Expanding dietary and ecological insights of archaeofauna at Aqaba Castle, Jordan, using non-exchangeable hydrogen isotope ratio (δ²H) analysis

Non-exchangeable hydrogen isotope ratios (δ²H) are an underused proxy for studying past human-animal relationships, offering insights into diets, water intake, and ecological ranges. This study examines 218 bone collagen samples for δ¹³C, δ¹⁵N, and δ²H values of wild and domestic terrestrial species, and marine fishes from Ottoman-period Aqaba Castle, Jordan (16th–19th century CE). In this hyperarid region, high δ¹⁵N values reflect the elevated δ¹⁵N baseline of plants, causing overlaps in taxa with varying trophic levels. δ²H helps mitigate this by acting as an additional trophic level indicator. Domesticated herbivores mostly possess δ²H values close to that of predicted local rainfall, while hypercarnivorous cats (Felis catus) exhibit the highest δ²H values, averaging +42.4‰ above herbivores. Fish also show high δ²H values, correlated with trophic level (r = 0.84, R² = 0.70) and estimated body size (r = 0.61, R² = 0.37). Cattle and chickens, have the lowest δ²H values of all terrestrial species, likely due to their significant water requirements and the consumption of ²H-depleted aquifer water. Mapping wild gazelle (Gazella sp.) and chukar (Alectoris chukar) δ²H values on rainwater δ²H isoscapes indicates limited home ranges in the surrounding hyperarid highlands, in line with their expected behaviours. We assess the utility of δ2H for determining fish consumption using Bayesian dietary models for cats and hyenas (Hyaena hyaena), revealing higher fish consumption by cats when δ²H is included alongside δ¹³C and δ¹⁵N. This study highlights the value for δ²H values to enhance interpretations of animal diets and behaviours in archaeological contexts.

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