Temperature and Depth of Permafrost on the Alaskan Arctic Slope

Analysis of recently measured near-equilibrium temperatures from 25 oil-exploration wells on and near National Petroleum Reserve, Alaska (NPRA) provides the first information on permafrost depth and temperature over large parts of the Arctic Coastal Plain, Foothills province, and northern Brooks Range. Repeated measurements taken over a 7-year period permit an estimate of natural (predrilling) temperatures to within ~0.1°C and of the permafrost depths to within a few meters. Most of the wells show conspicuous evidence of climatic warming during the last century. Permafrost thickness in NPRA generally ranges between 200 and 400 m (650 and 1,300 feet) (compared to 600+ m (2,000 feet) at Prudhoe Bay); there are large local variations and no conspicuous regional trends. By contrast the long-term mean temperature of the ground surface (one factor determining permafrost depth) varies systematically from north to south in a pattern modified by the regional topography and distance from the Arctic Ocean. The observed variation in permafrost temperature and depth cannot result primarily from effects of surface bodies of water or from broad regional variations in crustal heat flow; they are consistent, however, with expectable variations in the thermal conductivity of the sediments. It remains to be determined (with conductivity measurements) whether certain sites with anomalously high gradients have anomalously high local heat flow. If they do, they might indicate long-term upwelling motions of interstitial fluids in the underlying basin sediments.