Arctic permafrost thermal and active layer variability across an environmental gradient from continuous tosporadic permafrost

Permafrost thermal state and active layer thicknesses have been compared from five different Arctic field sites as part of the EU 7th framework project PAGE21. Data has been compiled for the years 2012- 2014 in the following locations: Samoylov and Kytalyk, both in Siberia, Russia, Zackenberg in northeast Greenland, Adventdalen in Svalbard, and Abisko in northern Sweden. These sites were chosen to exemplify the gradient between sporadic and continuous permafrost. The investigated ground thermal data all come from lowland sediment areas, primarily from ice-wedge polygonal landforms, except in the case of Abisko, where the permafrost only exits in palsas. The two Siberian sites have the coldest permafrost, earliest active layer freeze-back periods, and significant annual thermal variation in the upper permafrost. These observations can be explained by the large annual air temperature amplitude in the region, high ground ice content, and limited snow cover. Permafrost temperatures in northeast Greenland are somewhat warmer than in Siberia, but are cooler than those of Svalbard. Seasonal air temperature variation is smaller in northeast Greenland than northern Russia, and this is reflected in the smaller variation in seasonal permafrost temperatures in the prior location. Svalbard permafrost has similar seasonal variability compared to northeast Greenland, but is warmer overall, showing the effect of mild winters. The warmest permafrost was measured at Abisko, where active layer thawing also occurs the earliest. Active layer thickness (ALT) measurements from the five sites, collected via mechanical probing of CALM sites, reflect site meteorological variability in addition to differences in active layer material. In the past few years, only small scale changes in ALT have been observed (both thinning and thickening). However, examining the entire data series shows a general increase in ALT. The permafrost temperature and ALT data highlight climate as a main driver of regional permafrost conditions, but also demonstrate the influence of site specific factors which must be considered at the landscape scale.