Eemian climate seasonality reconstructed from intra-tooth oxygen, carbon, and nitrogen stable isotopes in equid enamel from Neumark-Nord 2, Germany

Reconstructing the climate of central Europe during the Eemian serves a dual purpose. First, the Eemian represents the most recent pre-Holocene period of widespread climate warming, and its vegetation structure offers a potential natural baseline for temperate European vegetation, as it was unaffected by large-scale anthropogenic alterations. Second, because Neanderthals lived in Europe during this period, understanding the climate provides insights into their environmental adaptations. Here we examined seasonal climate variation at a sub-annual scale during the early Eemian (ca. 121 ± 5 ka) by analyzing oxygen isotopes (δ¹⁸OCO3) in tooth enamel of 14 serially sampled equid third molars from the Neanderthal occupation site of Neumark-Nord 2 (NN2), Germany. These specimens were retrieved from find level NN2/2B, which spans less than 500 years. Stable carbon (δ¹³CCO3) and mineral-bound nitrogen isotopes (δ¹⁵Nmb) were measured in the same enamel aliquots to assess seasonal influences on diet. Intra-tooth δ¹⁸OCO3 values show clear sinusoidal seasonal patterns, indicating mean annual temperatures of 11 ± 1 °C, which are closely aligned with previously published Eemian estimates and slightly higher than present-day values. However, modeled water δ¹⁸O suggest stronger seasonal contrasts than today, with summers ∼5 °C warmer and similar winter conditions. δ¹³CCO3 values indicate a semi-open habitat and more annual precipitation than today. Notably, δ¹³CCO3 and δ¹⁵Nmb values show no seasonal variation, implying stable year-round equid diets and consistent plant availability despite pronounced climate seasonality.