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 (δ18OPO4) and compared patterns to interpolated and measured yearly variation in environmental waters as well as from sagebrush leaves, lakes, and rivers (δ18Ow). 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 δ18Ow values into expected δ18OPO4* values (δ18OW‐PO4*). Pronghorn δ18OPO4 values from tooth enamel record nearly the full amplitude of seasonal variation from Wyoming δ18OW‐PO4* values. Furthermore, pronghorn enamel δ18OPO4 values are more similar to modeled δ18OW‐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 δ18OPO4 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.
Highlights
Today, climate can be measured at a range of spatiotemporal scales through assessment of stable isotope ratios in precipitation (δ18O, δ2H; Bailey et al, 2019; Daniels et al, 2017; Liu et al, 2014; Vachon et al, 2010a; Welker, 2012)
Because the interpolated δ18Ow values are based in large part on the USNIP δ18Ow data for nine Wyoming sites, they unsurprisingly fall within the range of yearly, monthly, and spatial variation of the actual measured values
In all but one case, we find that pronghorn bone δ18OPO4 values are biased toward values typical of the spring and summer, suggesting greater mineralization of bone during these months and reduction of bone remodeling during the winter months (Figure 2)
Summary
Climate can be measured at a range of spatiotemporal scales through assessment of stable isotope ratios in precipitation (δ18O, δ2H; Bailey et al, 2019; Daniels et al, 2017; Liu et al, 2014; Vachon et al, 2010a; Welker, 2012). An array of other climate proxies have been applied to paleoclimate reconstruction in deeper time, including stable isotope analysis (δ18O, δ13C) of animal hard tissues, paleosols, leaf waxes, and diatoms from lake sediments (Bailey et al, 2018; Clementz, 2012; Daniels et al, 2017; Fox et al, 2012; Green et al, 2018; Koch, 2007; Kohn & Cerling, 2002; Kohn & Dettman, 2007; Macfadden, 2000; Stevenson et al, 2010), physical properties of paleosols (i.e., depth to the calcic horizon; Cerling et al, 1989; Retallack, 2001; Sheldon & Tabor, 2009; Stevenson et al, 2010), leaf morphology (Dunn et al, 2015; Wilf, 1997), and vertebrate community structure (Eronen et al, 2010; Fortelius et al, 2002; Fraser & Theodor, 2013) These paleoclimate proxies are used to estimate mean annual temperatures, mean annual precipitation, vegetation structure, validate climate models, and contextualize studies of paleodiversity (Cullen et al, 2020; Fraser et al, 2014; Rose et al, 2011), but paleoclimate proxies vary considerably in their fidelity to climate, preservation potential, and spatiotemporal resolution (Axford et al, 2011). Choice of proxy should be determined by availability in the fossil record and efficacy as established by modern validation studies
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
