FLUCTUATING DESERT MARGINS AND HYDROLOGICAL CHANGE DURING AND SINCE THE LATE QUATERNARY GLACIATION OF TIBET AND THE BORDERING MOUNTAINS

The glaciers of western China are some of the most diverse in the world in respect of types of thermal regime, a characteristic of fundamental palaeohydrological importance. Almost 80% of China’s ca. 2 million km2 of permafrost lies in this region. Extent and timing of glaciations and their hydrological responses remain poorly defined, however, current understanding resting upon some poorly-constrained glacial stages, changes in the presence/absence and levels of lake waters, palaeofluvial changes, and dryland stratigraphy.

Deserts change in response to interactions between atmosphere, hydro-biosphere, and lithosphere. In turn, dryland changes stimulate important feedback effects including surface albedo changes and injection into the atmosphere of mineral aerosols affecting both radiative balance and global carbon cycle. The glacial and dryland/desert margin palaeoclimatic records are variously inferential, resting to different degrees upon the relatively well-dated, high-resolution and semi-continuous record on the Loess Plateau. Periodic increases in sand/coarse silt content within the loess indicate enlargement of the drylands as major dust sources; in the LGM margins shifted several hundred km to south and east of the Holocene Optimum line.

Reported high lake levels in OIS-3 have been explained in terms of glacier melting rather than increased rainfall. However, correlation between glaciation and higher lake levels remains rather poor for the past 30ka, high lake levels matching some glacial advances but not others.

Holocene climatic change patterns are increasingly more complex than the broad tripartite subdivision already recognised. Evidence remains sparse or conflicting concerning early Holocene glacial advance, interpretation of desert fluviatile sediment in its own right and in relationship to glacial advance/retreat, and the climatic signal from some lake records with respect to sub-Milankovitch scale climatic variation.