Significance and Limitations of Stable Oxygen Isotope Ratios in the Apatite Phosphate of Archaeological Vertebrate Finds for Provenance Analysis in an Alpine Reference Region

Abstract

Pb was established in the bioapatite of 219 individual archaeofaunal remains (cattle, pig, red deer) excavated from sites located along a specific transect of the European Alps, namely the Inn-Eisack-Adige-Brenner Passage, that has been of eminent importance since European prehistory. This reference area is vertically stratified, and since δ 18 O in the skeleton is influenced by climate, water source, physiology and even culture, we tested the relative contribution and importance of δ 18 O as a component of the *bs_bs_banner multi-isotope fingerprint for provenance analysis in this alpine region by a novel mathematical approach. In particular, we adapted a supervised learning approach through expectationmaximization (EM) clustering for fingerprint extraction and evaluated the contribution of each isotopic ratio to the data structure. While an altitude effect was evident in δ 18 O, its overall structural importance in the complete isotopic fingerprint was rather low. Therefore, provenance analysis of bioarchaeological finds in this region is possible by measuring stable Sr and Pb ratios alone, which is of considerable importance when δ 18 O values are not available, e.g., in cremated finds, although some information is lost. Whether this is tolerable depends on the scientific question to be solved.

Multi‐isotope provenancing of archaeological skeletons including cremations in a reference area of the European Alps

“…Such elevated ratios (>19) are frequent in the carbonate soils that dominate this region . In summary, both 87 Sr/ 86 Sr and 206 Pb/ 204 Pb in animal bones exhibit clear regional differences independent of species and should best characterize the three gross geographical areas along the alpine transect, namely the Northern Calcareous Alps, the Central Alps, and the Southern Alps …”

“…Despite the altitudinal variability of the Alpine transect, the stable oxygen isotopic ratios in the uncremated animal bones did not exhibit top structural relevance in the multi‐isotope animal data set after GMM clustering . At first glance, this came as a surprise because the altitude effect should lead to 18 O‐depleted ratios in the inneralpine regions, a fact that was clearly evidenced by the δ 18 O values in the uncremated animal bones . Comparison of the δ 18 O values between animal clusters ac0–ac3 revealed no significant differences (Kruskal‐Wallis, p 0 = 0.16).…”

“…The laboratory processing protocol for the measurement of 87 Sr/ 86 Sr in archaeological skeletons has been long established, and the isotopic variability per site well exceeds the isotopic variability of local individuals (±0.0003), with only a few exceptions . Moreover, it has been shown recently that the strontium isotopic signature of local water instead of soil leads to a far better predictability for the respective signature in the bones of large vertebrates.…”

“…19 This similarity analysis has proved successful previously with regard to stable isotopes of light elements 30 and proved superior to more common methods such as principal component analysis. 31 In this way, animal and human bones were grouped separately into clusters the members of which share the highest similarity in terms of the seven-(animals) to six-(humans) dimensional isotopic fingerprints. The results of the cluster analysis and the individual capture of samples into each cluster are published for the first time here.…”

Which isotopes should we choose? Entropy‐based feature ranking enables evaluation of the information content of stable isotopes in archaeofaunal material

“…A variety of methods are available for feature ranking. Recently, the Adjusted Rand Index (ARI) has been applied to multi‐isotope data to test the relative contribution and importance of δ 18 O phosphate values for provenance analysis . However, feature ranking can also be based on entropy.…”