Discovered in the late 1980s, inactive ice wedges in Yitulihe in the north part of Da Hinggan Mountains, Northeastern China are the southernmost in the Northern Hemisphere, and they are important paleo-environmental indicators. Recently, research was carried out to analyze the hydrogen and oxygen isotopes of an inactive ice wedge from them. The plot of stable isotopes reveals three periods of temperature fluctuations centered approximately at 2.8, 2.3 and 1.9 ka BP. And the resultant temperature was probably lowered by about 2.1, 1.1, and 1.3℃, respectively, in comparison with present temperatures. In conjunction with previous studies, pollen record and radiocarbon dating, the ice wedges probably developed between 3.3 to 1.6 ka BP, and the southern limit of the permafrost （SLP） at that time advanced southwards by around 2°N, i.e., about 200 km.
