Combining collagen extraction with mineral Zn isotope analyses from a single sample for robust palaeoecological investigations

Abstract

Collagen extraction from bones or dentine, commonly used for radiocarbon ( 14 C) dating and stable carbon and nitrogen isotope (δ 13 C and δ 15 N) analyses, involves the dissolution of the bioapatite of skeletal elements. This fraction is typically disposed of during pretreatment. Here, we test the possibility of utilising this dissolved mineral solution for analysis of the bioapatite zinc isotope composition (δ 66 Zn). Bioapatite δ 66 Zn is a novel trophic level indicator similar to collagen δ 15 N but with isotopic fractionation independent from nitrogen, thus providing additional dietary information. We tested ways to minimise Zn contamination of the dissolved mineral phase during collagen extraction. We then used archaeological bone samples from Ain Difla (Jordan) and Ranis (Germany) to compare δ 66 Zn values of dissolved bioapatite following our collagen extraction protocol with δ 66 Zn values from the same sample material dissolved in a metal-free cleanroom. Our results demonstrate that with only minor adjustments to minimise Zn contamination, the dissolved mineral solution from collagen extraction protocols commonly employed for 14 C dating and (palaeo)dietary analysis can be used for additional δ 66 Zn analyses even when collagen extraction does not take place in a cleanroom. Our protocol allows us to gain an additional dietary proxy to complement δ 15 N trophic level interpretations and perform more robust (palaeo)ecological investigations without further destructive sampling.

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