Patterns of climate and C4 plant abundance in the southwestern United States during the last glaciation were evaluated from isotopic study of herbivore tooth enamel. Enamel δ13C values revealed a substantial eastward increase in C4 plant consumption for Mammuthus spp., Bison spp., Equus spp., and Camelops spp. The δ13C values were greatest in Bison spp. (-6.9 to + 1.7‰) and Mammuthus spp. (-9.0 to +0.3‰), and in some locales indicated C4-dominated grazing. The δ13C values of Antilocaprids were lowest among taxa (-12.5 to -7.9‰) and indicated C3 feeding at all sites. On the basis of modern correlations between climate and C4 grass abundance, the enamel data imply significant summer rain in parts of southern Arizona and New Mexico throughout the last glaciation. Enamel δ18O values range from +19.0 to +31.0‰ and generally increase to the east. This pattern could point to a tropical or subtropical source of summer rainfall. At a synoptic scale, the isotope data indicate that interactions of seasonal moisture, temperature, and lowered atmospheric pCO2 determined glacial-age C4 abundance patterns.
- Last glaciation
- United States
- Vegetation history
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Earth-Surface Processes
- Earth and Planetary Sciences(all)