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This paper reviews the published literature regarding the climatic and hydrological variations of the past 8000 years in the northern Xinjiang of China in hope that some of the controversies surrounding the Holocene climate history can be reconciled. Based on the well-tested premise that the overall relationship between the A/C ratios and the bioclimates in arid and semi-arid areas of China still holds, we compared the A/C ratio-based SMI (Standardized Moisture Index) of five selected lacustrine sequences. Our comparison shows that the regional average SMI had a general rising trend, and the rising trend was reasonably corroborated by other pollen proxies. The rising trend can be explained by invoking its climatic linkage with the North Atlantic Ocean, and a possible linkage with ENSO is an additional or an alternative mechanism for explaining the rising trend. The nearly parallel rising trends of seven δ 18 O-indicated SSI curves (Standardized Salinity Index) mean that the lake-water salinity has been rising since ∼8.0 cal. ka BP. The rising trend can be explained by invoking the Holocene variations in the areal extent of ice covers in the Tianshan Mountains and the Altay Mountains. That is, the persistent shrinking of the ice extent in the mountains generated less and less melting water supplies to the lakes and thus resulted in saltier and saltier waters in the lakes. The contradiction between the increasing trend of the basin-wide moisture and the increasing trend of the lake-water salinity can be reconciled as follows: the increasing trend of the precipitation accompanied by the lowering tend of the temperature might have increasingly enhanced the effective soil moisture in northern Xinjiang, but the increase in the basin-wide moisture was not enough to compensate for the decrease in the lake inflowing water resulted from the shrinkage of ice-covered areas in the mountains. [ABSTRACT FROM AUTHOR]

This paper presents a new fossil pollen record from Tso Moriri (32°54′N, 78°19′E, 4512 m a.s.l.) and seeks to reconstruct changes in mean annual precipitation (MAP) during the last 12,000 years. This high-alpine lake occupies an area of 140 km 2 in a glacial-tectonic valley in the northwestern Himalaya. The region has a cold climate, with a MAP <300 mm, and open vegetation. The hydrology is controlled by the Indian Summer Monsoon (ISM), but winter westerly-associated precipitation also affects the regional water balance. Results indicate that precipitation levels varied significantly during the Holocene. After a rapid increase in MAP, a phase of maximum humidity was reached between ca. 11 and 9.6 cal ka BP, followed by a gradual decline in MAP. This trend parallels the reduction in the Northern Hemisphere summer insolation. Comparison of different palaeoclimate proxy records reveal evidence for a stronger Holocene decrease in precipitation in the northern versus the southern parts of the ISM domain. The long-term trend of ISM weakening is overlaid with several short periods of greater dryness, which are broadly synchronous with the North Atlantic cold spells, suggesting reduced amounts of westerly-associated winter precipitation. Compared to the mid and late Holocene, it appears that westerlies had a greater influence on the western parts of the ISM domain during the early Holocene. During this period, the westerly-associated summer precipitation belt was positioned at Mediterranean latitudes and amplified the ISM-derived precipitation. The Tso Moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient Harappan Civilisation, which flourished in the greater Indus Valley from approximately 5.2 to 3 cal ka BP. The prolonged Holocene trend towards aridity, punctuated by an interval of increased dryness (between ca. 4.5 and 4.3 cal ka BP), may have pushed the Mature Harappan urban settlements (between ca. 4.5 and 3.9 cal ka BP) to develop more efficient agricultural practices to deal with the increasingly acute water shortages. The amplified aridity associated with North Atlantic cooling between ca. 4 and 3.6 and around 3.2 cal ka BP further hindered local agriculture, possibly causing the deurbanisation that occurred from ca. 3.9 cal ka BP and eventual collapse of the Harappan Civilisation between ca. 3.5 and 3 cal ka BP. [ABSTRACT FROM AUTHOR]