High-resolution palaeodietary reconstruction: Amino acid δ¹³C analysis of keratin from single hairs of mummified human individuals

Stable isotope analysis of mummified human hair allows the reconstruction of the recent life histories of individuals that died thousands of years ago. The objective of this study is to improve the resolution of hair palaeodietary reconstruction by sequentially analyzing 0.5 cm segments of a single hair using liquid chromatography-isotope ratio mass spectrometry (LC/IRMS). The subsistence strategies of seven individuals, spanning different cultures/periods (Chinchorro, Formative, Inca) and covering different geographic areas (coasts and hinterland) of the Atacama Desert, northern Chile, were reconstructed by analyzing δ¹³C amino acid compositions using an improved methodology that requires only 0.5 cm segments of a single hair. The amino acid δ¹³C values were supplemented with bulk carbon, nitrogen and sulfur isotope analysis performed on multiple hairs. Our results show that the archaic hunter-gatherers strongly relied on aquatic resources, as did the first transitional Formative individuals living on the coasts. Conversely, the Formative inhabitants of the nearby valley exhibit consumption of terrestrial resources in a seasonal pattern. A broader dietary spectrum made of mixed terrestrial and aquatic foods is identified in the Inca individual. The sequential analysis of 0.5 cm increments from a single hair has permitted the high-resolution reconstruction (approximately fortnightly) of the recent life history of these pre-Columbian individuals, discerning short-term nutritional changes related to agricultural cycle, multiple dietary intakes or mobility. Although bulk methods can detect changes in diet and track seasonal shifts, the variations in the carbon isotope signal can be highly attenuated with respect to the dietary intake because of the use of multiple hairs.