Carbon and Nitrogen Isotope Composition of Australasian Hair and Fingernails in a Global Context

The stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope composition of human bone and tissues encodes dietary information that in some circumstances can be attributed to geographical location. While there is a global dataset amounting to > 4000 samples, limited data are available for the Australasian region.

One hundred and seven nail/hair samples were detergent and solvent pretreated and analysed for δ¹³C and δ¹⁵N composition, sourced from individuals normally residing in southern Australia (temperate), northern Australia (seasonal tropical) and urban Papua New Guinea (tropical). Isotope values for nails were converted to hair keratin equivalent values using accepted fractionation factors. The results were compared with each other, and with the global datasets available from Europe, Asia, Africa and the Americas.

The southern Australian and Papua New Guinean data exhibit a similar mean and range to each other for both δ¹³C and δ¹⁵N values, comparable to results for some regions of Europe and Asia. The northern Australian data extends to higher δ¹³C values than the other groups due to a greater component of carbon in the diet ultimately from a C₄ source. Vegetarians exhibit a similar range to the omnivores in δ¹³C but tend to lower δ¹⁵N values.

Global supply chains and industrial fertilizer use have reduced the range δ¹³C and nitrogen δ¹⁵N values in the samples in this study, as has been the case globally. The range of values observed reflects the ability of consumers to access local produce from supermarkets or local markets. The Australasian data tend to lower δ¹³C values than the global average, indicating a dominance of carbon assimilated by C₃ photosynthesis in the diet. While similar to some European and Asian populations, δ¹³C values are lower than from regions with a high reliance on carbon assimilated by C₄ photosynthesis, including the Americas and parts of Africa.