Eocene-Oligocene Latitudinal Climate Gradients in North America Inferred from Stable Isotope Ratios in Perissodactyl Tooth Enamel

Authors

Alessandro Zanazzi, Utah Valley University
Emily Judd, Utah Valley University
Andrew Fletcher, Utah Valley University
Harold Bryant, Royal Saskatchewan Museum
Matthew J. Kohn, Boise State UniversityFollow

Document Type

Article

Publication Date

10-25-2014

Abstract

The Eocene-Oligocene transition (~ 34 Ma) was one of the most pronounced episodes of climate change of the Cenozoic. In order to investigate this episode of global climate cooling in North America, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl (horse and rhino) tooth enamel samples from the Eocene-Oligocene rocks of the Cypress Hills Formation (southwestern Saskatchewan, Canada); we then compared the results with previously published data from the US Great Plains (Nebraska, South Dakota, and Wyoming).

Average (± 1σ) perissodactyl enamel δ¹³C values (vs. V-PDB) in the Eocene (-8.8 ± 0.3‰) and Oligocene (-9.0 ± 0.3‰) are indistinguishable, suggesting no major change in mean annual precipitation in Saskatchewan across the transition. The δ¹³C values in Saskatchewan indicate the presence of arid ecosystems and are slightly higher than those in the US Great Plains, suggesting drier conditions at higher latitudes. With respect to oxygen isotopes, average (± 1σ) perissodactyl enamel δ¹⁸O values (vs. V-SMOW) in the Eocene (19.8 ± 2.0‰) and Oligocene (20.1 ± 3.6‰) are also indistinguishable, suggesting no change in the δ¹⁸O of meteoric precipitation across the transition in Saskatchewan. Enamel δ¹⁸O variability is much larger in the Oligocene vs. Eocene, indicating a large increase in temperature seasonality. This increase in enamel δ¹⁸O variability is much larger than that recorded in the US Great Plains, suggesting that higher latitudes are more sensitive to major episodes of climate change with respect to temperature seasonality. Finally, our data indicate no major change in the Oligocene vs. Eocene latitudinal gradient in local water δ¹⁸O in North America, which suggests no change in mean annual temperature gradients across the transition. This result supports the hypothesis that ascribes the climate change of the transition with a drop in atmospheric pCO₂ because climate models show that this mechanism produces uniform cooling at mid-latitudes.

Copyright Statement

NOTICE: this is the author’s version of a work that was accepted for publication in Palaeogeography, Palaeoclimatology, Palaeoecology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Palaeogeography, Palaeoclimatology, Palaeoecology, (In Press) doi: 10.1016/j.palaeo.2014.10.024

Publication Information

Zanazzi, Alessandro; Judd, Emily; Fletcher, Andrew; Bryant, Harold; and Kohn, Matthew J.. (2014). "Eocene-Oligocene Latitudinal Climate Gradients in North America Inferred from Stable Isotope Ratios in Perissodactyl Tooth Enamel". Palaeogeography, Palaeoclimatology, Palaeoecology, . https://doi.org/10.1016/j.palaeo.2014.10.024