Absolute counts and concentrations of pollen and non-pollen palynomorphs from the sediment core XBWu-46 extracted from Bosten Lake (Bosten Hu) covering the last 8540 years and a clay sample from mud coffin BM28 from the Xiaohe cemetery in western China

The palynological data of the XBWu-46 sediment core extracted from Bosten Lake at the south-eastern end of the Tian Shan represents the regional moisture evolution, which can be divided into three major intervals comprising a period of aridification (ca. 8540-4000 cal. yr BP), a driest phase spanning from ca. 4000 to 2000/1500 cal. yr BP, followed by an interval of increasing moisture levels towards the core top (ca. 60 cal. yr BP). Correlation with other climate proxy records from different regions implies that hydrological conditions in NW China during the early and middle Holocene were governed by Asian summer monsoon precipitation and that the moisture increase over the last two millennia was controlled by westerly-derived precipitation. Evidence for early regional human activities in the lake sediments starts to accumulate from the onset of the driest interval including the records of enhanced charred grass fragment concentrations (since ca. 4350 cal. yr BP), Cerealia type (since ca. 4000 cal. yr BP), Xanthium (since ca. 3700 cal. yr BP), and Cannabis type (since ca. 2500 cal. yr BP) pollen. These signals are likely related to early agro-pastoral populations of regional Andronovo cultures that, according to archaeological data, appeared in the south-eastern Tian Shan around 4000 cal. yr BP. In addition, increased Xanthium pollen and charred grass fragment abundances point to enhanced human impact linked to intensified Silk Road activities during the Han dynasty (206 BCE-220 CE).