Pulling Teeth to Analyze Climate Change
Northern scientists who study climate change today often use innovative techniques to determine an area's temperature centuries ago. Pictures of ancient weather often are painted by those analyzing polar ice cores, sea floor sediments and permafrost. But few researchers have been as ingenious as those at the University of Michigan; they're literally pulling teeth--ancient Viking teeth--to come up with a new way to figure out old weather patterns.
Spurred on by the knowledge that tooth enamel contains information that can be directly correlated to drinking water, University of Michigan geochemist James O'Neil and graduate student Henry Fricke recently used 29 teeth found in remains at ancient Norse colonies to confirm a local temperature decrease at the onset of the medieval Little Ice Age, hundreds of years ago.
University of Copenhagen anthropologists gave O'Neil and Fricke the teeth, which originally belonged to Vikings and Inuit Eskimos who lived at three sites in Greenland and one area in Denmark between 1100 and 1500 AD. The researchers examined the hard enamel layer on the outside of the ancient teeth to determine an isotope useful in assessing climate change. Studies on modern animals show a direct correlation between the oxygen isotope ratio of tooth enamel to the oxygen isotope ratio of water animals drank while their secondary teeth were forming.
The oxygen isotope ratio of water also is used by polar ice corers, permafrost specialists and others to study climate change. According to John Kelley with the University of Alaska Fairbanks' Polar Ice Coring Office, different oxygen molecules found in water have different molecular weights. Lighter isotopes, such as oxygen-16, form in warmer conditions; when they are compared with the heavier isotope oxygen-18, for example, researchers can determine the temperature of the air when the water being sampled fell as precipitation.
O'Neil and Fricke were able to determine the ratio of oxygen-16 to oxygen-18 after chipping pieces of enamel off Viking teeth and dissolving those pieces in nitric acid. The ratio enabled the researchers to determine the relative temperature change of air during ancient rains and snow falls. That precipitation fed the springs, rivers and lakes that quenched the thirst of Vikings and Inuits, whose tooth enamel absorbed the oxygen while they grew.
After comparing teeth of different ages, the scientists found that the average temperature dropped about 1.5 degrees Celsius between 1100 AD and 1400 AD. Some anthropologists theorize that the temperature change was great enough to cause the mysterious disappearance of the Norsemen colony in Greenland in the late 1400's. Fricke speculates that the colder temperatures may have forced food animals, such as whales and seals, to migrate south. Cooler weather also may have caused increasingly large icebergs to form, hampering shipping between Greenland and Iceland.
Kelley said the researchers' findings are consistent with the onset of a cooling period known as the Little Ice Age in Northern Europe. The temperature decrease at that time could have caused crops to fail and new glaciers to form, which might have inspired the Norse settlers to move away from their homelands.
O'Neil and Fricke's method of measuring the oxygen isotope ratio hidden in human teeth could prove to be an important part of the global climate change puzzle, especially in areas that don't contain permafrost, sea ice or other features traditionally studied by ancient weather experts.
The method does require scientists to destroy the ancient teeth, however, so it will probably be used sparingly. Anthropologists are understandably hesitant to give researchers their best specimens.
"When we first started, we were likely to get a tooth that had been rolling around in a box for a while," Fricke said. "But it's really just starting to hit anthropologists that these destructive techniques help them gain a lot of information."
