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Origin and Migration of the Alpine Iceman

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Science  31 Oct 2003:
Vol. 302, Issue 5646, pp. 862-866
DOI: 10.1126/science.1089837

Abstract

The Alpine Iceman provides a unique window into the Neolithic-Copper Age of Europe. We compared the radiogenic (strontium and lead) and stable (oxygen and carbon) isotope composition of the Iceman's teeth and bones, as well as 40Ar/39Ar mica ages from his intestine, to local geology and hydrology, and we inferred his habitat and range from childhood to adult life. The Iceman's origin can be restricted to a few valleys within ∼60 kilometers south(east) of the discovery site. His migration during adulthood is indicated by contrasting isotopic compositions of enamel, bones, and intestinal content. This demonstrates that the Alpine valleys of central Europe were permanently inhabited during the terminal Neolithic.

A well-preserved human mummy, the “Iceman,” was recovered from a glacier located at the main Alpine watershed between Italy and Austria in 1991. The Iceman was ∼46 years old and lived ∼5200 years ago. Both the mummy and its associated equipment provided unprecedented insights into daily life during the late Neolithic-Copper Age of central Europe (14). One of the remaining questions regarding the Iceman is his place of origin. Molecular genetic analyses suggest that the Iceman's mitochondrial DNA closely resembles that of central and northern Europeans, including people from the Alpine region (5). Poor preservation prevented the recovery of nuclear DNA, thereby restricting better spatial resolution of his origin (5, 6). For the Iceman's late adulthood, his southern origin in presentday northern Italy has been deduced from the pollen and moss contents of his intestine (7, 8). The lack of pottery among his equipment prevented a conclusive archaeological analysis regarding his affinity to northern or southern cultures (2, 9), although a southern origin has been favored (3, 10).

We completed a comprehensive radiogenic (Sr and Pb) and stable (O and C) isotope study of samples of the Iceman representing different ontogenetic stages to determine his birthplace, habitat, and range (11). These samples include tooth enamel, dentine, cortical and trabecular bone, intestinal content, and his clothing and equipment. Enamel and bone represent archives of childhood and adulthood, respectively (12), whereas his activities during his last days can be inferred from the intestinal content. Isotopic tracing is based on the transfer (via nutrition) of the isotopic signatures of soils and waters into biominerals (13). Radiogenic isotopes allow provenance determination relative to the local geological environment, because different lithologies show systematic isotopic variations caused by the decay of long-lived radionuclides. Within the Iceman's potential habitat, at least four lithological units can be distinguished isotopically, including Mesozoic limestones, Permian volcanics (rhyolite), Eocene basalts, and a heterogeneous group of phyllites and polymetamorphic gneisses (Fig. 1). Stable isotopes provide information about altitude, latitude, or position relative to a watershed (oxygen) or paleodiet (carbon) (14, 15). The oxygen isotopic composition (δ18O) of precipitation can be reconstructed from δ18O in human biogenic apatite after correction for metabolically induced isotopic fractionation (16), because oxygen in biominerals is predominately derived from ingested water. Spatial variations in δ18O of precipitation arise from the preferential rainout of H218O from air masses during overland transport, making precipitation at higher altitudes or further inland systematically depleted in 18O. This is crucial for constraining the Iceman's origin, because he was found at an Alpine watershed, where there is considerable altitude contrast (Fig. 1). Areas north of the watershed predominately capture precipitation from the cooler Atlantic Ocean with long transport distances, whereas the nearby warmer Mediterranean Sea supplies water masses to the south. As a result, δ18O values of precipitation in the north are expected to be lower than those south of the watershed (17, 18).

Fig. 1.

Simplified geological-lithological map of the study area, showing the main lithologies that can be distinguished using radiogenic isotopes (supporting online text). The decrease in white mica ages (ages are shown in boxes) in polymetamorphic gneisses from northwest to southeast reflects the increasing overprint of an older (Variscan: ∼330 Ma) by a younger (Alpine: ∼90 Ma) metamorphic event (26). Values in parentheses indicate altitude in meters. The Alpine watershed runs alongthe border between Austria and Italy. Abbreviations are as follows. Archaeological sites: BA, Barbian; FE, Feldthurns; IS, Isera; JU, Juval; KA, Katharinaberg; MT, Margreid-Tolerait; PK, Pigloner Kopf; VP, Villanders/Plunacker; VS, Völs. Present-day towns: Br, Bruneck/Brunico; Bx, Brixen/Bressanone; Bz, Bozen/Bolzano; In, Innsbruck; La, Landeck; Me, Meran/Merano; Rv, Rovereto; Tn, Trento.

This is confirmed by the oxygen isotopic ratios presented here, which for rivers north of the Alpine watershed (in Austria) are ∼1 to 2 per mil (‰) lower than for southern rivers (in Italy) at similar longitude [for example, the Ötz versus the Schnals valley (Figs. 1 and 2A and table S1 (11)]. Areas near low-altitude passes such as the southern Wipp and Langtaufers valleys are influenced by both moisture sources because there is a limited amount of transfer across the watershed. Superimposed on the north-to-south variation is an overall lowering of riverine δ18O toward the west of the study area. Contributions of precipitation from the highest altitudes (that is, snow melt) make river water more negative in δ18O than small streams and springs, which at inhabited terraces above forested valleys are the likelier source of drinking water (Fig. 2A). Overall, the least-depleted δ18O values are found in the southeast of the area, in the Eisack/Isarco, Rienz, Hohlen, and Non valleys. Converting (16) the δ18O values of the Iceman's enamel to equivalent water values, it is inferred that he was drinking water with δ18O values between –10.6‰ (first premolar) and –11.0‰ (canine) when he was 3 to 5 years of age (table S1). These values are important because only waters south of the Alpine watershed have such high values (Fig. 2A). Cortical and trabecular bone samples indicate that during adulthood, the Iceman was drinking water with δ18O values of –11.7 and –11.4‰, respectively. These δ18O bone values are considered reliable because ice from the Iceman site yielded lower δ18O values (–13.4 to –16.4; the range may reflect varying contributions of northern and southern moisture sources). Postmortem alteration by meltwater would shift trabecular bone more toward lower δ18O values, yet the opposite is observed. Additionally, we converted δ18O data from present-day human enamel taken from third molars to equivalent water values (table S1) and found that they reproduced the observed δ18O values of corresponding streams and springs (Fig. 2A and supporting online text). Different valleys (such as the Eisack versus the Etsch/Adige) show resolvable clusters of δ18O teeth values, with the single outlier for each valley being explained by unaccounted-for migration. The interpretation of the Iceman's δ18O record assumes that relative differences in δ18O observed for present-day waters also existed ∼5200 years ago, which is corroborated by a speleothem from a cave located ∼110 km SE of the Iceman site. It records only minor fluctuations [∼0.3‰ δ18OPDB; as measured relative to the Pee Dee belemnite (PDB) standard] and similar δ18O values between 5350 to 5100 years ago and today (19).

Fig. 2.

(A) δ18O data [relative to standard mean ocean water (SMOW)] versus elevation for water and biomineral samples. Rivers are plotted as open symbols, local springs and streams appear as half-filled symbols, and modern tooth enamel samples (corrected for human-induced fractionation) appear as filled symbols. Green and red-purple colors denote rivers north and south of the Alpine watershed, respectively. Tooth and water data from the same valley appear in the same color. The δ18O values of water calculated from the Iceman's enamel and bones are indicated as shaded bars. Additional δ18O data from springs confirming that of the Etsch/Adige valley (ETs) are in (27). Abbreviations are as follows: EI, Eisack/Isarco; ET, Etsch/Adige; GB, Gröden; HO, Hohlen; IN, Inn; LT, Langtaufers; NO, Non; OT, Ötztal; RI, Rienz/Puster; RO, Rosanna; ST, Schnals; UT, Ulten; WI, Wipp; I, Iceman. The subscript “s” denotes local springs and streams located in the respective valleys. (B) 206Pb/204Pb versus 87Sr/86Sr isotopic data from tooth enamel and bones of the Iceman, plotted relative to data from soil leachates located on various lithologies (11). The error bars for soil leachates are smaller than the plot symbol. The arrow indicates the range of 87Sr/86Sr ratios obtained for canine enamel. See Fig. 1 for abbreviations. (C) Sr isotopic composition of various tissues versus the biological age of the Iceman. The contrasting Sr isotopic ratios of the various materials formed at different ontogenetic stages suggest the Iceman's migration during life (indicated by dashed lines). The inset shows a scanning electron photomicrograph of the smaller composite canine fragment. Data on the mineralization of enamel, dentine, and bones are from (15, 20), whereas the Iceman's biological age is from (4). Abbreviations are as follows: 3, canine; 4, first premolar; 5, second premolar; sm, small; lg, large; en, enamel; de, dentine; cort., cortical; trab., trabecular; int. cont., intestinal content.

Radiogenic isotope analysis was used to refine how far south the Iceman lived (table S2). Soil leachates (11) of the four main lithologies have distinct Pb-Sr isotopic compositions, although some overlap exists for the Permian volcanics and the gneiss/phyllite groups (Fig. 2B). These data are the basis for comparison with the radiogenic isotopic compositions of the Iceman's samples (11). Enamel fragments from all three teeth are characterized by uniformly high 87Sr/86Sr ratios of 0.7203 to 0.7206 for the main dissolution step (Fig. 2B and fig. S1). The smaller canine enamel fragment (3sm, Fig. 2C) records a higher Sr isotopic ratio of 0.7215, whereas for adjacent dentine, this value is only marginally higher than for the other three enamels. This allows the relative timing of all tooth fragments to be established, because enamel mineralizes a few months earlier than adjacent dentine (20), making the small canine piece the earliest formed tooth fragment. Its higher Sr isotopic signature may indicate a different diet during earliest childhood. Two cortical femur bone samples have lower 87Sr/86Sr ratios of 0.7175 and 0.7181, whereas for trabecular bone, this value is 0.7184 [final dissolution steps (Fig. 2B and fig. S1)]. In contrast to enamel, all bone leachates yield higher Sr isotopic ratios than the final dissolution. This is interpreted to reflect incipient postmortem alteration of bones due to interaction with high 87Sr/86Sr meltwater, which is consistent with ice cores closest to the Iceman that have high 87Sr/86Sr ratios of 0.723 to 0.729 (supporting online text). Immersion of the Iceman's body in water has also been deduced from the skin composition, trace elements in bones, and the distribution of artefacts (2123). Lower 87Sr/86Sr ratios for the enamel leachates do not record water-related alteration but are consistent with limited passive exchange of the outermost enamel with saliva having 87Sr/86Sr < 0.720 during adulthood, as deduced from the Iceman's bones. Dentine, having been shielded by enamel, has a uniform Sr isotopic composition. Enamel and bone Sr isotopic compositions of the final dissolution steps have to be regarded as close, but nevertheless minimum and maximum values for childhood and adulthood, respectively.

A comparison of Sr-Pb isotopic compositions of the Iceman's enamel with various soils reveals that regions dominated by limestones, basalts, and Permian volcanics can be excluded as being the Iceman's childhood area (Fig. 2B). These regions include the lower Etsch valley south of Bolzano and further south (Fig. 1). Instead, the enamel Sr-Pb isotopic signature is consistent with compositions of gneisses and phyllites, which occur near the Iceman site or in Schnals valley, Vintschgau [the Etsch/Adige valley (N)W of Merano], Ulten valley, middle Eisack valley, and lower Puster valley (Fig. 1). These interpretations based on Sr-Pb isotopes are consistent with δ18O data, because precipitation south of the lower Etsch/Adige valley (18) has higher δ18O values than inferred from the Iceman's biominerals. Similarly, regions far north of the Iceman site (north of Inn valley) that may record δ18O signatures of precipitation (17) compatible with the Iceman can be excluded on the basis of the prevalence of limestones (Fig. 1). The Sr-Pb isotopic composition of the Iceman's bones apparently matches those of Permian volcanics; however, it is known that other gneiss/phyllite areas are characterized by lower Sr isotope values, which overlap with the Permian volcanics (24, 25).

A sample of the Iceman's intestinal content was screened for cereal fragments (8) in order to constrain the origin of his last meal. Because not enough fragments were present, the entire sample was analyzed for its Sr isotopic composition, which is intermediate between the enamel and cortical bone compositions and continues the trend already indicated by trabecular bone (Fig. 2C). This intestinal sample also contained 12 100- to 400-μm white micas that are believed to have been ingested as a result of the grinding of cereal or from drinking water (supporting online text). These micas were individually analyzed for their 40Ar/39Ar ages (table S3), which is important because Permian volcanics, phyllites, and polymetamorphic gneisses exhibit different geological ages as a result of their different magmatic/metamorphic evolution during the Alpine [∼90 million years ago (Ma)] and Variscan (∼330 Ma) orogenies (26) (Fig. 1). The resultant white mica ages range between 95 and 300 Ma (with one at 440 Ma), with one broad peak between 160 and 220 Ma (seven micas) and a narrower peak between 285 and 300 Ma (three micas; fig. S2). This age distribution is found in the gneiss lithology only and excludes the Permian volcanics (276 Ma) and the phyllites (315 to 350 Ma). It demonstrates that the Iceman lived on gneissic soils during his later adulthood. Moreover, the variable but elevated Sr isotopic ratios of the Iceman's clothing and equipment (table S2) indicate that the Iceman used both animal and plant materials from a wider area located on gneiss/phyllite soils.

Our data indicate that the Iceman spent his entire life in the area south of the discovery site, which is consistent with palaeobotanical (7, 8) and most archaeological analyses (2, 3, 10) but extends earlier investigations into his childhood. This contrasts with a previous study (24) that concluded that the Iceman lived his final years in the Ötztal area north of the Alpine watershed. This was based on a comparison of trace elemental ratios and δ18O values between the Iceman's bones and soil-buried medieval bones (supporting online text).

Archaeological sites located on terraces in the Eisack valley record the closest match in δ18O values between the Iceman's enamel and modern human enamel (Figs. 1 and 2A). Furthermore, one site, Feldthurns, reveals the closest match in Sr-Pb isotopes between the Iceman's enamel and local soils (Fig. 2B). Excavations in Feldthurns have produced a menhir typical of the Copper Age of the region (3); thus, this may have been the region of the Iceman's childhood. Because areas with incompatible isotopic signatures can be excluded with greater certainty than positive assignments can be made, other potential childhood areas include the lower Puster valley (river Rienz), the lowest Vinschgau (Etsch valley) near Merano, and the Ulten valley. However, no archaeological sites from that period are known from the Ulten valley. Conversely, the different isotopic composition of the Iceman's bones argues for a different food source and hence migration to a region with distinct soil and water composition during his adulthood (Fig. 2C). This is also indicated by differences in δ13C between enamel and bone (table S1). More negative δ18O values in bone indicate migration to slightly higher altitudes or further to the northwest, where δ18O in precipitation is lower. Besides Sr-Pb-O isotopes, the white mica 40Ar/39Ar age distribution from his intestine, especially the 95-Ma age, is consistent only with a small area ∼10 to 20 km SW-NW of Merano in lower Vinschgau (the Etsch valley). Among others, this includes the site of Juval, which has been favored as the home of the Iceman during his adulthood (23). However, Juval has a Sr-Pb isotopic composition incompatible with that of the Iceman's bones (Fig. 2B).

An alternative scenario to that of permanent resettlement is seasonal migration, such as the Iceman's involvement in transhumance between low-altitude settlements in the south and summer grazing areas above the timberline in the north (such as southern Ötztal), which started in the Middle Neolithic and is still practiced today (23). If the δ18O value of ∼ –11‰ is taken to represent lower elevations, then the δ18O data of –11.7 and –11.4‰ for his cortical and trabecular bones are consistent with a decreasing residence during adult life (from ∼2 months to ∼1 month per year, respectively) in the southern elevated parts of Ötztal, with δ18O values of water of ∼ –15‰. An indication of the validity of this scenario may be the 87Sr/86Sr ratio of the Iceman's intestinal wall (table S2), which is similar to that of his earliest enamel and could represent the integrated value of his final few weeks or months during the late winter–early spring period.

Supporting Online Material

www.sciencemag.org/cgi/content/full/302/5646/862/DC1

Materials and Methods

SOM Text

Figs. S1 and S2

Tables S1 to S3

References

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