Permafrost monitoring system in Alaska; structure and results

Permafrost within Alaska varies from cold continues permafrost (-6 to -10 C) on the North Slope to discontinuous and sporadic permafrost in Fairbanks area and further south to Glennallen and Anchorage with temperatures at the permafrost surface of 0 to -2 C. The active layer thicknesses and permafrost temperatures here exhibit significant interannual and decade time scale variations. Moreover, the temperature measurements made here over the last two decades show that permafrost has warmed at all sites along a north-south transect that spans the continuous and most of the discontinuous permafrost zones of Alaska from Prudhoe Bay to Glennallen. Ground temperature measurements and modeling indicate that in the continuous permafrost zone, mean annual permafrost surface temperatures vary interannually within the range of more than 5 C. In the discontinuous permafrost, the observed warming is part of a warming trend that began in the late 1960s. Total magnitude of the warming at the permafrost surface since then is about 2 C. The last "wave" of the recent warming according to observed data began on the Arctic Plain, in the Foothills and at Gulkana in the mid 1980s (typically 1986 or 1987) and in areas of discontinuous permafrost about 1990 (typically 1989 to 1991). The magnitude of the observed warming at the permafrost surface is about 3 to 4 C at West Dock and Deadhorse, Prudhoe Bay region, about 2 C over the rest of the Arctic Coastal Plain and south into the Brooks Range and typically 0.5 to 1.5 C in discontinuous permafrost. Maximum active layer thicknesses were recorded in 1989-1990 and in late 1990s. At some sites in discontinuous permafrost south of the Yukon River, permafrost is now thawing from both the top and bottom. Thawing of ice-rich permafrost is presently creating thermokarst terrain, which has a significant effect on sub-Arctic ecosystems and infrastructure.