Indication of millennial-scale moisture changes by the temporal distribution of Holocene calcareous root tubes in the deserts of the Alashan Plateau, Northwest China

摘要

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 C-14 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 C-14 dating results demonstrates that similar to 62% of the Holocene samples were dated to 7-5 cal kyr BP, and similar to 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 lcyr 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. (C) 2015 Elsevier B.V. All rights reserved.