Climate controls and high‐altitude permafrost, qinghai‐xizang (tibet) Plateau, China

The high altitude-induced permafrost of the Tibet Plateau reflects a geothermal regime characterized by a strong diurnal pattern, high solar radiation inputs at the surface, and a high geothermal gradient. As a result, the permafrost is relatively [warm] and sensitive to thermal disturbance. Typical permafrost-related processes, such as ice segregation and thermal contraction cracking, are not widespread, and patterned ground phenomena (circles and nets) are restricted to sites of locally high moisture and variable grain size. Ice-rich sediments on north-facing slopes occur mainly as silty colluviums derived from local argillaceous bedrock. Mean annual ground temperatures are usually warmer than −3.5°C. Temperatures at 20 m depth have increased by an average of 0.2 to 0.3°C during the past 15 years. If one assumes continued warming, permafrost is likely to become relict within the next 200 years, and an increase in degradation (i.e. thermokarst processes) is to be expected. Le pergelisol de haute altitude du plateau du Tibet reflete un regime geothermique caracterise par une variation diurne importante, des effets d'une grande radiation solaire a la surface et un gradient geothermique eleve. En consequence, le pergelisol est relativement [chaud] et sensible aux perturbations thermiques. Les processus lie s a la presence d'un pergelisol tels que la glace de segregation et les fissures de contraction thermique, ne sont pas frequents et les sols structuraux periglaciaires (cercles et reseaux) sont limiles aux sites ou l'humidite est elevee et la granulometrie variee. Des sediments riches en glace ont ete trouves sur les pentes exposees au Nord lorsque des colluvions silteuses y existent. Les temperatures moyennes annuelles du sol sont generalement plus chaudes que −3.5°C. Les temperatures a 20 m de profondeur ont augmente en moyenne de 0.2 a 0.3°C pendant les 15 dernieres annees. Si le rechauffement se poursuit, le pergelisol deviendra probablement relict dans les 200 prochaines annees et une augmentation des processus de degradation thermokarstique doit ětre attendue.