Environmentally adjusted δ13C thresholds for accurate detection of C4 plant consumption in Europe

Abstract Detecting C 4 plants consumption is central to investigating animal ecology, agriculture, dietary transitions, and socio-environmental adaptations, and can be done using carbon isotope analysis. The conventional δ ¹³C threshold used to identify C 4 plant intake does not consider substantial ecological variability across Europe. By analyzing over 4,000 δ 13 C values from archaeological C 3 and C 4 grains, we present a European-wide C 3 grain δ 13 C baseline and establish adjusted δ 13 C threshold estimations for C 4 consumption from the site to the ecozone scale using multicomponent environmental models and ecozone cluster analysis. We show that a fixed threshold lead to under- or overestimation of C 4 plant consumption, particularly in northern/humid and southern/arid regions, where the threshold needs to be revised downwards or upwards by up to 2‰. This refined framework offers a more accurate baseline for interpreting human and animal diet and enhances our understanding of the spread, adoption and consumption of C 4 crops across Europe.