Resolution and limits of isotopic approaches to puzzle out seasonal herd mobility. A modern case study from Azerbaijan
Résumé
Herd mobility is a key parameter of many agro-pastoral strategies. Sequential variations
of oxygen, carbon and strontium isotope ratios in ruminant teeth are commonly used for
characterizing herd mobility along altitudinal gradients and across geological areas. To
what extent is the variation and covariation of isotopic ratios along a tooth actually
reflecting vertical and geological mobility? The interpretation of such data fom
archaeological material widely depends on our ability to answer to this question. Few
modern baselines are available to assess covariation of oxygen and carbon isotope ratios
along the tooth of modern sheep experiencing vertical mobilities. There are no such
baselines for the covariation of strontium, oxygen and carbon isotope ratios. Our study
aimed at analyzing the variation and covariation of isotope ratios of oxygen, carbon, and
strontium in the teeth and guard hair of domestic ruminants experiencing different
pastoral mobilities along altitudinal gradients and across geological areas. We sampled
lower molars from one cow and 17 sheep, as well as the guard hair from five goats, all
grazing in different mountainous areas of Azerbaijan (Nakhchivan, Ganja-Qazakh, and
Lankaran regions) at least part of the year. Our results suggest that the covariation of
the isotope ratios of oxygen and carbon allow to spot easily the specimens moving
seasonally between the plains and the highlands and also between the subalpine zone
and the highland meadows. To a lesser extent it is possible to sort two-staged annual
mobility from four-staged annual mobility. The variations in strontium isotope ratios
during the period of enamel formation also adequately reflect seasonal mobility but it
deeply depends on the number of samples analyzed along the tooth crown. These results
allow us to interpret isotope ratio variations in archaeological domestic ruminant teeth in
order to analyze the role of herd mobilities in past agro-pastoral communities.