Isotope fractionation

The sources and origin of tin, and the dispersion of bronze technology in the 3rd and 2nd millennium BC, are the central research topics of our multi-disciplinary research project, funded by an Advanced Grant of the European Research Council (ERC). It has the general goal to establish the tin isotopic composition of tin ores and tin-bearing artefacts, and considers the infl uence of anthropogenic processes on the isotope ratios. We discuss the tin isotopic composition of cassiterite from two major tin provinces in Europe: from Cornwall and Devon (Southern England), and from the Erzgebirge (Germany and Czech Republic). The samples from both tin provinces show a very large variation of isotopic compositions with δ124/120Sn-values ranging overall from -0.28 to 0.85‰. Although there is large overlap, on average, cassiterite from the Erzgebirge (δ124/120Sn = 0.09‰) is isotopically lighter than that of southwest England (δ124/120Sn = 0.18‰). This is due to a higher proportion of heavy isotope compositions in the samples from Cornwall and Devon. In addition, we compare the ore data with preliminary tin isotopic systematics in Early Bronze Age metal artefacts from the Únětice Culture in Central Germany and from several ancient settlements in Mesopotamia belonging to the Early Dynastic III and the Akkadian Periods. Bronze artefacts of the Únětice Culture containing more than 3 wt.% tin have rather constant isotopic compositions (δ124/120Sn = 0.2 to 0.31 ‰), despite having highly variable trace element concentrations and tin contents. This suggests the intentional addition of an isotopically homogeneous tin raw material (metal or cassiterite) to the copper ore or melt. In contrast, the tin isotopic composition of artefacts from Mesopotamia (>3 wt. % Sn) show a much larger δ124/120Sn variation from -0.2 to +0.4‰. This is even observed in single settlements such as Ur. Since there is no sizeable tin mineralization in the vicinity, this implies that the tin demand of the ancient metallurgist was covered by trading tin from different ore sources.

Abstract Prey-predator collagen enrichment values for carbon and nitrogen isotopic compositions are investigated. New enrichment values are given for the well-monitored ecosystem of Bialowieza primeval forest (Poland) for lynx and wolf. The impact of using different approximations in calculating such enrichment values is discussed.

Provenance studies of metal artefacts are well-established in the interdisciplinary field of science-based archaeology primarily using the chemical and isotopic composition. In the last decades, tin isotopes became gradually more important as a fingerprinting tool for the provenance of tin, but many questions especially regarding the behaviour of tin isotopes during pyrometallurgical processes are still not satisfactorily answered. This paper is a contribution to the understanding of tin isotope fractionation on tin ore smelting under prehistoric conditions and discusses the consequences for tin provenance studies. It presents the results of smelting experiments that were carried out with cassiterite in the laboratory and in the field, respectively. Besides chemical characterisation with XRF, SEM-EDX and Q-ICP-MS, tin isotope composition of tin ores and smelting products (tin metal, tin vapour, slag) were determined using solution MC-ICP-MS. Although tin recovery on smelting in the field was low (20-30%) due to tin losses to fuming and slag formation, the results indicate that the tin isotope composition is less affected than anticipated from theoretical considerations (Rayleigh fractionation). If cassiterite is completely reduced during the smelting reaction the tin metal becomes enriched in heavy tin isotopes with a fractionation of D124 Sn = 0.09-0.18‰ (0.02-0.05‰ u-1) relative to the original cassiterite. An estimate of the provenance of the original cassiterite and the potential ore source would still be possible because the variability of tin isotope ratios in tin ore provinces is much larger. If the cassiterite becomes incompletely reduced, however, then fractionation increases significantly up to D 124 Sn = 0.88‰ (0.22‰ u-1) and conclusions on tin sources are limited. Similarly, condensed tin vapours (D 124 Sn = 1.13‰ (0.28‰ u-1)) and slags (D 124 Sn = 0.42-1.32‰ (0.11-0.33‰ u-1)) that are by-products of the smelting process show large fractionation with respect to the original tin ore as well, which makes them unsuitable for provenance studies.

Within the past quarter century, researchers have taken steps to understand pathophysiological stable isotope fractionation within mammalian tissues more accurately. Biomedically, researchers have demonstrated that pulmonary disease, smoking, organ failure, anemia, anorexia, and changes in metabolic rate all affect the isotopic composition of human tissues and tissue by-products. This research strongly suggests that a relationship exists between human (patho)physiology and stable isotope biochemistry. Despite the results achieved by these studies, only a small minority of bioarchaeologists have attempted to elucidate these mechanisms in human skeletal and dental tissues. This research presents the results of a pilot study aimed at examining the degree to which bone collagen δ 13 C and δ 15 N values and enamel apatite δ 18 O and δ 13 C values vary between individuals with and without lesions indicative of a chronic anemia. Consistent with previous research, our results indicate that the enamel apatite of suspected anemics have significantly lower δ 18 O values relative to their lesion-free counterparts (U = 4.00, p = 0.05); however, this result was limited to the first permanent molar. Due to the small sample size and the lack of information concerning breast-feeding and weaning practices in the region during this time, it is not possible to link this variation definitively to the pathophysiology of anemia and/or its sequelae. There was no significant variation in bone collagen δ 13 C or δ 15 N values between anemic and lesion-free juveniles (δ 13 C: U = 26.00, p = 0.38; δ 15 N: U = 33.00, p = 0.85) or between anemic and lesion-free adults (δ 15 N: U = 2.70, p = 0.26; δ 13 C: U = 4.57, p = 0.10). A number of intrinsic and extrinsic factors may have contributed to the lack of variation. While sample sizes are small, the data indicate that future analysis is warranted. En el último cuarto de siglo, los investigadores han tomado medidas para comprender con mayor precisión Frac-cionamiento de isótopos estables fisiopatológicos en tejidos de mamíferos. Biomédicamente, los investigadores han Demostró que la enfermedad pulmonar, el tabaquismo, la insuficiencia orgánica, la anemia, la anorexia y los cambios metabólicos. La velocidad de todos los efectos de la composición isotópica de los tejidos humanos y los productos derivados del tejido. Esta investigación fuertemente sugiere que existe una relación entre la fisi-ología humana (patho) y la bioquímica de isótopos estables. A pesar de los resultados logrados por estos estu-dios, solo una pequeña minoría de bioarqueólogos ha intentado Elucidar estos mecanismos en los tejidos humanos esqueléticos y dentales. Esta investigación presenta los resultados de un estudio piloto destinado a examinar el