Search

Calcareous root tubes are widely distributed across the Badain Jaran Desert and the Tengger Desert of the Alashan Plateau in northwest China. However, the reliability of their 14 C dating results and their environmental significance remain unclear. In this study, the conventional 14 C ages of 31 calcareous root tube samples and one aquatic mollusc shell sample, which were all collected from the Badain Jaran Desert and the Tengger Desert, were measured. The results reveal that nine of the 14 calcareous root tube samples from the Badain Jaran Desert were from Marine Isotope Stage (MIS) 3, while two samples were from MIS 2. The other three samples were dated to the mid-Holocene, one of which is consistent with the aquatic mollusc shell sample collected from the shoreline of Zhunzhahanjilin Lake in the Badain Jaran Desert. Moreover, the 17 calcareous root tube samples from the Tengger Desert were all dated to the mid- and late-Holocene, most of which were from the mid-Holocene. The results demonstrate that calcareous root tubes can be used as 14 C dating materials and that the accuracy of their 14 C dating depends on the time scale. The dating results were reliable at the millennial scale. However, the reliability of the ages from MIS 3a is lower than that of the Holocene ages, though the ages were reliable in tens of thousands years. Based on the statistical analysis, the overwhelming majority of calcareous root tubes collected from the deserts of the Alashan Plateau were formed during MIS 3a and the mid-Holocene. The concentrated emergence of calcareous root tubes in phases implies that they were formed during periods of relatively humid environments in desert areas, arid regions. Moreover, the results indicate that the effectivity of the moisture level probably affects the formation of calcareous root tubes, and the presence of calcareous root tubes indicates the occurrence of periods of relatively humid environments in the study area. [ABSTRACT FROM AUTHOR]

Abstract: The pattern of Holocene environmental changes in the Asian monsoon margin on a millennial timescale remains controversial. Based on lithological characteristics and sedimentological proxies, we reconstructed Holocene-effective humidity changes and the lake evolution of Huahai Lake in the marginal area of the Asian monsoon in the Hexi Corridor of NW China. Our results show that alluvial and aeolian deposition before 10.4 cal ka BP indicate an arid environment, that lacustrine deposition from 10.4 to 8.8 cal ka BP indicates a transition from an arid to a humid environment, and that lacustrine deposition from 8.8 to 5.5 cal ka BP occurred during the most humid conditions, indicated by proxy records (grain size, carbonate, TOC, and C/N). After 5.5 cal ka BP, a depositional hiatus implicates an arid environment in the late Holocene. Holocene environmental changes on millennial timescales in Huahai Lake imply that climate was arid to humid in the early Holocene, most humid in the mid-Holocene and arid in the late Holocene. These moisture changes were influenced by the Asian monsoon, particularly the transportation of water vapor by the Indian monsoon. In addition, these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid-Holocene. The most humid conditions that occurred in the study area during the mid-Holocene may have been caused by strong westerlies and low levels of evaporation. [Copyright &y& Elsevier]

Abstract: Deposits from the Huahai ancient lake in the Hexi Corridor were dated using conventional and AMS 14C. A 2500a “carbon storage effect” was defined at 9.25 m depth according to the 14C age difference between a plant macrofragment and detrital organic matter from the same layer. The chronology of this strata indicated that the mirabilite layer at the depth of 8.05 m–9.15 m had formed during the Younger Dryas (YD) event. The formation of the mirabilite layer indicated that the mean annual temperature in the Hexi Corridor dropped by 11 C° during the YD event compared with today. The lowest cold event occurred early in the YD, which is consistent with what has been revealed by other high-resolution records, such as those of Arctic ice cores and stalagmites in mid-latitude regions. [Copyright &y& Elsevier]