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This paper presents the environmental history and its responses to palaeoclimatic changes since the start of the Holocene in the eastern portion of the desert belt (sand seas and sandy lands) in northern China by comparing the aeolian sandpalaeosol sequences and their palaeoclimatic proxies. The optically stimulated luminescence (OSL) ages of the aeolian sandpalaeosol sedimentary sequences and a series of palaeoenvironmental proxies show that: (1) The large-scale dune landscape currently in the Kubuqi Sand Sea was formed during the Holocene in general; and the palaeosol was generally developed during the period of 4–2 ka, indicating conditions favorable for vegetation growth, soil development, and organic carbon accumulation due to increased precipitation or effective moisture and weakened aeolian activities; the large-scale expansion of dunes in the recent 2 ka is closely linked to human activities. The variable discharge of the Yellow River with diversions for irrigation may have resulted in a more consistent supply of aeolian particles for dune field expansion. (2) The dune landscape of the Hunshandake Sandy Land was likely formed around 12 ka, and before this, the western part of the Hunshandake Sandy Land would have been covered by a single large lake; it was obviously wetter than today in the sandy land during the period of 9.6–3 ka and the palaeosols were developed at the same time. But the aeolian activities have not been completely dormant in this long-lasting wetter epoch; because the Holocene wetter period was likely time-transgressive across the region. (3) The palaeosol of the Hulunbuir Sandy Land began to develop as early as 14.5 ka, probably continuing until the last 2 ka. The palaeosol development of various dune fields in the eastern portion of the desert belt (sand seas and sandy lands) in northern China is spatially heterogeneous, and even the palaeosol development time in different locations within each sandy land is inconsistent. During the middle Holocene (especially the 7.5–3.5 ka), all the sandy lands were stabilized in general and the intensity of aeolian activities was significantly weakened. The number of palaeoenvironmental records in the eastern portion of the desert belt (sand seas and sandy lands) in northern China has increased rapidly in the past decade, but the amount of published data still does not match the vast extent of the dune fields. It does require much more in-depth palaeoenvironmental studies for a full understanding of the relationship between aeolian activities and climate change in northern China. [ABSTRACT FROM AUTHOR]

Although water is scarce in most deserts of the world, the middle-latitude desert of Hunshandake, China, has abundant water resources, mainly groundwater. In this study, isotopic and hydrochemical compositions were investigated to understand the recharge of groundwater in this desert. The groundwaters are fresh and depleted in δ2H and δ18O, compared with modern precipitation, but have high values of tritium (5-25 TU), indicating that these groundwaters are likely less than 70 years old but not of meteoric origin. Clear differences were observed between the north and south parts of the desert. Groundwater in the northern part is characterized by lower landform elevation, lower ion concentrations, higher tritium contents, higher deuterium excess, and more depleted values of δ2H and δ18O than that in the southern part. This indicates a discrepancy between the topographic hydraulic gradient and the isotopic and hydrochemical gradients of groundwater in the desert. It also implies different water sources between the two areas. Combined analysis was further performed on natural waters from the Dali Basin and surrounding mountains. It indicated that groundwater in the north is mainly sourced from the Daxin'Anling Mountains, by leaking of the Xilamulan River water through a thick faulted aquifer. Groundwater in the south has two sources, the Yinshan Mountains and Daxing'Anlin Mountains. Therefore, modern focused recharge is more significant for groundwater recharge in the desert than the mechanisms of diffuse recharge. A conceptual model of groundwater recharge is proposed: the MTVG (mountain water - tectonic fault hydrology - unconfined vadose zone - groundwater) mechanism. [ABSTRACT FROM AUTHOR]