The University Record, November 13, 1995

Careful sampling and interpretation required for oxygen isotope technique

By Sally Pobojewski
News and Information Services

U-M geochemists caution that a promising new paleoclimatological research technique, which uses the stable isotope chemistry of mammalian tooth enamel to determine past climate changes, may be much more complicated than researchers initially believed.

According to Henry C. Fricke, graduate student in geochemistry, the handful of researchers working in this field generally have operated under the assumption that changes in the oxygen isotope ratio of tooth enamel were caused only by changes in local climate---primarily temperature variations over extended periods of time.

In a recent detailed analysis of bison teeth from a 500-year-old archaeological site in Wyoming and teeth from a domesticated modern sheep living on a California ranch, however, Fricke and James R. O'Neil, professor of geological sciences, observed that the oxygen isotope ratio can vary significantly between teeth---and even within a single tooth---from the same animal.

"For a given deposit, seasonal climate changes, the animal's season of birth, and its behavioral patterns all can cause large inter- and intra-tooth variations in the oxygen isotope ratio of tooth enamel," Fricke says. "Unless scientists are aware of these factors, they may draw the wrong conclusions from their data."

Fricke and O'Neil presented the results of their study at the Geological Society of America meeting held in New Orleans Nov. 6-9.

The research project was funded by the National Science Foundation.