Holocene Millennial‐Scale Precipitation Variations in the Asian Summer Monsoon Margin of Northwest China and Their Relation to Migrations of Monsoon Northern Boundary via Oxygen Isotope Analysis of Calcareous Root Tubes in Deserts

Abstract

AbstractThe Asian summer monsoon (ASM) margin of northwest China is a critical region for studying Asian monsoon variability during the Holocene. However, the pattern of precipitation variations and migration of the ASM northern boundary in arid regions during the Holocene remains unclear. In this study, we analyzed oxygen isotopes of 70 calcareous root tube (CRT) samples from the desert hinterlands in the ASM margin of northwest China, including the Badain Jaran, Tengger, Ulan Buh, and Kubuqi deserts. The CRT samples were analyzed to reconstruct millennial‐scale precipitation variation patterns during the Holocene and further explored the location of the ASM northwestern boundary during the middle Holocene. Our results demonstrated that the δ18O values of CRTs during the late Holocene (4.0–1.0 cal kyr BP) were all less negative than those during the middle Holocene (8.0–4.0 cal kyr BP), which revealed that the precipitation decreased from the middle Holocene to the late Holocene. Moreover, an increase in δ18O values from the southeast to northwest revealed that the precipitation decreased. We argued that the Holocene millennial‐scale precipitation changes in this region were influenced by the migrations in the ASM northern boundary. During the middle Holocene, due to the strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in increased precipitation. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation.