巴颜喀拉山青康公路沿线多年冻土和活动层分布特征及影响因素

Distributive Features and Controlling Factors of Permafrost and the Active Layer Thickness in the Bayan Har Mountains along the Qinghai-Kangding Highway on Northeastern Qinghai-Tibet Plateau

巴颜喀拉山是较典型的高海拔多年冻土区。南、北坡迥异的气候、土壤及地表景观控制和影响其多年冻土空间分布。2008~2012年冻土调查及测温资料表明，该山以高温冻土（〉-1℃）为主。海拔是冻土主要影响因素。年均地温随海拔升高而降低的高程递减率在北坡6℃／km，南坡4℃／km。北坡查拉坪及巴颜喀拉山口一带，活动层厚度约1m，活动层随海拔降低而增厚；南坡活动层厚度受局地因素影响较大，与海拔无明显相关。

Permafrost on the Qinghai-Tibet Plateau （QTP） is elevational, where the permafrost accounts for approximately 75% of the elevational permafrost in the Northrn hemisphere. Located in the transition zone from the Qinghai-Tibet Plateau higher than 4 500 m a. s. 1. to the Loess Plateau at less than 2 000 m a. s. 1., the Bay- an Har Mountains （BHM） have typical alpine permafrost. The intensive uplifts of the BHM have resulted in a great variety in climate, permafrost and landscapes on the north and south slopes. Based on field investigations and ground temperature measurements between 2008-2012, the distributive features and controlling/influenc- ing factors of permafrost in the BHM are revealed in detail in this paper. Most permafrost in the BHM is warm （〉-1 ~C）, except that at some mountain tops such as Chalaping and the Bayan Har Mountain Pass. The ground temperature in the BHM is principally controlled by elevations. The lowest MAGT of-l.8℃ and the thickest permafrost of 74 m are found at Chalaping higher than 4 700 m a. s. 1. The lapse rate of MAGT with rising elevation is 6℃/kin on the north slopes and 4℃/kin on the south slopes, respectively. The MAGTs are -0.2℃ in Borehole YNG-1 at the north-slope toes, and ＋0.3℃ in Borehole QSH-1 at the south-slope toes. Permafrost thins rapidly downwards at both slope toes. The MAGTs are lower than -0.5 ℃ at elevations above 4 570 m a. s. 1. on the south slopes and above 4 527 m a. s. 1. on the north slopes. The MAGTs are lower.than -1 ℃ at eleva- tions above 4 670 m a. s. 1. on the south slopes and above 4 615 m a. s. 1. on the north slopes. The zone boundaries of-0.5℃ in mean annual ground temperatures largely coincide with the lower limits of sporadic （discontinuous） permafrost, and zone boundaries of-1 ℃ correspond to the lower limits of continuous permafrost. The active layer thickness, which usually affected by the lithology （soil types） and moisture conditions, is about 1 m at the Bayan Har Mountain Pass and Chalaping on the north slopes. It increases with declining elevation. However, on the south slopes, it is greatly influenced by some local factors, such as vegetative coverage and soil mois- ture contents. For example, the active layer is more than 4 m deep in Borehole CLQ-1 at 4 642 m a. s. 1., where the surface vegetation coverage is low, and soils and alpine meadows are broken by rodent and insect activities.