Rethink the subsistence of Pastoralists in the Middle Tian Shan: carbon and nitrogen isotopes evidence for the mixed subsistence in Wulasitai Valley, Xinjiang, 900BC – 1500 AD

The Middle Tian Shan has often been characterised as a predominantly pastoral or nomadic zone during the Iron Age and historical periods, yet the role of agro-pastoral strategies in shaping subsistence practices in this mountainous region remains poorly understood. This study presents new carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope data from human bone collagen recovered from the Wulasitai Valley in the central Tian Shan, China, spanning the Early Iron Age to the late historical period (ca. 900 BC–AD 1500). The isotopic results indicate that subsistence in the Wulasitai Valley was consistently based on a mixed agro-pastoral economy, combining C₃ plant consumption with substantial intake of terrestrial animal protein, including meat and dairy products. While δ¹⁵N values remain relatively stable through time, suggesting long-term continuity in animal protein consumption, δ¹³C values fluctuate markedly, reflecting variable incorporation of C₄ plants, particularly millet. By integrating isotopic evidence with regional palaeoenvironmental data from the Bosten Lake basin and modern climatic proxies, this study demonstrates that climatic variability and environmental constraints played a critical role in shaping dietary strategies. These findings challenge simplified models of uniformly pastoral lifeways and highlight long-term subsistence flexibility and environmental adaptation within the Tian Shan Mountain Corridor.