Pleistocene seasonal temperature variations recorded in the δ18O of Bison priscus teeth

Oxygen isotope analysis of phosphate in tooth enamel of mammals (δ18Op) constitutes a valuable method to reconstruct past air temperatures in continental environments. The method is based on interdependent relationships between the δ18O of apatite phosphate, body fluids, environmental waters and air temperatures. Continuous tooth growth and absence of enamel remodelling in bovid teeth ensures a reliable record of the intra-annual variability of air temperature through an incremental δ18O analysis from apex to cervix. This method has been applied to Bison priscus dental remains of the late Middle Pleistocene from the fossiliferous layer of a cave at Coudoulous I in South-Western France (Layer 4). The stacked oxygen isotope signal obtained by combining 9 bison teeth shows sinusoidal variations (15.0‰ to 19.1‰ V-SMOW) of seasonal origin over 2.5 yr. The corresponding computed MAT of 9 ± 3 °C is about 4 °C lower than at present. Seasons appear more contrasted in Coudoulous I during Layer 4 deposition with summers as warm as present ones (19 ± 3 °C) and significantly colder winters about 0 ± 3 °C compared to 6 ± 1 °C at present.