Viking teeth recount sad Greenland tale.

Although 500-year-old corpses can't describe their deaths, geochemists have found a way to pull vital clues directly from the mouths of ancient Norsemen whose colony in Greenland thrived for centuries before disappearing mysteriously in the late 1400s. Studies of oxygen locked within the enamel of the Viking teeth reveal that Greenland's once balmy climate turned frigid, sealing the colony's fate.

Henry C. Fricke of the University of Michigan in Ann Arbor and his colleagues are the first researchers to decipher information about past climates using isotopic evidence from human bodies. While geochemists often use oxygen isotopes to reconstruct conditions, they typically analyze oxygen from nonbiological materials such as seafloor sediments, soils, or ancient ice.

"People are interested in humans and their relationship to climate change. If this technique works, it tells what kind of climate the humans lived under because the evidence comes directly from the humans," comments Paul Koch of Princeton University.

Fricke and his colleagues tried the technique because previous studies on modern animals had shown that tooth enamel records the ratio of oxygen-18 to oxygen-16 in precipitation consumed by the animals during their formative years. The isotopic ratio, in turn, indicates the local temperature.

Fricke and his coworkers looked at 29 teeth uncovered at three archeological sites in Greenland and one in Denmark. To test the technique, they documented that the isotopic ratios varied as expected with latitude. Next, the researchers looked at how ratios changed over time in southern Greenland. By comparing teeth from the year 1100 with those from 1450, they found that mean annual temperatures dropped by about 1.5[degrees]C, which would have had significant effects, says Fricke. They reported their findings late last month at a meeting of the Geological Society of American in Seattle.

The tooth study corroborates other evidence linking climate to the demise of the Norsemen on Greenland. The colony had flourished during the first few centuries of this millennium, but a cooling in the 1300s and an increase in icebergs hampered shipping between Greenland and Iceland, ultimately cutting off contact with Greenland. Historians believe that the colder temperatures brought food and fuel shortages. When ships again reached Greenland in the late 1400s, no living colonists remained, says Fricke.

Climate may not have worked alone, however. As the region cooled, northern Inuit moved into the Europeans' territory. Anthropologists have wondered whether conflict with the Inuit helped extinguish the Norse colony.