Formula omitted] as a dietary indicator in modern and archaeological bone

Abstract

Strontium isotope ratios ( 87Sr 86Sr ) in human and animal bone are inherited, via foodstuffs, from rocks in the areas in which an individual lived. If such an area includes more than one rock type with differing 87Sr 86Sr , or is coastal region with terrestrial 87Sr 86Sr different from that of the sea, then bone strontium isotope ratio measurements provide a measure of the relative importance of foods from each isotopic zone. In the southwestern Cape of South Africa, marine and coastal terrestrial areas (covered by marine sands) should yield foods with 87Sr 86Sr close to the marine average, while the Cambrian and pre-Cambrian shales and sandstones of the hinterland ought to be enriched in 87Sr (from radioactive decay of 87Rb during the considerable time elapsed since they were laid down). Analyses of modern animal bones show that these patterns do prevail, furnishing us with a new means of reconstructing prehistoric diets. Preliminary measurements on archaeological human material recovered from coastal shell-midden sites apparently reflect heavy reliance on coastal foods. However, these bones have been shown to be contaminated with diagenetic marine strontium from the shells in the middens. Experiments on faunal specimens show that diagenetic strontium can be removed by repeated washing in acetic acid/sodium acetate buffer. Mineral with 87Sr 86Sr similar to the burial environment dissolves first, while subsequent washes remove strontium with different 87Sr 86Sr . For two coastal human skeletons, however, the marine/coastal terrestrial nature of the isotopic signature remains. Further experimental work is required in order to establish the limits of the technique; however, a combination of the solubility profile method and strontium isotope analysis promises to provide a powerful tool for reconstructing palaeodiets.