EVIDENCE FOR A CYCLIC VARIATION OF PERMAFROST TEMPERATURES IN NORTHERN ALASKA

Observations of permafrost temperatures in shallow drill holes in northern Alaska near the Beaufort Sea coast show that these temperatures have cycled during the decade from 1983 to 1993. The two sites nearest the coast indicate a period of about 10 years and an amplitude at the permafrost surface of about 2 degrees C. The two sites farthest from the coast have similar periods but reduced amplitudes of about 0.6 degrees C. Changes in air temperatures, snowfall, length of sea ice season, solar effects, and other factors could, in principle, produce the observed temperature changes. Barrow air temperatures have a periodicity of 10.1 years but currently lead the sunspot cycle. Snowfall also shows evidence for a periodicity near 10 years. Near Prudhoe Bay, the length of the sea ice season increased about one week from 1979 to 1986 which could have caused a decrease in coastal air temperatures. The sunspot cycle (10-11 year period) leads temperatures at the 30m depth by two to three years which is about the expected lead. During the descending part of the last solar cycle, satellite measurements of the solar total irradiance showed a decrease of about 3W m(-2), which is about four times the calculated mean energy flux at the permafrost table (0.6 to 0.7W m(-2)) required to produce the observed temperature changes.