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The Ancient Silk Road played a crucial role in cultural exchange and commercial trade between western and eastern Eurasia during the historical period. However, the exchanges were interrupted in the early 16th century AD, in the Ming dynasty. Three causes of the demise of the ancient Silk Road have been suggested: (1) the thriving of the sea trade route after the great geographic discovery in the Ming dynasty; (2) frequent incursions by the Wala and Turpan kingdoms, or fighting in border areas; and (3) climate change. In this study, new evidence from a sedimentary site in Dunhuang oasis together with analysis of historical archives indicate that neither the sea trade route nor the frontier wars were the pivotal reason for the closure of the Jiayuguan Pass. Extreme droughts and desertification events, caused by climate change, occurred in the Dunhuang area, west of the Jiayuguan Pass, during ~ 1440-1460 AD. After ~ 1450 AD, desertification rendered the ancient Silk Road impassable in the area, which resulted in a steep fall in the volume of trade as well as political chaos and mass migrations. The final closure of the Jiayuguan Pass in 1539 AD and the abandonment of Dunhuang city further interrupted the operation of the ancient Silk Road. [ABSTRACT FROM AUTHOR]

This study investigates the sediment fluxes through the Yellow River sediment routing system, which are among the largest in the world, by constructing a sediment budget of the system over the period from 1855 to 1968. The framework of the sediment budget includes four functional units with the upper and middle reaches of the river as the sediment source and its lower reaches, its delta, and the deep sea as the sediment sinks. Sediment yield from the source and amounts of deposition in the lower Yellow River and the modern Yellow River delta were estimated for completing the sediment budget. The sediment budget produced for the period from 1855 to 1968 was characterized by a sediment input of 1.837 × 1011 tonnes and a distribution of the sediment between the lower Yellow River, the delta, and the deep sea of 64%, 33%, and 3%, respectively. The details of the sediment budget show that the importance of sedimentation in the lower Yellow River changed greatly with variations in the condition of the dykes and other human activities. A comparison of the sediment budgets of the delta for different timescales shows that the proportion of sediment dispersed to the deep sea decreases as the timescale over which the sediment fluxes are investigated increases. [ABSTRACT FROM AUTHOR]

On the basis of concentrations of 21 major and minor elements in a well-dated sediment core from the deepwater part of Lake Erhai, principal component analysis (PCA) reveals three main factors controlling the inorganic chemical composition of lake sediments. These are physical erosion in the watershed (Component 1), autochthonous calcite precipitation in lake water (Component 2) and early diagenesis in sediments (Component 3). Variations of factor scores of Component 1 and Component 3 may reflect fluctuations in rainfall and temperature, respectively in the lake region. High factor scores of Component 3 correlate with low factor scores of Component 1 in sediments within the intervals AD 1340–1550 and AD 1890–1950, indicating two warm-dry episodes. Low factor scores of Component 3 correlate with high factor scores of Component 1 from AD 1550–1890, indicating a cold-wet climate corresponding to the 'Little Ice Age' in Europe. Our study provides a new approach to reconstructing palaeoclimate, and adds to a growing body of evidence for a widespread cooling during the 'Little Ice Age'. The alternation between warm-dry and cool-humid conditions possibly implies different climate change characteristics between the southwest monsoon zone and the southeast monsoon zone where the climate pattern is warm-humid and cool-dry. [ABSTRACT FROM AUTHOR]