modern ship, Breiner said.