Pronghorn (Antilocapra americana) enamel phosphate δ18O values reflect climate seasonality: Implications for paleoclimate reconstruction

Danielle Fraser; Sora L Kim; Jeffrey M Welker; Mark T Clementz

doi:10.1002/ece3.8337

Pronghorn (Antilocapra americana) enamel phosphate δ¹⁸O values reflect climate seasonality: Implications for paleoclimate reconstruction

Ecol Evol. 2021 Nov 23;11(23):17005-17021. doi: 10.1002/ece3.8337. eCollection 2021 Dec.

Authors

Danielle Fraser^{1

2

3

4

5}, Sora L Kim^{5

6}, Jeffrey M Welker^{7

8

9}, Mark T Clementz^{5

10}

Affiliations

¹ Palaeobiology Canadian Museum of Nature Ottawa ON Canada.
² Department of Biology Carleton University Ottawa ON Canada.
³ Department of Earth Sciences Carleton University Ottawa ON Canada.
⁴ Department of Paleobiology Smithsonian Institution National Museum of Natural History Washington District of Columbia USA.
⁵ Department of Geology and Geophysics University of Wyoming Laramie Wyoming USA.
⁶ Department of Life and Environmental Sciences University of California Merced California USA.
⁷ Department of Biological Sciences University of Alaska Anchorage Anchorage Alaska USA.
⁸ Department of Ecology and Genetics University of Oulu Oulu Finland.
⁹ UArctic Oulu Finland.
¹⁰ Program in Ecology University of Wyoming Laramie Wyoming USA.

Abstract

Stable oxygen isotope (δ¹⁸O) compositions from vertebrate tooth enamel are widely used as biogeochemical proxies for paleoclimate. However, the utility of enamel oxygen isotope values for environmental reconstruction varies among species. Herein, we evaluate the use of stable oxygen isotope compositions from pronghorn (Antilocapra americana Gray, 1866) enamel for reconstructing paleoclimate seasonality, an elusive but important parameter for understanding past ecosystems. We serially sampled the lower third molars of recent adult pronghorn from Wyoming for δ¹⁸O in phosphate (δ¹⁸O_PO4) and compared patterns to interpolated and measured yearly variation in environmental waters as well as from sagebrush leaves, lakes, and rivers (δ¹⁸O_w). As expected, the oxygen isotope compositions of phosphate from pronghorn enamel are enriched in ¹⁸O relative to environmental waters. For a more direct comparison, we converted δ¹⁸O_w values into expected δ¹⁸O_PO4* values (δ¹⁸O_W-_PO4*). Pronghorn δ¹⁸O_PO4 values from tooth enamel record nearly the full amplitude of seasonal variation from Wyoming δ¹⁸O_W-PO4* values. Furthermore, pronghorn enamel δ¹⁸O_PO4 values are more similar to modeled δ¹⁸O_W-PO4* values from plant leaf waters than meteoric waters, suggesting that they obtain much of their water from evaporated plant waters. Collectively, our findings establish that seasonality in source water is reliably reflected in pronghorn enamel, providing the basis for exploring changes in the amplitude of seasonality of ancient climates. As a preliminary test, we sampled historical pronghorn specimens (1720 ± 100 AD), which show a mean decrease (a shift to lower values) of 1-2‰ in δ¹⁸O_PO4 compared to the modern specimens. They also exhibit an increase in the δ¹⁸O amplitude, representing an increase in seasonality. We suggest that the cooler mean annual and summer temperatures typical of the 18th century, as well as enhanced periods of drought, drove differences among the modern and historical pronghorn, further establishing pronghorn enamel as excellent sources of paleoclimate proxy data.

Keywords: oxygen stable isotopes; palaeoclimate; pronghorn; seasonality.