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

Abstract

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 14C 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 14C dating results demonstrates that ~62% of the Holocene samples were dated to 7–5cal kyr BP, and ~38% of the Holocene samples were dated to 4–2cal kyr BP, indicating an arid period during the early Holocene (before 8.0cal kyr BP), a humid period during the mid-Holocene (8.0–5.0cal kyr BP) and a humid to arid period during the late Holocene (after 5.0cal 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.