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Calcareous root tubes or rhizoliths have a strong potential for paleoenvironmental studies, especially in reconstructing paleoenvironmental conditions and paleovegetation. Previous studies suggested that the effectivity of the moisture level affects the formation of calcareous root tubes in the deserts of the Alashan Plateau, Northwest China. However, it remains unclear whether the temporal distribution of calcareous root tubes can be used to reconstruct paleo-effective moisture in this area. In this study, based on conventional 14 C dating results of 34 Holocene calcareous root tube samples collected from the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in the Alashan Plateau of northwestern China, millennial-scale changes in paleo-effective moisture during the Holocene in this area were reconstructed. The frequency of the 14 C dating results demonstrates that ~ 62% of the Holocene samples were dated to 7–5 cal kyr BP, and ~ 38% of the Holocene samples were dated to 4–2 cal kyr BP, indicating an arid period during the early Holocene (before 8.0 cal kyr BP), a humid period during the mid-Holocene (8.0–5.0 cal kyr BP) and a humid to arid period during the late Holocene (after 5.0 cal kyr BP). The reconstruction results were consistent with other previous reconstruction results from lake sediments and aeolian sand–lacustrine sequences, which indicated that temporal distribution of calcareous root tubes can reflect millennial-scale changes in paleo-effective moisture in this area. However, a single sample could indicate local environmental changes that may differ from the overall desert environmental changes. Hence, the relatively humid environmental record obtained from the presence of calcareous root tubes is a local signal or a regional signal that should be noted. [ABSTRACT FROM AUTHOR]

Abstract: The Asian summer monsoon and the westerly winds interact in the mid-latitude regions of East Asia, so that climate change there is influenced by the combined effect of the two climate systems. The Holocene millennial-scale Asian summer monsoon change shows the out-of-phase relationship with the moisture evolution in arid Central Asia. Although much research has been devoted to the long-term climate change, little work has been done on the mechanism. Summer precipitation, in the marginal regions of the Asian monsoon, is strongly affected by the monsoon and the westerly winds. The purpose of this paper is to examine the mechanism of the millennial-scale out-of-phase relationship by modern summer precipitation analysis in the northwest margin of the Asian monsoon (95–110°E, 35–45°N). First, the method of Empirical Orthogonal Function (EOF) analysis was carried out to the 1960–2008 summer rainfall data from 64 stations in that region; then the water vapor transportation and geopotential height field data were studied, in order to explain and understand the factors that influence the summer precipitation; lastly, the East Asian Summer Monsoon Index (EASMI), South Asian Summer Monsoon Index (SASMI), Summer Westerly Winds Index (SWI) were compared with the EOF time series. The results indicate the complicated interannual-scale interaction between the Asian summer monsoon and the westerly winds, which can result in the modern out-of-phase relationship in the study area. This study demonstrates that the interaction between the two climate systems can be considered as a factor for the millennial-scale out-of-phase relationship. [Copyright &y& Elsevier]