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This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM) permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23–19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N. • Precise location of southern limit of continuous permafrost during the Last Permafrost Maximum (c.19-23 ka) in north China. • Narrow zone of discontinuous/sporadic permafrost during the Last Permafrost Maximum (c.19-23 ka) in north China. • Permafrost extent in N China at LPM was specific by its aridity, continentality and proximity to the Siberian High Pressure. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews our current understanding of Quaternary climate and landscape changes in the desert areas of northern China, a key portion of the middle-latitude drylands on Earth. Combining earlier studies with our recent research and experience, we offer a comprehensive picture of the state of Chinese deserts during the Quaternary and, in the interest of enhancing future research, identify knowledge gaps and areas of uncertainty. Lacustrine deposits found over an area ranging from China’s western Taklamakan Desert to the eastern Hunshandake Sandy Lands suggest that extensive lakes occurred in China’s deserts during the Pleistocene. Analysis of digital elevation models from SRTM (Shuttle Radar Topography Mission) data supports this interpretation and shows the significant extent of these former lakes. New estimates of mean annual evaporation of ca. 1000 mm from lake surfaces and ca. 100 mm from land surfaces, confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone, especially during intervals when the mean annual rainfall is more than 100 mm. Rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of China are very sensitive ephemeral systems, and not long-lasting as previously thought. Available chronologies suggest that there were large lakes in the western Taklamakan Desert and the Chadamu Basin during MIS (Marine Isotope Stage) 3, at ∼30 ka, probably related to a period of strong influence of northern hemispheric westerly winds. Channels and elevation models revealed by SRTM data and remains of lacustrine sediments also indicate that there was a large lake in the Hunshandake Sandy Lands in the eastern portion of the desert belt during the Quaternary. There is significant evidence that during the middle Holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern China. Lacustrine records from the Badain Jaran Desert in western Inner Mongolia suggest that it was generally dry before 10 cal ka, becoming wetter from 10 to 4 cal ka, and dry again afterwards. Study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt, suggests that there was a period of wet and warm climate in this region during the mid-Holocene Optimum, at a minimum between 6 ka and 4 ka, but possibly lasting longer. Recent observations dealing with the generation and transport of dust from Central Asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed. These results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in Chinese deserts are somehow similar to that having occurred in the Sahara Desert of North Africa. Deserts in northern China were also important focal regions for Neolithic cultures during intervals when environmental conditions supported a denser vegetative cover. There is evidence that some areas of woody vegetation to the west of Badain Jaran Desert were deforested by humans by ca. 4000 yr B P, although it is still debatable whether humans have had a significant impact in other areas at that time. Opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long-term, field-based, investigations. [Copyright &y& Elsevier]