Temperature profiles measured in permafrost in northernmost Alaska usually have anomalous curvature in the upper 100 meters or so. When analyzed by heat-conduction theory, the profiles indicate a variable but widespread secular warming of the permafrost surface, generally in the range of 2 to 4 Celsius degrees during the last few decades to a century. Although details of the climatic change cannot be resolved with existing data, there is little doubt of its general magnitude and timing; alternative explanations are limited by the fact that heat transfer in cold permafrost is exclusively by conduction. Since models of greenhouse warming predict climatic change will be greatest in the Arctic and might already be in progress, it is prudent to attempt to understand the rapidly changing thermal regime in this region.

Temperature measurements through permafrost in the oil field at Prudhoe Bay, Alaska, combined with laboratory measurements of the thermal conductivity of drill cuttings permit an evaluation of in situ thermal properties and an understanding of the general factors that control the geothermal regime. A sharp contrast in temperature gradient at ∼600 m represents a contrast in thermal conductivity caused by the downward change from interstitial ice to interstitial water at the base of permafrost under near steady state conditions. Interpretation of the gradient contrast in terms of a simple model for the conductivity of an aggregate yields the mean ice content (∼39%), and thermal conductivities for the frozen and thawed sections (8.1 and 4.7 mcal/cm s °C, respectively). These results yield a heat flow of ∼1.3 HFU, which is similar to other values on the Alaskan Arctic Coast; the anomalously deep permafrost is a result of the anomalously high conductivity of the siliceous ice‐rich sediments. Curvature in the upper 160 m of the temperature profiles represents a warming of ∼1.8°C of the mean surface temperature and a net accumulation of 5–6 kcal/cm2 by the solid earth surface during the last 100 years or so. Rising sea level and thawing of ice‐rich sea cliffs probably caused the shoreline to retreat tens of kilometers in the last 20,000 years, inundating a portion of the continental shelf that is presently the target of intensive oil exploration. A simple conduction model suggests that this recently inundated region is underlain by near‐melting ice‐rich permafrost to depths of 300–500 m; its presence is important to seismic interpretations in oil exploration and to engineering considerations in oil production. With confirmation of the permafrost configuration by offshore drilling, heat conduction models can yield reliable new information on the chronology of arctic shorelines.

Twenty heat‐flow measurements were made from drifting ice in a 100‐km equidimensional region on the boundary between the Alpha rise and the Canada basin in the central Arctic Ocean. The heat flow in the basin is uniform (1.41±4% μcal/cm2 sec) over a distance of at least 75 km from the boundary. On the flank of the rise, six consecutive measurements confirm a decrease in heat flow to a minimum of 0.77 in a distance of less than 25 km. The anomaly cannot be explained in terms of superficial effects relating to water circulation, sedimentary processes, or topography. Uniformity of heat flow in the basin and the rapid change on the rise preclude credible explanations in terms of source distributions, mantle convection, phase change, or recent tectonic movements. The anomaly can be explained in terms of relatively low‐conductivity rock extending to a depth of 10 or 20 km, either locally under the low heat‐flow zone or generally under the entire rise. In the latter case, a projection would extend 50 or more kilometers under the adjacent basin at depth. In either case, low heat flow would occur only at the periphery of the rise. It is unlikely that conductivity contrasts in the crust and upper mantle would ever cause an appreciable surface heat‐flow anomaly whose width exceeds 100 km. This is less than the spacing of most heat‐flow stations, which therefore yield little information on the subject. Empirical formulas based on water content underestimate sediment conductivity by 10 to 20% on the rise and 5 to 10% in the basin.

A method of measuring the in situ sediment temperatures in deep bore holes drilled to depths of several hundred meters or more beneath the sea floor has been developed. The technique, as presently used aboard the Deep‐Sea Drilling Project (DSDP) drilling vessel Glomar Challenger, involves the emplacement of a temperature sensor, located below a self‐contained digital temperature recorder package, a short distance into the undrilled, thermally undisturbed sediment at the bottom of the drill hole. By measuring the in situ temperature at various depths in a single drill hole it is possible to calculate the thermal gradient for various intervals in the hole. This information, in conjunction with thermal conductivity data measured aboard ship on the sediment cores recovered from the drill hole, permits computation of the heat flow through the oceanic crust. Heat flow values measured in deep drill holes in the Indian and Pacific oceans and in the Bering and Red seas are in generally good agreement with the regional geothermal flux as determined by conventional near‐surface heat flow measurements, suggesting that the thousands of existent shallow heat flow values are representative of the earth's heat flux. Where multiple downhole temperature measurements made at one site permit calculation of interval heat flow values, there is no consistent indication of a significant vertical increase or decrease in heat flux, such as might be caused by long‐term changes in bottom water temperature or the upward migration of interstitial fluids. We note, however, that a more detailed set of temperature measurements in a single hole is required to verify this conclusion. Downhole heat flow values made within a specific physiographic region, such as the Red Sea or the Ninety East ridge, appear to be less variable than, but equal to, the heat flow values calculated using thermal gradient measurements made at shallower depths beneath the sea floor. This observation is in accordance with theoretical considerations which indicate that temperature measurements in deep drill holes are less susceptible than conventional heat flow measurements to the disturbing thermal effects of small‐scale surface topography, short‐term variations in bottom water temperatures, and local sedimentary processes (slumping, erosion).

A fundamental goal of geothermal studies in the Arctic region is to determine the rate of heat flow from deep in the earth’s crust. Research during the past 25 years has shown heat flux is closely related to the tectonic evolution of a geological province. When combined with other geological and geophysical data, accurate heat-flow measurements can set constraints on crustal temperatures, age and evolution of the lithosphere, and the distribution of radiogenic heat in the crust. At an even more fundamental level, accurate measurements help determine the total rate of heat loss from the Earth and define the global variation of heat flow and its correlation with other long-wavelength geophysical features. In addition to the fundamental scientific interest, the subsurface thermal regimes of continents and continental margins of the Arctic are of practical concern for natural resource development. Mean annual surface temperatures on land are well below freezing, which results in a permafrost layer hundreds of meters thick in some places; for example Judge and others (1981) reported a permafrost thickness of 726 m on Cameron Island in the Canadian Arctic Archipelago. The ice-bearing permafrost presents many obstacles to the development of resources and the maintenance of facilities in the Arctic, and as a consequence, a considerable effort has been made by the Canadian and United States governments and industry to evaluate the subsurface thermal regime from an engineering perspective. These efforts have provided many drill holes for subsurface temperature and thermal properties data. Many of these holes will provide