PROVENANCE STUDIES IN ARCHAEOLOGY BY 87SR/86SR ISOTOPE RATIOS IN MINERALIZED TISSUES – POTENTIAL AND PITFALLS USING THE EXAMPLE OF VIKING HAITHABU AND MEDIEVAL SCHLESWIG

Viking Haithabu and medieval Schleswig constitute a settlement continuum since the 9^th century. Both towns were important trading sites with contact to almost every part of the then known world. Based on the archaeological finds recovered from excavations, the development of this settlement continuum includes a change in economy and social structure and witnessed its change from an international trading locality to a prototypical medieval town complete with town charter. One outstanding aspect of the reconstruction of economic change is the quantification of immigrant people to the site, and the identification of imported animals and/or raw material of animal origin, to firmly distinguish migration and trade.

The desire to better understand past human and animal movement and patterning in history has benefitted substantially from developments in radiogenic isotopes research, especially the ⁸⁷Sr/⁸⁶Sr isotopic system as applied to bioarchaeological finds. Present maps, however, are generally inadequate for archaeological applications, primarily due to the isotopic composition of bioavailable strontium, which alone is capable of entering the biosphere and which can deviate significantly from the stationary, non-mobile strontium phase found in the soil. Therefore, adequate isotope maps must be established prior to any archaeological application. A variety of possibilities for the establishment of such maps has been suggested meanwhile, based on different samples such as archaeological finds of residential animals, mineral and surface water, or even archaeological human skeletal finds.

Both Haithabu and Schleswig are located on the North German plain, a region which has been shaped by the Weichsel glaciation and which exhibits a small scale stable Sr isotopic variability. In our study, we rely on the analysis of ⁸⁷Sr/⁸⁶Sr isotope ratios in bioarchaeological materials such as animal and human skeletal remains and preserved wood. We will show that the definition of “local” versus “non-local” specimens ultimately depends on the type of biomaterial analyzed and its respective strontium sources, how the analysis of a variety of materials will corroborate the definition of appropriate cut-off values, and how the contribution of dietary strontium limits the allocation to a consumer – be it human or animal – to a likely place of provenance.