Wet feet: developing sulfur isotope provenance methods to identify wetland inhabitants.

The stable isotopes of sulfur provide a distinctive signature for marine proximity and interaction. Exploring coastal proximity has been the principal application of sulfur isotopes in archaeology and palaeoecology, but this deals only with high (greater than 14‰) isotope values, meaning little interpretation has been gained from lower values. Progress has been hindered by issues with biosphere mapping. Air pollution can impact modern landscapes, significantly lowering sulfur isotope baselines, leading to the assumption that modern vegetation-based sulfur maps are not reliable. This research explores the potential of previously undiagnostic low, and often, negative sulfur isotope values for identifying wetland dwellers. Impervious clays that support wetlands are distinctive ecosystems and this study tests the hypothesis that they will produce low isotope values owing to both the underlying substrate and to redox conditions. Primary mapping of targeted areas using modern plants highlights zones with natural negative sulfur values and demonstrates that this constitutes a distinctive wetland signature. Analysis of modern and archaeological fauna demonstrates that these distinctive isotope compositions are transferred into the food chain. These findings propel the interpretative potential of sulfur isotopes forward and add to the growing knowledge to provide means for identifying archaeological humans and animals raised in wetlands.

A multi-isotope investigation of diet and subsistence amongst island and mainland populations from early medieval western Britain.

OBJECTIVES: This is the first investigation of dietary practices amongst multiple early medieval populations (AD 500-1000) from Wales and the Isle of Man using carbon, nitrogen, and sulphur isotope analysis. The analysis will illuminate similarities or differences between the diets and subsistence strategies of populations occupying different geographical regions, specifically those living in marginal coastal regions in comparison to inland populations well-connected to ecclesiastical centres and high-status settlements. MATERIALS AND METHODS: One hundred and two human skeletons were sampled for carbon and nitrogen isotope analysis, and 69 human skeletons were sampled for sulphur isotope analysis from nine cemetery sites from western Britain (Isle of Man = 3, southwest Wales = 4, southeast Wales = 2). Thirteen faunal skeletons from St Patrick's Chapel (southwest Wales) were sampled for carbon, nitrogen, and sulphur isotope analysis. RESULTS: Human δ13 C values range from -19.4‰ to -21.2‰ (δ13 C mean=-20.4 ±0.4‰, 1σ, n = 86), and δ15 N values range from 9.1‰ to 13.8‰ (δ15 N mean = 10.8 ± 0.9‰, 1σ, n = 86). δ34 S values range from 1.2‰ to 18.4‰ (δ34 S mean = 11.6 ± 4.5‰, 1σ, n = 66). Significant differences were noted between the mean δ13 C, δ15 N and δ34 S values according to geographic region: Isle of Man (δ13 C = -20.7 ± 0.4‰, δ15 N = 11.4 ±0.6‰, n = 13/86; δ34 S mean = 17.1 ±0.6, n = 4/66), southwest Wales (δ13 C = -20.5 ± 0.4‰, δ15 N = 11.0 ±1‰, n = 32/86; δ34 S = 16.1 ± 2.1, n = 21/66), and southeast Wales (δ13 C =-20.3 ±0.4‰, δ15 N = 10.4 ±0.7‰, n = 41/86; δ34 S= 8.8 ±3‰, n = 41/66). Faunal δ13 C values range from -23.1‰ to -21.2‰ (δ13 C mean= -22.1 ±0.5‰, 1σ, n = 13), and δ15 N values range from 6.3‰ to 9.8‰ (δ15 N mean = 7.3 ± 1.1‰, 1σ, n = 13). δ34 S values range from 4.7‰ to 18.4‰ (δ34 S mean= 16.3 ± 3.6‰, 1σ, n = 13). CONCLUSIONS: The data reveal a reliance on terrestrial protein, however differences are observed between the resource consumption of populations from southwest Wales and the Isle of Man in comparison to the populations from southeast Wales. Populations from the west coast have a marine sulphur signature that reflects their coastal proximity and may also include a reliance on seaweed as a fertiliser/food source. Populations in the southeast were connected to ecclesiastical centres and high-status settlements and had access to inland-grown produce. The data add support to the suggestion that δ34 S can be used as a mobility indicator.

The oxygen isotope relationship between the phosphate and structural carbonate fractions of human bioapatite.

RATIONALE: Oxygen isotope analysis of archaeological human dental enamel is widely used as a proxy for the drinking water composition (δ(18)O(DW)) of the individual and thus can be used as an indicator of their childhood place of origin. In this paper we demonstrate the robustness of structural carbonate oxygen isotope values (δ(18)O(C)) in bioapatite to preserve the life signal of human tooth enamel by comparing it with phosphate oxygen isotope values (δ(18)O(P)) derived from the same archaeological human tooth enamel samples. METHODS: δ(18)O(C) analysis was undertaken on 51 archaeological tooth enamel samples previously analysed for δ(18)O(P) values and strontium isotopes. δ(18)O(C) values were determined on a GV IsoPrime dual inlet mass spectrometer, following a series of methodological tests to assess: (1) The reaction time needed to ensure complete release of CO(2) from structural carbonate in the enamel; (2) The effect of an early pre-treatment with dilute acetic acid to remove diagenetic carbonate; (3) Analytical error; (4) Intra-tooth variation; and (5) Diagenetic alteration. RESULTS: This study establishes a direct relationship between δ(18)O(C) and δ(18)O(P) values from human tooth enamel (δ(18)O(P) = 1.0322 × Î´(18)O(C) - 9.6849). We have combined this equation with the drinking water equation of Daux et al. (J. Hum. Evol. 2008, 55, 1138) to allow direct calculation of δ(18)O(DW) values from human bioapatite δ(18)O(C) (δ(18)O(DW) = 1.590 × Î´(18)O(C) - 48.634). CONCLUSIONS: This is the first comprehensive study of the relationship between the ionic forms of oxygen (phosphate oxygen and structural carbonate) in archaeological human dental enamel. The new equation will allow direct comparison of data produced by the different methods and allow drinking water values to be calculated from structural carbonate data with confidence.

Multi-tissue analysis of oxygen isotopes in wild rhesus macaques (Macaca mulatta).

Oxygen isotopes in animal tissues are directly related to body water composition and thus the environment. Accurate measurement of animal tissue δ(18)O provides information about local climate, an animal's geographical origin and subsequent movements, with wide applications in palaeobiology and forensic science. The genesis and evolution of tissue-based oxygen isotopes within species and within individuals are complex. We present the first data, for non-human primates, rhesus macaques (Macaca mulatta), on the relationship between oxygen isotope sources in bio-apatite (PO(4) and PCO(3)) and hair taken from six sample sites in Asia, ranging from western India to northern Vietnam. The range of values is similar within each tissue type, with good correlation between tissues (r = 0.791 to 0.908), allowing cross-tissue extrapolations. This is important when the availability of suitable tissues is limited. Biological interpretation of the small data set is difficult: macaque diets are eclectic, and the samples are from various locations. However, factors such as overall climate, precipitation quantity and source, and altitude are clearly influencing the results for each discrete geographical grouping. Future work could be aimed at assessing δ(18)O tissue associations for other species as the relationships appear to be species-specific.