The Inca child of the Quehuar volcano: Stable isotopes clue to geographic origin and seasonal diet, with putative seaweed consumption

The Incas occupied the west coast of South America between 1438 and 1532 CE. Among the many rites they practised was the Capacocha, which involved the offering of children. Here we studied the mummy of a child found on the Quehuar volcano, Salta, Argentina. In order to determine the geographical origin of the child and to understand the living habits prior to its presentation as an offering, we incrementally measured the δ¹³C, δ¹⁵N, δ³⁴S and δ²H values of keratin from a hair strand and the δ¹⁸O value of apatite phosphate from a rib bone. Although the origin of the child remains uncertain, the oxygen isotope composition of the drinking water deduced from the rib composition argues for an origin between 2,500 and 3,000 m.a.s.l. bordering the Andes. Furthermore, the sinusoidal δ²H signal measured in hair is compatible with the recording of local seasonal precipitation variations. The results indicate that the child did not move or moved only briefly prior to death. This offering may have occurred at the onset of the wet season (summer), as suggested by the hair δ²H values. By combining δ¹³C, δ¹⁵N and δ³⁴S measurements in hair, we also proposed as the most parsimonious hypothesis that seaweed constituted a proportion (16.2 ± 12.9 %) of the diet, with a peak of consumption during the wet season (summer).