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).

采自天山（Tian Shan）东南端博斯腾湖的XBWu-46沉积岩芯孢粉数据（palynological data），反应该区域的湿度演化历史，可分为三个主要阶段：其一为干旱化阶段（约8540~4000校准距今年（cal. yr BP））；其二为最干旱阶段，时限约为4000~2000/1500校准距今年；其三为向岩芯顶部（约60校准距今年）湿度逐步升高的阶段。结合不同区域的其他气候代用指标记录进行对比分析可知，早全新世至中全新世期间中国西北地区的水文状况受控于亚洲夏季风（Asian summer monsoon）降水，而近两千年来的湿度升高则受西风带来源降水调控。湖相沉积记录的区域早期人类活动证据，始于最干旱阶段的起始时期，相关孢粉浓度升高的记录包括：炭化草屑浓度自约4350校准距今年起显著提升，谷类（Cerealia）型花粉始于约4000校准距今年，苍耳属（Xanthium）花粉始于约3700校准距今年，大麻属（Cannabis）型花粉始于约2500校准距今年。这些孢粉信号很可能与区域安德罗诺沃文化（Andronovo cultures）的早期农牧混合人群相关，据考古资料显示，该文化约于4000校准距今年出现在天山东南区域。此外，苍耳属花粉与炭化草屑浓度的升高，指示了汉朝（公元前206年-公元220年）丝绸之路（Silk Road）活动加剧所带来的人类活动影响增强。