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The brief history of monitoring nutrient levels in Chinese lake waters limits our understanding of the causes and the long-term trends of their eutrophication and constrains effective lake management. We therefore synthesize nutrient data from lakes in China to reveal the historical changes and project their future trends to 2100 using models. Here we show that the average concentrations of nitrogen and phosphorus in lake sediments have increased by 267% and 202%, respectively since 1850. In the model projections, 2030–2100, the nitrogen concentrations in the studied lakes in China may decrease, for example, by 87% in the southern districts and by 19% in the northern districts. However, the phosphorus concentrations will continue to increase by an average of 25% in the Eastern Plain, Yunnan–Guizhou Plateau, and Xinjiang. Based on this differentiation, we suggest that nitrogen and phosphorus management in Chinese lakes should be carried out at the district level to help develop rational and sustainable environmental management strategies. Nutrient levels in Chinese lakes have rapidly increased since 1950 but future trends in lacustrine nitrogen and phosphorus across China will differentiate, according to projections up to 2100. [ABSTRACT FROM AUTHOR]

Arid central Asia (ACA) is dominated by mid-latitude westerlies and characterized by a climate optimum (a relatively humid climate that has supported the development of human culture) in clear contrast with the climate of monsoonal Asia during the Holocene. Significantly, whether the onset of the Holocene Climate Optimum (HCO) had an impact on cultural exchanges along the ancient Silk Road remains unknown. In this study, we compared the onset of the HCO in different parts of the vast ACA region by referring to a variety of previously established paleo-moisture/precipitation records. Intriguingly, we found significant differences in the onset of the HCO between the western and eastern parts of ACA. The onset of the HCO in the western part of ACA (i.e., to the west of the Tianshan Mountains) mainly occurred at ~8 ka BP (1 ka = 1000 cal yr BP). In contrast, the onset of the HCO occurred at ~6 ka in northern Xinjiang and even as late as ~5 ka in southern Xinjiang; this is a delay of 2–3 thousand years compared with the western part of ACA. These results likely indicate that the onset of the HCO occurred in a time-transgressive manner in ACA, namely, 'early in the west but late in the east'. On the other hand, we found that the onset of the HCO in the western part of ACA may have resulted in the inception of wheat planting and the development of agricultural civilization and that the onset of the HCO in northern Xinjiang may have prompted the southward migration of Afanasievo culture after ~5 ka. Additionally, the initiation of the HCO in southern Xinjiang could provide an environmental basis for the spread and planting of wheat and millet in this area after ~4.5 ka. We speculate that the spatial differences in the onset of the HCO in ACA are mainly related to temporal changes in the intensity and position of the mid-latitude westerly jet. Although the increase in insolation and reduction in the global ice volume would have led to an increase in the water vapor feeding the western part of ACA around 8 ka, the climate in the eastern part of ACA (namely, the Xinjiang region) could have only become humid after 6 ka when the westerlies were intensified and became positioned in the south. Moreover, the delayed HCO in southern Xinjiang probably benefited from the stronger westerly winds that appeared around 5 ka, which could have overcome the influence of the tall topography of the Tianshan Mountains. Therefore, in addition to external forcing (i.e., insolation), the ocean–atmospheric teleconnection, the regional topography, and their connection to the climate system are important in determining the spatial differences in the time-transgressive onset of the HCO in ACA. Our findings contribute to understanding the spatio-temporal characteristics of the hydroclimate in regions with complex eco-environmental systems and a diverse history of human activity. [ABSTRACT FROM AUTHOR]

Arid Central Asia (ACA) is far from oceanic moisture sources and has a prevailing arid climate; thus the environment of the region is hydroclimatically sensitive. The eastern part of ACA is dominated by the basin-mountain system. A previous study proposed that the humid mountains and the arid basins were characterized by an opposite pattern of climatic variation during the Holocene, with a long-term drying trend in the former and a wetting trend in the latter. However, robust evidence from an integrated basin-mountain system using the same geological archive is urgently needed to test this hypothesis. Here we present Holocene paleoclimatic results from two new loess sections, with reliable chronologies, from Tienshan Mountain slope. In combination with two additional loess records from the intermontane arid basin, a systematic mountain-basin comparison was carried out. The results indicate that a Holocene paleosol started to develop on the Tienshan Mountain slope (at an elevation of 1300–1600 m) during 7–5 ka, which is broadly synchronous with paleosol development in the arid basin (at an elevation of 500–800 m). Furthermore, magnetic-parameter-based precipitation reconstructions from the four loess sections all demonstrate a consistent wetting trend throughout the Holocene. Therefore, our findings do not support an anti-phased pattern of moisture/precipitation change between the humid mountains and the arid basins in eastern ACA. • The Holocene paleosols developed initially at 7–5 ka in the Ili Basin. • The humidity varies in-phase within the basin-mountain system in Central Asia. • The east of Ili Basin presented the larger humidity amplitude during the Holocene. [ABSTRACT FROM AUTHOR]

Although the pattern of Holocene temperature variations in central Asia is complex, it is clear that temperature played a fundamental role in influencing humidity conditions and regional human activity. We reconstructed temperature changes using Pediastrum species data, verified by clumped isotopes (Δ 47), in the carbonates of sediment cores recovered from Bosten Lake in Xinjiang Province, northwestern China. Combined with archaeological data, the results indicate an unusually warm climatic interval that peaked at ∼4.7–4.3 kyr and promoted human occupation of the Altai Mountains. The climate cooled during 4.2–4.1 kyr and 3.6–3.5 kyr, as indicated by the decrease or absence of Pediastrum simplex. These cold events may have triggered the southward human migration out of the Altai region, resulting in the widespread distribution of archaeological sites at lower latitudes, in the Tienshan Mountains, and in the desert-oasis areas of the Tarim Basin in southern Xinjiang. Our data support the notion that a series of cultural transitions across the monsoonal Loess Plateau and Tibetan Plateau of China may have been linked to temperature changes during the middle to late Holocene. • Reconstructed an unusually warm climate during 4.7–4.3 kyr based on Pediastrum assemblage records. • Clarified cold climate might have caused human southward migrations in central Asia. • Human migrations and temperature changes have caused major culture shifts in western China. [ABSTRACT FROM AUTHOR]