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In arid regions, because of spatial variability, using single climate records is difficult to reconstruct the past climate change for the drainage basins. Holocene environmental records were collected from the upper, middle and lower regions of the Shiyang River drainage basin in the marginal area of the Asian monsoon (northwest China). The main objective of this paper was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin-wide environmental changes. During the early Holocene the vegetation was sparse, and the effective moisture was relatively low in the basin. The Holocene Climatic Optimum started between 7.0 and 8.0 cal ka BP, during which the lake level reached the highest level in the terminal lake; the vegetation density and the effective moisture reached the highest level during the Holocene in the drainage basin. From 4.7 cal ka BP the terminal lake began to shrink, while the vegetation density decreased dramatically. In the middle and upper regions of the drainage, the effective moisture began to decrease since 3.5 cal ka BP, and the arid tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin. During the early Holocene the relatively arid environment was affected by the gradually intensifying East Asian monsoon and the dry westerly winds. The mid-Holocene Optimum benefited from the intensive East Asian monsoon and the humid westerly winds. Then, the East Asian monsoon retreated since the late-Holocene. In the basin the arid tendency may be related to the retracting of the East Asian monsoon. However, the intensifying acidification after 1.5 cal ka BP may be correlated to the increasing dryness of the westerly winds. [ABSTRACT FROM AUTHOR]

In the Asian monsoon margin of northwest China, millennial-scale precipitation and effective moisture changes during the Holocene differ from those observed in the primary monsoon area. Whether these differences were caused by a change in precipitation or other hydroclimate factors remains controversial. We selected Huahai Lake, located in the western portion of the Hexi Corridor, at the northwest margin of the Asian monsoon area, to address this question. Using paleoclimate proxies (mineralogical assemblages and immobile elements) and results from a previous study, we inferred hydroclimate changes in this area during the early and middle Holocene (10.5-5.5 cal ka BP). Heavy precipitation and abundant runoff occurred during the early Holocene (10.5-8.8 cal ka BP). Proxies (carbonate content, total organic carbon and C/N) for precipitation minus evaporation (P − E) in the same section, however, revealed low P − E during the early Holocene and highest P − E in the middle Holocene (8.8-5.5 cal ka BP). Therefore, on a millennial timescale, precipitation amount and effective moisture changes were asynchronous during the early and middle Holocene. The precipitation and effective moisture pattern in the study area during that time span was different from patterns in both the Asian monsoon and westerly wind-influenced areas, suggesting an interplay between the two climate features. High precipitation during the early Holocene corresponded to a strengthened Asian monsoon. Highest P − E in the study area occurred during the middle Holocene and may have been caused by low evaporation, rather than high precipitation. [ABSTRACT FROM AUTHOR]