Bayesian estimates of marine radiocarbon reservoir effect in northern Iberia during the Early and Middle Holocene

Reconstructing the past variability of marine radiocarbon reservoir effects (MRE) is crucial for generating reliable chronologies for marine species and their consumers. We investigated the temporal MRE variability at the Early-to Mid-Holocene site of El Mazo (Asturias, northern Spain) by using a combination of new and previously published radiocarbon measurements on marine and terrestrial samples. The El Mazo site is characterized by overall well-defined archaeological layers of unknown occupation length with the predominant presence of two mollusc species (Patella vulgata Linnaeus, 1758 and topshell Phorcus lineatus [da Costa, 1778]) which were analysed for radiocarbon measurements. We employed the recently released IntCal20 calibration curve for the northern hemisphere and Bayesian modelling to reconstruct the site's chronology and temporal variability in MREs according to mollusc species. Obtained radiocarbon modelling results, although the estimate precision is not high, reveal a temporal variability in MREs that can be interpreted in view of known past climatic and environmental events such as the 8.2 ka event. The results also revealed differences in MREs according to mollusc species, which need to be taken into account in future chronological modelling. Overall, our results provide reference MRE values for the study of chronologies in northern Iberia during the Early-to Mid-Holocene. In this respect, a non-conservative Delta R reference for local marine samples dating earlier than c. 8.1 ka cal BP is -238 +/- 28 14C years.This research was performed as part of the projects HAR 2016-75605-R and HAR 2017-86262-P, funded by the Spanish Ministry of Economy and Competitiveness, MINECO. During the development of this research AGE was funded by the Basque Country Postdoctoral Programme through a postdoctoral grant (POS_2020_2_0032) and Uni-versity of La Rioja (no code available) . This study has also been sup-ported by the Prehistoric Research Consolidated Group of the Basque Country University (IT-1223-19) , funded by the Basque Country Gov-ernment. PR and RF are funded by the Max Planck Society. We thank the Fishing Activity Service of the Cantabrian Government for the authori-zation to collect modern specimens. We also thank the Max Plank So-ciety, University of La Rioja, Basque Country University (UPV/EHU) , University of Cantabria (UC) and Instituto Internacional de Inves-tigaciones Prehistoricas de Cantabria (IIIPC) for providing support