Evolution of permafrost on the Qinghai-Xizang (Tibet) Plateau since the end of the late Pleistocene

The present distribution of permafrost on the Qinghai-Xizang (Tibet) Plateau (QTP) is largely a relict of the permafrost formed during the late Pleistocene. It has been degrading and shrinking in areal extent under the fluctuating climates, with a general trend of warming, during the Holocene. The major criteria for the occurrence of relict permafrost include the remnants of ancient buried permafrost, relict permafrost tables, thawed sandwiches (taliks), thick-layered ground ice, and periglacial phenomena such as pingo scars, cryoturbations, primary sand and clayey silt wedges, ice wedge casts, aeolian sand dunes and loesses, thick layers of peat, and humic soils. On the basis of 14 C dating of soils, comprehensive analyses, and comparisons of the spatiotemporal distribution of relict and modern permafrost and periglacial phenomena, the evolution of permafrost and periglacial environments since the late Pleistocene was divided into seven stages: (1) the cold period at the end of the late Pleistocene (35,000 to 10,800 years B. P.); (2) the period of significant climatic change during the early Holocene (10,800 to similar to 8500-7000 years B. P.), (3) the Megathermal period in the middle Holocene (similar to 8500- 7000 to similar to 4000-3000 years B. P.), (4) the cold period in the late Holocene (similar to 4000-3000 to 1000 years B. P.), (5) the warm period in the later Holocene (1000 to 500 years B. P.), (6) the Little Ice Age (500 to 100 years B. P.), and (7) the recent warming period (100 years B. P. to present). The conditions for permafrost development, distribution, and the paleoclimates and paleoenvironments are discussed for each stage.