Stable isotopes of strontium (87Sr/86Sr), oxygen (δ18O), sulphur (δ34S) and lead (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) of tooth enamel served to establish the area of childhood residence and therefore the provenance of individuals from Schipluiden and Swifterbant. Stable isotopes of these elements are bound to the local underground geology, influenced by altitude, precipitation and distance from the sea, and as such specific for a geographical area (Budd et al. 2004). The research was carried out in cooperation with the University of Durham and published elsewhere (Smits et al. 2008). Samples were taken from human enamel and associated soils horizons, animals and /or grave pits to establish the local isotopic make-up and to rule out possible diagenetic influences (postdepositional absorbtion). The Swifterbant population appeared to be more homogeneous and of local origin, than the population at Schipluiden, which was more heterogeneous. Two non-locally grown individuals could be pointed out for Schipluiden and one for Swifterbant in a total sample population of 20 individuals on the basis of the combined strontium, lead and oxygen evidence (see figure 6 for the combined Sr and O values). The result of the sulphur isotope study discriminates roughly between the two groups but interpretation in view of distance from the sea is hindered by possibly diagenetic influences and failing information on the local S values. The two Schipluiden non-locals have no deviating Sr values, but show oxygen signals pointing to origins in eastern (continental) and south-western (Atlantic) directions. One of these individuals showed high Pb values and a more terrestrial diet as well, supporting the interpretation as non-local. The Swifterbant ‘immigrant’ has been primarily separated on the basis of the non-local Sr values, supported by high Pb values and a distinct terrestrial 13C/15N isotopic signature. One of the presumed ‘local’ people at Schipluiden had, however, similar 13C/15N values. In all of the five Schipluiden burials only ‘locals’ were interred, while both ‘immigrants’ were identified among the three investigated isolated remains. This may be seen as an indication that mortuary practices for non-local individuals were different from those of local people at Schipluiden. We have to be careful with such a conclusion in view of the low numbers of analysed samples and the non-straightforward interpretation of the complex isotope data patterns. Future research should be especially directed to this presumed relationship of origin and mortuary practice.
As the local interred individuals were men and children one wonders whether this group was patrilocal and if women migrated from other regions, but as the skeletal remains of women are almost undetectable in the isolated remains this hypothesis cannot be researched here.
Fig. 10 Combined Sr and O values for Schipluiden and Swifterbant (data derived from Smits et al. 2008). The dashed lines indicates the range of local oxygen values, the arrows indicate immigrants. Nos 1 and 2 are children, no. 3 is an individual from a different site and possibly a different date.