Untitled DocumentOrigin of the Neolithic Alpine Iceman: constraints from isotope geochemistry

Origin of the Neolithic Alpine Iceman: constraints from isotope geochemistry

W. Müller, H. Fricke1, A.N. Halliday2, M.T. McCulloch and Jo-Anne Wartho 3

1Department of Geology, Colorado College, Colorado Springs, CO 80903, U.S.A.
2Department of Earth Sciences, ETH Zürich, CH-8092 Zürich, Switzerland
3Department of Applied Geology, Curtin University of Technology, Perth, Australia

The discovery of a perfectly preserved late Neolithic human mummy in a glacier at the main Alpine ridge in northern Italy during autumn of 1991 was a truly unexpected finding. The 'Iceman' turned out to be ~5200 year old, and was found in-situ, i.e. outside an arranged burial site, together with his entire equipment. This finding thus provided the unique opportunity to investigate circumstances of 'real' life during the late Neolithic. One of the remaining open questions concerns the Iceman's origin, particularly regarding his early life. Did he grow up in the vicinity of the finding site or did he migrate to the area during his adulthood, i.e. was he a local or migrant? Because of the lack of pottery amongst the Iceman's equipment (substituted by more appropriate lightweight equipment such as birch-bark containers), his assignment to a contemporaneous culture either north or south of the Alps based on pottery typology was impossible. Here we utilize isotope geochemistry to answer the questions of origin and migration of the Iceman.

Combined radiogenic (Sr, Pb) and stable isotopic (O) analysis of a comprehensive suite of samples formed at different ontogenetic stages during the Iceman's life was conducted in order to unravel his origin and migration, both regarding his child- and adulthood. Investigated samples included enamel of three teeth, dentine, cortical and trabecular bone and intestine content. Soils from contemporaneous archaeological sites, river waters and modern human teeth were used for comparison. The oxygen isotope record of the Iceman's biominerals is consistent only with his southern origin, both valid for his childhood (enamel) and adulthood (bone). Areas north of the finding site (e.g. Ötztal) can be excluded. Based on Sr and Pb isotopes, the Iceman grew up on soils above gneisses and phyllites ('crystalline basement'), whereas carbonate or volcanic soils can be excluded (Fig. 1). This makes him a member of the local population from childhood onwards, as the former lithologies mainly occur close to the finding site. The isotopic compositions of bones suggest a different food source during his last ~10 - 20 years of life, and indicate the Iceman's migration during later life. This is currently investigated further, also using single grain 40Ar/39Ar ages of white micas recovered from the Iceman's intestine, as K/Ar and 40Ar/39Ar white mica ages vary considerably in the area under investigation, mainly as a result of strongly variable metamorphic overprint following the Alpine orogeny. The small difference in _18O between enamel and bone indicates that the Iceman did not spend protracted periods of his later life at elevated altitudes, for example in the southern Ötztal area, as in this case his bone oxygen should be isotopically significantly lighter.

Fig. 21: Diagram of Sr isotopic ratio vs. biological age of the Iceman. The different biominerals and the intestine content clearly record different Sr isotopic compositions for the various ontogenetic stages of the Iceman. The contrasting Sr isotope values for childhood and adulthood suggest migration of the Iceman during later life. e. ... enamel, d. ... dentine.