An official website of the United States government
Variability of oxygen isotopes in environmental water is recorded in tooth enamel, providing a record of seasonal change, dietary variability, and mobility. Physiology dampens this variability, however, as oxygen passes from environmental sources into blood and forming teeth. We showcase two methods of high resolution, 2-dimensional enamel sampling, and conduct modeling, to report why and how environmental oxygen isotope variability is reduced in animal bodies and teeth. First, using two modern experimental sheep, we introduce a sampling method, die-saw dicing, that provides high-resolution physical samples (n = 109 and 111 sample locations per tooth) for use in conventional stable isotope and molecular measurement protocols. Second, we use an ion microprobe to sample innermost enamel in an experimental sheep (n = 156 measurements), and in a Pleistocene orangutan (n = 176 measurements). Synchrotron and conventional μCT scans reveal innermost enamel thicknesses averaging 18 and 21 μm in width. Experimental data in sheep show that compared to drinking water, oxygen isotope variability in blood is reduced to 70–90 %; inner and innermost enamel retain between 36 and 48 % of likely drinking water stable isotope range, but this recovery declines to 28–34 % in outer enamel. 2D isotope sampling suggests that declines in isotopic variability, and shifted isotopic oscillations throughout enamel, result from the angle of secretory hydroxyapatite deposition and its overprinting by maturation. This overprinting occurs at all locations including innermost enamel, and is greatest in outer enamel. These findings confirm that all regions of enamel undergo maturation to varying degrees and confirm that inner and innermost enamel preserve more environmental variability than other regions. We further show how the resolution of isotope sampling — not only the spatial resolution within teeth, but also the temporal resolution of water in the environment — impacts our estimate of how much variation teeth recover from the environment. We suggest inverse methods, or multiplication by standard factors determined by ecology, taxon, and sampling strategy, to reconstruct the full scale of seasonal environmental variability. We advocate for combined inverse modeling and high-resolution sampling informed by the spatiotemporal pattern of enamel formation, and at the inner or innermost enamel when possible, to recover seasonal records from teeth.
more »
« less
Fine-scaled climate variation in equatorial Africa revealed by modern and fossil primate teeth
Variability in resource availability is hypothesized to be a significant driver of primate adaptation and evolution, but most paleoclimate proxies cannot recover environmental seasonality on the scale of an individual lifespan. Oxygen isotope compositions (δ 18 O values) sampled at high spatial resolution in the dentitions of modern African primates ( n = 2,352 near weekly measurements from 26 teeth) track concurrent seasonal precipitation, regional climatic patterns, discrete meteorological events, and niche partitioning. We leverage these data to contextualize the first δ 18 O values of two 17 Ma Afropithecus turkanensis individuals from Kalodirr, Kenya, from which we infer variably bimodal wet seasons, supported by rainfall reconstructions in a global Earth system model. Afropithecus ’ δ 18 O fluctuations are intermediate in magnitude between those measured at high resolution in baboons ( Papio spp.) living across a gradient of aridity and modern forest-dwelling chimpanzees ( Pan troglodytes verus ). This large-bodied Miocene ape consumed seasonally variable food and water sources enriched in 18 O compared to contemporaneous terrestrial fauna ( n = 66 fossil specimens). Reliance on fallback foods during documented dry seasons potentially contributed to novel dental features long considered adaptations to hard-object feeding. Developmentally informed microsampling recovers greater ecological complexity than conventional isotope sampling; the two Miocene apes ( n = 248 near weekly measurements) evince as great a range of seasonal δ 18 O variation as more time-averaged bulk measurements from 101 eastern African Plio-Pleistocene hominins and 42 papionins spanning 4 million y. These results reveal unprecedented environmental histories in primate teeth and suggest a framework for evaluating climate change and primate paleoecology throughout the Cenozoic.
more »
« less
- PAR ID:
- 10391368
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 35
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
IntroductionAstarte borealisholds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates ofA. borealisin some locations (<0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ18O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ18Owatervalues. MethodsHere we use secondary ion mass spectrometry (SIMS) to microsample anA. borealisspecimen from the southern Baltic Sea, yielding 451 SIMS δ18Oshellvalues at sub-monthly resolution. ResultsSIMS δ18Oshellvalues exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001. DiscussionAge-modeled SIMS δ18Oshellvalues correlate significantly with bothin situtemperature measured from shipborne CTD casts (r2 = 0.52, p<0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r2 = 0.42, p<0.001). We observe the strongest correlation between SIMS δ18Oshellvalues and salinity when both datasets are run through a 36-month LOWESS function (r2 = 0.71, p < 0.001). Similarly, we find that LOWESS-smoothed SIMS δ18Oshellvalues exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r2 = 0.46, p<0.001). Change point analysis supports that SIMS δ18Oshellvalues capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ18Oshelltime series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ18Owatervalues on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ18Oshellvalues inA. borealisshells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales.more » « less
-
Abstract Eocene climate cooling, driven by the fallingpCO2and tectonic changes in the Southern Ocean, impacted marine ecosystems. Sharks in high‐latitude oceans, sensitive to these changes, offer insights into both environmental shifts and biological responses, yet few paleoecological studies exist. The Middle‐to‐Late Eocene units on Seymour Island, Antarctica, provide a rich, diverse fossil record, including sharks. We analyzed the oxygen isotope composition of phosphate from shark tooth bioapatite (δ18Op) and compared our results to co‐occurring bivalves and predictions from an isotope‐enabled global climate model to investigate habitat use and environmental conditions. Bulk δ18Opvalues (mean 22.0 ± 1.3‰) show no significant changes through the Eocene. Furthermore, the variation in bulk δ18Opvalues often exceeds that in simulated seasonal and regional values. Pelagic and benthic sharks exhibit similar δ18Opvalues across units but are offset relative to bivalve and modeled values. Some taxa suggest movements into warmer or more brackish waters (e.g.,Striatolamia,Carcharias) or deeper, colder waters (e.g.,Pristiophorus). Taxa likeRajaandSqualusdisplay no shift, tracking local conditions in Seymour Island. The lack of difference in δ18Opvalues between pelagic and benthic sharks in the Late Eocene could suggest a poorly stratified water column, inconsistent with a fully opened Drake Passage. Our findings demonstrate that shark tooth bioapatite tracks the preferred habitat conditions for individual taxa rather than recording environmental conditions where they are found. A lack of secular variation in δ18Opvalues says more about species ecology than the absence of regional or global environmental changes.more » « less
-
Abstract Tropical Pacific seawater and precipitation stable oxygen isotope data aid in understanding modern oceanic and atmospheric interactions, and these data are particularly valuable as they are archived in isotope‐based paleoclimate records. However, the absence of modern seawater isotope time series limits the ability to identify the atmospheric influences on these data, precluding robust paleoclimate interpretations. We present a new 10 year sub‐monthly record of seawater and precipitation stable oxygen isotope values (δ18Oswand δ18Op) from Koror, Palau. Our dataset indicates that temporally, δ18Oswis strongly influenced by local δ18Op.Both monthly δ18Oswand δ18Opare highly correlated with outgoing longwave radiation across the tropical Pacific, reflecting a Walker Circulation imprint on the surface ocean. Changes in the Palau δ18Osw—salinity relationship correspond to NINO3.4 variability, indicating a difference in how these variables record El Niño Southern Oscillation (ENSO) information, but demonstrating the utility of δ18Oswto reconstruct ENSO variability in the western tropical Pacific.more » « less
-
Abstract The National Ecological Observatory Network (NEON) provides open-access measurements of stable isotope ratios in atmospheric water vapor (δ 2 H, δ 18 O) and carbon dioxide (δ 13 C) at different tower heights, as well as aggregated biweekly precipitation samples (δ 2 H, δ 18 O) across the United States. These measurements were used to create the NEON Daily Isotopic Composition of Environmental Exchanges (NEON-DICEE) dataset estimating precipitation (P; δ 2 H, δ 18 O), evapotranspiration (ET; δ 2 H, δ 18 O), and net ecosystem exchange (NEE; δ 13 C) isotope ratios. Statistically downscaled precipitation datasets were generated to be consistent with the estimated covariance between isotope ratios and precipitation amounts at daily time scales. Isotope ratios in ET and NEE fluxes were estimated using a mixing-model approach with calibrated NEON tower measurements. NEON-DICEE is publicly available on HydroShare and can be reproduced or modified to fit user specific applications or include additional NEON data records as they become available. The NEON-DICEE dataset can facilitate understanding of terrestrial ecosystem processes through their incorporation into environmental investigations that require daily δ 2 H, δ 18 O, and δ 13 C flux data.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.2123366119
