Chronological constraint of Neanderthal cultural and environmental changes in southwestern Europe: MIS 5-MIS 3 dating of the Axlor site (Biscay, Spain)

The cave site of Axlor (Biscay, Spain) preserves one of the most informative Middle Palaeolithic (MP) records for the North Atlantic Iberian region, though its age remains poorly known. Here we use single-grain optically stimulated luminescence (OSL) and single-grain thermally transferred OSL (TT-OSL) dating of sediments to improve the age constraint of Axlor's MP succession (levels N-B). Our new ages are consistent with the previously published terminus ante quem C-14 ages for the site (>42.9 cal ka bp), and suggest the sequence accumulated during a period of similar to 50 kyr. Axlor's levels N-F were deposited similar to 100-80 ka, probably during marine isotope stage (MIS) 5d-a, while levels D and B were deposited similar to 70 and similar to 50 ka, respectively, during MIS 4 and mid-MIS 3. Our results indicate that major faunal and technological turnovers occurred towards the end of MIS 5, potentially coinciding with broader environmental and climatic changes. Axlor's Quina record, dated here to the onset of MIS 4, is one of the oldest in Europe. Comparisons with neighbouring sites point to complex regional chronologies and development for this particular behaviour, though detailed correlations with other MP sequences remain difficult due to their poor chronological attributes. The present study highlights the important role that single-grain optical dating can play in elucidating the broader evolution of the MP across southwestern Europe.