ANNUAL-SCALE ANALYSIS OF CLIMATE CHANGE FROM GLACIAL TO MODERN TIMES IN NORTH AMERICA USING SERIAL ISOTOPIC ANALYSIS OF MOLARS OF HYPSODONT MAMMALS

The environmental transition from the most recent global glacial event to the modern climate regime has been investigated and described using floral and faunal analysis of dated fossil localities and packrat middens, as well as computerized climate modeling. These models are used with confidence for understanding centennial- or longer-scale general patterns of climate over the last 20,000 years. Techniques involving the use of stable isotopes from tooth enamel are rapidly becoming a common method used to examine similar general patterns of climate in situations where other proxies may not be available. With serial sampling of molar teeth of hypsodont mammals, it is now possible to look at annual-scale patterns of climate change during the transition from glacial to modern times, and compare this with prior models. There has been discussion about the validity of such studies, due to the variety of techniques available and the sensitivity of isotopic proxies to such events as summertime precipitation, altitude effects, animal migration, and alteration of the isotopic signature during the fossilization process. We show here that the interpretations based upon serial isotopic analysis, when made understanding possible alterations of the isotopic signal, agree with previous models of climate change from glacial to modern times, with the additional benefit of providing shorter time-scale information about climatic events. This suggests that with similar studies using fossils, in situations where floral and faunal analyses are not helpful or computer models are not available, we can still learn a great deal about annual climatic variation in the remote past.