Precise temperature measurements have been made in drill holes in discontinuous permafrost in Alaska since 1976. The holes are primarily in undisturbed permafrost on a north-south transect of Alaska along the trans-Alaska pipeline. Most of the discontinuous permafrost south of the Yukon River is very warm, usually warmer than -2_C with some of the marginal permafrost (e.g., at the toes of south-facing slopes) warmer than -0.5_C. Holes in undisturbed permafrost in this region have recently warmed.

The largest warming occurred near Fairbanks at a cold site in the Chena River floodplain where the mean temperature at the permafrost table (-3.5_C) increased by about 1.5_C from 1990 to 1993. Temperatures at this site were nearly stable prior to the warming (1983-1990). Permafrost near Birch Lake has warmed about 0.5_C from 1984 to 1993. Direct evidence of talik formation and thawing at the permafrost table has been found at four sites in undisturbed permafrost. Measurements of the position of the permafrost table at a disturbed site (a field cleared for agricultural purposes) which have been made since 1976 show that the rate of thawing has increased since 1988.Temperature profiles in thawing permafrost change very slowly with time and, at some of these sites, there is an obvious freezing point depression at the base of the permafrost. These effects are interpreted to be a result of the presence of unfrozen water in the permafrost.

Collectively, the above results show that much of the undisturbed discontinuouspermafrost south of the Yukon River has warmed significantly and that some of it is thawing. Considering the magnitude and distribution of the warming indicated by these very sparse data, it is inferred that much of the discontinuous permafrost in Alaska south of the Yukon River and on the south side of the Seward Peninsula must be currently thawing. Additional measurements are needed to confirm this conclusion.

NSF Grant: Scientific personnel; T. Osterkamp.