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

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.

Stable isotopes show Homo sapiens dispersed into cold steppes ~45,000 years ago at Ilsenhöhle in Ranis, Germany

“…Nitrogen isotope variability in arctic biomes shows the highest values in grasses and herbaceous plants over shrubs or trees and this transfers to high δ 15 N values in specialized grazers 31 . Glacial phases are often accompanied by low δ 15 N values in fauna due to limited nitrogen availability and reduced bacterial activity in cold-wet soils, while high δ 15 N values are observed in phases with higher temperatures or low moisture availability 32 , 33 . As δ 18 O values demonstrate low temperatures in this interval, high δ 15 N values could indicate dry soil conditions and/or strong grazing specialization of equids, which both imply the presence of an open steppe environment.…”

Use of historical isoscapes to develop an estuarine nutrient baseline

“…Further, oyster shell d 15 N data constrained the timing of increased sediment N loads associated with anthropogenic activity in the Chesapeake Bay Watershed (Black et al, 2017). Prior baseline studies often provide isotope timeline data with separation of locations over time, but isoscapes with high-spatial resolution are a recent application to historical and palaeo-contexts (Reade et al, 2023).…”

“…The term isoscape refers to any spatial representation of isotope data (West et al, 2008). Isoscapes are established in earth system research (Bowen, 2010) and emerging in paleoenvironmental studies (Reade et al, 2023). Their use has been applied to a variety of spatiotemporal questions to identify spatial patterns in N fixation (Hellmann et al, 2016), fossil fuel combustion (Bowen 2010), variability in river water sources (Brooks et al, 2012), as well as for tracking migratory animals (Hobson et al, 2009).…”

pastclim 1.2: an R package to easily access and use paleoclimatic reconstructions

“…The availability of such data paved the way for a large number of research questions among many disciplines, i.e. ecology (Miller et al 2021b, VanBuren and Jarzyna 2022), paleoecology (Leonardi et al 2018, 2022, Somveille et al 2020, Chen et al 2021, Schap et al 2021, Thorup et al 2021, Medina‐Castañeda et al 2022, Reade et al 2022), conservation (Beyer and Manica 2021), population genetics (Maisano Delser et al 2021, Miller et al 2021a, Warmuth et al 2021), archaeology (Betti et al 2020, Racimo et al 2020, Beyer et al 2021, Krzyzanska et al 2021, Bradshaw et al 2022, Cerasoni et al 2022, Park and Marwick 2022, Timbrell et al 2022), macroevolution of different taxa, including the genus Homo (Saupe et al 2014, Will et al 2021, Fordham et al 2022, Timmermann et al 2022, Troyer et al 2022), anthropology (Leonardi et al 2017, Padilla‐Iglesias et al 2022) and linguistics (Beyer et al 2019).…”