The Permafrost Boundary Evolution History From The Penultimate Glacial In China

In this paper, the ice-wedge casts found in Erdos plateau were described in detail. As an evidence in reconstructing paleotemperature, periglacial geomorphological phenomena like ice-wedge cast, sand wedge was considered to be an important factor in paleoenvironmental research for a long period. From the TL dating and sediment analysis of the wedges, it is confirmed that the ice-wedge casts which we found in Erdos developed in the period of Penultimate Glacial. According to the characteristics and the distribution of these ice-wedge casts, we reconstructed the permafrost boundary of the Penultimate Glacial in China and the paleotemperatures on the boundary supported by the correlative formulas among geographic factors. This boundary was divided into three parts, the east part, the middle part and the west part, respectively. Chiefly based on latitude, the east part of the boundary in the area which was east to 118°E existed near 40°20'N, and the middle one between 105°E and 118°E moved southward to 36°33'N. Chiefly based on height, the west part was located on 3700-4200m in the area which was west to 105°E. In addition, the mean annual air temperature of the entire boundary during the penultimate glacial can beestimated to be 10～15℃lower than the temperature nowadays.Because of the paleo-periglacial phenomena found by scientists are all concentrate on 3 periods, which are 23-30ka B.P., 15-20ka B.P. and 6-10ka B.P.. Synthesize the former research, we discuss the permafrost distribution during 3 different periglacial periods respectively and reconstruct the permafrost boundary of LGM in detail.Pollen research can provide the paleotemperature conditions in the periods that we can not find periglacial evidence as supports. Based on the paleotemperature models which are built though pollen research, we reconstruct the permafrost boundary during the last inter-glacial and warm period in the Holocene which are both relatively warmer than nowadays. Based on the paleotemperature rebuilds and the permafrost boundary reconstructions, we approximately establish the permafrost boundary evolution history from the Penultimate Glacial in China.