Niu Fujun, Cheng Guodong, Niu Yonghong, Zhang Mingyi, Luo Jing, Lin Zhanju
State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China.
Sci Rep. 2016 Sep 29;6:34184. doi: 10.1038/srep34184.
Permafrost is determined to a large extent by the Earth's surface temperature, therefore it distributes mainly in high altitude and latitude regions. However, stable, warm (about -1 °C) permafrost occurs within a scree slope in northern China that is more than 600 km south of the southernmost limit of latitudinal permafrost on the Eurasian Continent. It is at an elevation of only 900 m above sea level (ASL). The area has a mean annual air temperature (MAAT) of 6 to 8 °C. Thermal processes of the scree slope, investigated through field monitoring and numerical simulation, showed that the permafrost is caused by winter air convection within the porous rock deposits and is stable as air convection does not occur in summer time. The deposit is covered by a 30-cm-thick peaty soil layer dated (carbon C-14) to between 1,000 to 1,600 years ago. The layer also contributes to the permafrost's existence due to the peat's thermal conductivity offset when frozen and thawed. The existence of permafrost under such warm climatic conditions confirms the effectiveness of using crushed rock layer as basement or slope cover to protect the warm permafrost subgrade of the recently-constructed Qinghai-Tibet Railway (QTR), even under the predicted climate warming conditions.
多年冻土在很大程度上由地球表面温度决定，因此主要分布在高海拔和高纬度地区。然而，在中国北方的一个碎石坡内存在稳定的暖多年冻土（约-1°C），该地区位于欧亚大陆纬度多年冻土最南端界限以南600多公里处，海拔仅900米。该地区年平均气温为6至8°C。通过现场监测和数值模拟对碎石坡的热过程进行研究，结果表明，多年冻土是由多孔岩石沉积物内部的冬季空气对流形成的，由于夏季不发生空气对流，所以多年冻土较为稳定。该沉积物上覆盖着一层厚30厘米的泥炭土层，经碳-14测定，其年代在1000至1600年前。由于泥炭在冻融时的热导率补偿作用，该土层也有助于多年冻土的存在。在如此温暖的气候条件下多年冻土的存在，证实了使用碎石层作为基底或坡面覆盖层来保护新建青藏铁路暖多年冻土路基的有效性，即使在预测的气候变暖条件下也是如此。
