The evolution of dry lands in northern China and in the Republic of Mongolia since the Last Glacial Maximum

Abstract

The dry lands in China and Mongolia include sand seas, gravel deserts, stable sand dunes, desert steppe, steppe and scrub-woodlands environments distributed in a wide range of geomorphological and tectonic settings, from 155 m below sea level to more than 5000 m asl. In China, the sandy deserts and gravel deserts are located in the arid regions mainly west of the Helan Mountains (∼106°E), whereas the stable dune regions are distributed in the semi-arid areas east of the Helan Mountains. In Mongolia, deserts cover more than 40% of the country. They are mainly distributed in the southern and southwestern part of the country, in inter-mountain valleys and basins of the Altai Mountains, and in the Uvs Nuur Basin in northwestern Mongolia. The desert regions enclose mainly gravel desert (=Gobi) and comprise some areas with sand fields and dune fields, especially in western Mongolia. Relict frost wedges and moraines in the Chaidamu and Tarim basins of China indicate that the coldest time of the last glaciation occurred at 30–25 ka in these two areas. The stratigraphy of the dunes in the Badain Jaran Desert, high lake levels in the areas near and within the large deserts in China and in Mongolia suggest a much more humid climate in western China and in Mongolia during marine isotope stage three. However, the period after 24 ka to the end of the Pleistocene was mostly characterised by increased temperature and reduced precipitation in the Chaidamu and Tarim basins. Paleoenvironmental conditions in the eastern part of the Chinese desert belt were marked by an extensive widening of dune formation at ∼21–13 ka, reflecting a weaker intensity of East Asian summer monsoon. During the Holocene, higher lake levels, stratigraphy of dunes and results of palynological, isotopical and sedimentological analyses of lacustrine sediments in the western China and Mongolia suggest a few wetter periods, especially in the earlier part of the Holocene. The Holocene climatic conditions in the eastern part of the Chinese deserts have enabled stabilisation of dunes and formation of soils. The presently active dunes in this region are a result of desertification due to human influences. Recent investigations in the dry lands of China and Mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates.