The occurrence and diagnostic potential of aquatic biomarkers: Guidance for freshwater resource identification for archaeological pottery lipid residue analysis

The processing of aquatic (marine and freshwater) resources in archaeological pottery is identified through the detection of ω-(o-alkylphenyl)alkanoic acids (APAAs), dihydroxy fatty acids (DHYAs), and isoprenoid fatty acids in preserved lipid residues. Certain biomarkers are considered more diagnostic of aquatic resources, but published methodologies frequently use different combinations of biomarkers as evidence for freshwater resource processing. This study determines the most diagnostic biomarkers of freshwater resource processing in European prehistory. A literature survey comparing the fatty acid composition of relevant freshwater and terrestrial species, found that long chain (≥C20) mono- and polyunsaturated fatty acids occur in higher abundance in freshwater fish, but considerable inter- and intraspecies variation was observed. The occurrence of isoprenoid fatty acids was also investigated through the analysis of modern reference fats and lipids extracted from experimental cooking vessels, demonstrating that 4,8,12-trimethyltetradecanoic acid (TMTD) occurs in freshwater fish, ducks, and mussels, but is not exclusive to aquatic resources. Various combinations of aquatic biomarkers were detected in extracts of archaeological and experimental vessels used for freshwater resource processing, and the most diagnostic biomarkers (≥C20 APAAs/DHYAs) were not consistently detected. Findings are integrated into an interpretive framework for the analysis of archaeological lipid residues and the identification of freshwater resource processing. The results promote a standardised interpretive approach to freshwater resource identification and highlight the limitations of aquatic biomarkers.