Compound-specific radiocarbon dating of lipid residues in pottery vessels: a new approach for detecting the exploitation of marine resources

Over the last three decades, organic residue analysis has been shown to be especially useful in ancient diet reconstruction; however, it is only recently that the direct radiocarbon dating of lipid residues has become a reliable method for dating pottery vessels and food procurement activities. Here, we applied lipid residue analysis to 29 late Bronze Age pottery vessels from the site of Cliffs End Farm (UK), previously dated by their visible charred residues (carbonised food crusts) and dated four of these vessels by compound-specific radiocarbon analysis (CSRA) of their absorbed lipids. Lipid biomarker detection was limited to only one class of biomarker in four vessels, which indicated that the diet relied mainly on terrestrial animals. Four vessels datable from their absorbed lipids produced ¹⁴C measurements significantly older than the published results on the charred residues, suggesting a reservoir effect affecting the dated lipids. Furthermore, the low abundance of pig remains (1–4%) at the site suggests that enriched δ¹³C_16:0 and δ¹³C_18:0 values recorded on the absorbed fatty acids were caused by marine rather than porcine contributions. The percentage of marine products in the CSRA dated vessels was quantified using the δ¹³C values of individual fatty acids and values from a modern reference database. These percentages of marine products were incorporated in mixed-source radiocarbon calibration using OxCal for the correction of a marine reservoir effect (MRE). Therefore, the combination of lipid compositions, radiocarbon dates and faunal analyses enabled the identification of marine product exploitation at the site. Finally, this allowed the application of MRE corrections to the radiocarbon dates obtained, and comparisons to be made with those of charred residues obtained from the same sherds.