By Sally Pobojewski
News and Information Services
Norse settlers living in doomed colonies on the coast of Greenland 500 years ago may have left clues to their mysterious disappearance in teeth from their graves. A U-M study of teeth from early Viking settlements appears to confirm the theory that rapidly cooling temperatures during the onset of a period called the Little Ice Age may have have been responsible for the demise of these colonies on Greenland around 1500 A.D.
“Analysis of oxygen isotope ratios of teeth from Norse [Viking] settlers and from native Inuits living in Greenland between 1100 and 1500 A.D. shows this was a time of declining temperatures,” said graduate student Henry C. Fricke. “Our data confirm historical records of the onset of the Little Ice Age in northern Europe—a period of cooler temperatures that lasted from about 1300 to 1850 A.D.”
Fricke and James R. O’Neil, professor of geological sciences, presented the results of their study—the first to use human teeth as an indicator of paleoclimatic change—at the Geological Society of America meeting held here Oct. 23–27.
The study is significant, not only because it offers new evidence on the frigid fate of Norse settlers, but also because it shows that human tooth enamel from archaeological sites provides a reliable record of temperature changes over time.
“This new tool gives us a means of studying how climate has changed in the relatively recent past, and will help us understand how climate could change in the future,” said O’Neil. “It will be especially valuable for studying climate variations in continental areas where humans have lived. Scientists have few well-constrained paleoclimatic indicators to work with in such regions.”
In their study, Fricke and O’Neil analyzed enamel from 29 human teeth excavated at three archaeological sites in Greenland and one in Denmark. At times, the Greenland sites were occupied by Norse settlers. At other times, the sites were occupied by people of the Thule culture—a term used by archaeologists to describe native Inuits living in Greenland after 1000 A.D.
The teeth were supplied by University of Copenhagen forensic anthropologists Neil Lynnerup and Anders Koch, who provided information on the archaeological context of the specimens and the approximate dates of occupation of the sites (1000 to 1850 A.D.).
The U-M geochemists determined that the ratio of oxygen isotopes in tooth enamel of a given population changes in response to local climate changes. Here’s how it works:
“The ratio of heavy (O-18) to light (O-16) isotopes in the calcium phosphate that comprises tooth enamel is directly related to this isotopic ratio in rain or snow falling on a local area, because the oxygen in this precipitation is incorporated into the tooth enamel of growing children who drink from local groundwater supplies like springs, lakes and rivers,” explained Fricke.
“The oxygen isotope ratio of rain and snowfall is, in turn, controlled by climatic factors, mostly temperature,” added O’Neil. “By tracking changes in isotopic ratios, we can determine the rate and direction of temperature changes in a given area, perhaps at a resolution of several decades, depending on the accuracy of the dating. At present, our estimates of the changes in temperature are more reliable than the changes themselves.”
Although using teeth from archaeological sites as a paleoclimatic indicator will open up new research possibilities to scientists, it has some limitations, according to Fricke. “To analyze enamel, we must destroy the tooth,” he said. “It takes a lot of convincing to persuade anthropologists to donate material that will be destroyed in the analysis.”
In addition, the ability to resolve climate change in a given area depends totally on how accurately the archaeological material can be dated. This problem limits the resolution of the samples already analyzed from Greenland and Denmark to only hundreds of years, but Fricke and O’Neil are optimistic that more accurately dated specimens will be forthcoming from their Danish colleagues.
“Ideally we would like to have several precisely dated groups of teeth from archaeological sites in one geographic area like the North Atlantic,” said Fricke. “With isotopic data for such specimens, we could produce maps of temperature changes over time for different portions of the globe.”
In an interesting future spin-off of their study, O’Neil and Fricke plan to measure the oxygen isotope ratios of teeth from 17 individuals buried in a mass grave near one of the Greenland sites. “Human teeth provide an isotopic signature of a person’s origin,” O’Neil said. “It should be possible to identify these individuals as either native Greenlanders or Europeans who perhaps were killed in a shipwreck.”
Specimens examined in the U-M study were analyzed at the U-M Stable Isotope Laboratory—one of only about six laboratories in the world where oxygen isotope analyses of this type of material is being done. The research was funded by the National Science Foundation.
