Permafrost and paleoenvironments on the Northeastern Qinghai-Tibet Plateau, China during the local last permafrost maximum

The Qinghai-Tibet Plateau (QTP) is one of the middle- and low-latitude regions with the most developed and well-preserved periglacial phenomena and remains in the world. On the northeastern QTP, periglacial remains are widespread and vital for investigating the evolution of regional periglacial and permafrost environments. The recently discovered periglacial remains on the northeastern QTP are mostly cryogenic wedges of Late Pleniglacial age (30–10 ka), deep and large cryogenic wedges mostly formed during 30–19 ka ago. Shallow cryogenic wedges have formed between 16 and 12.5 ka. A second wave of cryogenic wedge pseudomorphs seems to have followed, which was ending by about 7 ka. Based on the types of cryogenic wedges and in combination with stratigraphic data for dating, as well as the past Quaternary geological and periglacial landform data, we infer that the mean annual air temperature (MAAT) in this region during the local LPM (30–19 ka) was 7–9°C lower than that at present, and the lower limit of permafrost was lowered to about 2,200–2,500 m a. s. l. During the local LPM, permafrost was extensively and intensively developed on the northeastern QTP, and the continuous permafrost zone extended down to the source area of the Yellow River and the vicinity of the Zoîgé Plateau in the east. Next, discontinuous, sporadic and patchy permafrost occur in cascadingly lowering zones.