Nitrogen palaeo-isoscapes: Changing spatial gradients of faunal δ15N in late Pleistocene and early Holocene Europe

PLOS ONE RESEARCH ARTICLE Nitrogen palaeo-isoscapes: Changing spatial gradients of faunal δ15N in late Pleistocene and early Holocene Europe Hazel Reade ID1*, Jennifer A. Tripp1¤a, Delphine Frémondeau1, Kerry L. Sayle ID2, Thomas F. G. Higham3¤b¤c, Martin Street4, Rhiannon E. Stevens1 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 UCL Institute of Archaeology, University College London, London, United Kingdom, 2 Scottish Universities Environmental Research Centre, Glasgow, United Kingdom, 3 Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford, United Kingdom, 4 Römisch-Germanisches Zentralmuseum, Forschungsinstitut für Archäologie Kompetenzbereich Pleistozäne und Frühholozäne Archäologie, Neuwied, Germany ¤a Current address: Department of Chemistry, University of San Francisco, San Francisco, California, United States of America. ¤b Current address: Department of Evolutionary Anthropology, Faculty of Life Sciences, University of Vienna, Vienna, Austria. ¤c Current address: Human Evolution and Archaeological Sciences (HEAS), University of Vienna, Vienna, Austria. * OPEN ACCESS Citation: Reade H, Tripp JA, Frémondeau D, Sayle KL, Higham TFG, Street M, et al. (2023) Nitrogen palaeo-isoscapes: Changing spatial gradients of faunal δ15N in late Pleistocene and early Holocene Europe. PLoS ONE 18(2): e0268607. https://doi. org/10.1371/journal.pone.0268607 Editor: Luca Bondioli, University of Padova: Universita degli Studi di Padova, ITALY Received: May 3, 2022 Accepted: January 22, 2023 Published: February 6, 2023 Copyright: © 2023 Reade et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting information files. Data will also be available on the open access IsoArch repository after acceptance: https:// isoarch.eu/. Funding: This research was funded by an European Research Council (https://erc.europa.eu/) Consolidator Grant awarded to RS (Grant No. 617777). The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Abstract Nitrogen isotope ratio analysis (δ15N) of animal tissue is widely used in archaeology and palaeoecology to investigate diet and ecological niche. Data interpretations require an understanding of nitrogen isotope compositions at the base of the food web (baseline δ15N). Significant variation in animal δ15N has been recognised at various spatiotemporal scales and related to changes both in baseline δ15N, linked to environmental and climatic influence on the terrestrial nitrogen cycle, and animal ecology. Isoscapes (models of isotope spatial variation) have proved a useful tool for investigating spatial variability in biogeochemical cycles in present-day marine and terrestrial ecosystems, but so far, their application to palaeo-data has been more limited. Here, we present time-sliced nitrogen isoscapes for late Pleistocene and early Holocene Europe (c. 50,000 to 10,000 years BP) using herbivore collagen δ15N data. This period covers the Last Glacial-Interglacial Transition, during which significant variation in the terrestrial nitrogen cycle occurred. We use generalized linear mixed modelling approaches for interpolation and test models which both include and exclude climate covariate data. Our results show clear changes in spatial gradients of δ15N through time. Prediction of the lowest faunal δ15N values in northern latitudes after, rather than during, the Last Glacial Maximum is consistent with the Late Glacial Nitrogen Excursion (LGNE). We find that including climatic covariate data does not significantly improve model performance. These findings have implications for investigating the drivers of the LGNE, which has been linked to increased landscape moisture and permafrost thaw, and for understanding changing isotopic baselines, which are fundamental for studies investigating diets, niche partitioning, and migration of higher trophic level animals. PLOS ONE | https://doi.org/10.1371/journal.pone.0268607 February 6, 2023 1 / 21 PLOS ONE Competing interests: The authors have declared that no competing interests exist. Faunal nitrogen palaeo-isoscapes 1. Introduction Nitrogen isotope ratio analysis (expressed as δ15N) of biological tissue is frequently used in archaeology and palaeoecology to investigate dietary behaviours, ecological niche, and past food webs [1–3]. Specifically, δ15N is used to infer information about trophic structures. Obtaining reliable estimations of faunal trophic position requires understanding of the isotope compositions at the base of the food web. In other words, knowledge of the plant and soil δ15N values upon which the fauna lived and fed (hereafter termed baseline δ15N). However, this information is not usually readily obtainable from archaeological or palaeontological contexts, where the preservation of plant and/or soil material suitable for analysis can be limited. Moreover, plant and soil δ15N is highly heterogeneous and is not static in space or time, complicating inferences of baseline δ15N available to fauna. Many interconnected factors exert influence on plant and soil δ15N and nitrogen cycling in the terrestrial environment [4]. These relate to climate, plant functional type, mycorrhizal associations, soil characteristics, and the availability of different forms of nitrogen [5–8]. On global and continental scales strong, albeit indirect, relationships exist between plant δ15N and temperature and precipitation [6, 7]. These relationships are also expressed over smaller spatial scales with strong altitudinal gradients [9, 10]. Likewise, such spatial relationships are also represented in faunal δ15N values [9, 11, 12]. However, differences in dietary and mobility behaviours between different species, populations, and individuals introduce additional variations into the faunal δ15N signal [1, 3]. Indeed, while δ15N analysis of biological tissues is frequently used in archaeology and palaeoecology to investigate dietary behaviours and ecological niche, our ability to decipher environmental influence from feeding behaviour remains an ongoing challenge. On long timescales (103 to 105 years) significant temporal variation has been identified in herbivore δ15N [13–25]. This variation has been interpreted as representing changes to baseline δ15N in response to climatic and environmental drivers. Most notably, a large decrease and then rapid increase in herbivore δ15N occurred during the Late Glacial, between approximately 17,000- and 12,000-years before present (BP) [15–17, 20–23, 25, 26]. This trend occurs in multiple species, across a wide range of mid and high latitude environments and in recent years has been termed the (...truncated)